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Seq	Timestamp	Type	Name	Duration
0/0	2026/09/03 19:07	flow	patch-triage	1m Args: null Results: { "EnableConfigs": [ "KVM", "NUMA" ], "FocusSymbols": [ "kvm_gmem_create", "kvm_gmem_bind_node", "mempolicy_create", "mpol_set_shared_policy_range", "mpol_set_shared_policy" ], "KMSANReasoning": "The patch introduces support for the `GUEST_MEMFD_FLAG_BIND_NODE` flag in KVM's guest_memfd subsystem along with helper functions `mempolicy_create()` and `mpol_set_shared_policy_range()` in `mm/mempolicy.c`.\n\nKMSAN vs KASAN applicability:\n- KMSAN detects uninitialized memory reads (on stack, heap, or page allocations) and info-leaks to userspace.\n- In this patch, the `KVM_CREATE_GUEST_MEMFD` ioctl reads user arguments via `copy_from_user` and returns a file descriptor integer; no kernel structures, padding, or buffers are copied back to user space.\n- All newly introduced or modified stack and heap variables (e.g., `nodemask_t nodes` initialized via `init_nodemask_of_node()`, `scratch` initialized via `NODEMASK_SCRATCH()`, and `struct sp_node`/`struct mempolicy` allocated and initialized through standard mm helpers) are fully initialized before use.\n- There are no branching conditions on uninitialized memory or altered data buffer length calculations that could expose uninitialized bytes.\n- Any potential issues (such as NUMA policy reference counting, lifecycle issues, or allocation failures) fall under the scope of KASAN, LOCKDEP, and standard kernel debugging facilities.\n\nTherefore, a dedicated KMSAN fuzzing session is not warranted.", "NeedsKMSAN": false, "Reasoning": "The patch introduces NUMA node binding support for KVM guest_memfd via the GUEST_MEMFD_FLAG_BIND_NODE flag in KVM_CREATE_GUEST_MEMFD, and adds the mempolicy helpers mempolicy_create() and mpol_set_shared_policy_range(). These changes modify reachable kernel logic in mm/mempolicy.c and virt/kvm/guest_memfd.c accessible from userspace.", "WorthFuzzing": true }
1/1	2026/09/03 19:07	action	read-patch-diff	0m Args: null Results: { "PatchDiff": "commit ae68955a5923d25e9e0af9569430579e94c40f9f\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate: Thu Sep 3 19:07:15 2026 +0000\n\n syz-cluster: applied patch under review\n\ndiff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h\nindex 03bfc92864b6e..738e276633c1e 100644\n--- a/include/linux/kvm_host.h\n+++ b/include/linux/kvm_host.h\n@@ -739,6 +739,9 @@ static inline u64 kvm_gmem_get_supported_flags(struct kvm kvm)\n \tif (!kvm \|\| kvm_arch_supports_gmem_init_shared(kvm))\n \t\tflags \|= GUEST_MEMFD_FLAG_INIT_SHARED;\n \n+\tif (IS_ENABLED(CONFIG_NUMA))\n+\t\tflags \|= GUEST_MEMFD_FLAG_BIND_NODE;\n+\n \treturn flags;\n }\n #endif\ndiff --git a/include/linux/mempolicy.h b/include/linux/mempolicy.h\nindex 65c732d440d2f..398318175cec7 100644\n--- a/include/linux/mempolicy.h\n+++ b/include/linux/mempolicy.h\n@@ -124,10 +124,15 @@ int vma_dup_policy(struct vm_area_struct src, struct vm_area_struct dst);\n void mpol_shared_policy_init(struct shared_policy sp, struct mempolicy mpol);\n int mpol_set_shared_policy(struct shared_policy sp,\n \t\t\t struct vm_area_struct vma, struct mempolicy mpol);\n+int mpol_set_shared_policy_range(struct shared_policy sp, pgoff_t start,\n+\t\t\t\t pgoff_t end, struct mempolicy mpol);\n void mpol_free_shared_policy(struct shared_policy sp);\n struct mempolicy mpol_shared_policy_lookup(struct shared_policy sp,\n \t\t\t\t\t pgoff_t idx);\n \n+struct mempolicy mempolicy_create(unsigned short mode, unsigned short flags,\n+\t\t\t\t nodemask_t nodes);\n+\n struct mempolicy get_task_policy(struct task_struct p);\n struct mempolicy __get_vma_policy(struct vm_area_struct vma,\n \t\tunsigned long addr, pgoff_t ilx);\ndiff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h\nindex ac2d77d149635..8d3ae7e2ead8e 100644\n--- a/include/uapi/linux/kvm.h\n+++ b/include/uapi/linux/kvm.h\n@@ -1658,11 +1658,14 @@ struct kvm_memory_attributes {\n #define KVM_CREATE_GUEST_MEMFD\t_IOWR(KVMIO, 0xd4, struct kvm_create_guest_memfd)\n #define GUEST_MEMFD_FLAG_MMAP\t\t(1ULL \u003c\u003c 0)\n #define GUEST_MEMFD_FLAG_INIT_SHARED\t(1ULL \u003c\u003c 1)\n+#define GUEST_MEMFD_FLAG_BIND_NODE\t(1ULL \u003c\u003c 2)\n \n struct kvm_create_guest_memfd {\n \t__u64 size;\n \t__u64 flags;\n-\t__u64 reserved[6];\n+\t__u32 node;\n+\t__u32 pad;\n+\t__u64 reserved[5];\n };\n \n #define KVM_PRE_FAULT_MEMORY\t_IOWR(KVMIO, 0xd5, struct kvm_pre_fault_memory)\ndiff --git a/mm/mempolicy.c b/mm/mempolicy.c\nindex 2ad0a5f18280a..ce10ce4374643 100644\n--- a/mm/mempolicy.c\n+++ b/mm/mempolicy.c\n@@ -1085,7 +1085,45 @@ static int mbind_range(struct vma_iterator vmi, struct vm_area_struct vma,\n \treturn vma_replace_policy(vma, new_pol);\n }\n \n-/* Set the process memory policy /\n+/\n+ mempolicy_create - build a validated, cpuset-contextualised mempolicy\n+ * @mode: MPOL_* mode\n+ * @flags: MPOL_F_* flags\n+ * @nodes: target nodemask, or NULL (interpreted per @mode; see mpol_new())\n+ \n+ Creates a new policy and constrains it to the task's cpuset.\n+ \n+ The caller owns the returned reference and frees it with mpol_put().\n+ \n+ Return: the policy (NULL for a default policy), or an ERR_PTR on failure.\n+ /\n+struct mempolicy mempolicy_create(unsigned short mode, unsigned short flags,\n+\t\tnodemask_t nodes)\n+{\n+\tstruct mempolicy pol;\n+\tNODEMASK_SCRATCH(scratch);\n+\tint err;\n+\n+\tif (!scratch)\n+\t\treturn ERR_PTR(-ENOMEM);\n+\n+\tpol = mpol_new(mode, flags, nodes);\n+\tif (IS_ERR(pol))\n+\t\tgoto out;\n+\n+\ttask_lock(current);\n+\terr = mpol_set_nodemask(pol, nodes, scratch);\n+\ttask_unlock(current);\n+\tif (err) {\n+\t\tmpol_put(pol);\n+\t\tpol = ERR_PTR(err);\n+\t}\n+out:\n+\tNODEMASK_SCRATCH_FREE(scratch);\n+\treturn pol;\n+}\n+EXPORT_SYMBOL_FOR_MODULES(mempolicy_create, \"kvm\");\n+\n static long do_set_mempolicy(unsigned short mode, unsigned short flags,\n \t\t\t nodemask_t nodes)\n {\n@@ -3274,24 +3312,47 @@ void mpol_shared_policy_init(struct shared_policy sp, struct mempolicy mpol)\n }\n EXPORT_SYMBOL_FOR_MODULES(mpol_shared_policy_init, \"kvm\");\n \n-int mpol_set_shared_policy(struct shared_policy sp,\n-\t\t\tstruct vm_area_struct vma, struct mempolicy pol)\n+/*\n+ mpol_set_shared_policy_range - install @pol over [@start, @end) of @sp\n+ * @sp: the shared policy tree\n+ * @start: first page offset (inclusive)\n+ * @end: last page offset (exclusive)\n+ * @pol: a fully-built, validated policy, or NULL to clear the range\n+ \n+ Installs @pol over the given range, replacing any overlapping policy.\n+ * @sp takes its own reference, the caller retains its reference on @pol.\n+ \n+ The policy is not reconstructed, so the policy is preserved exactly.\n+ \n+ Unlike mpol_set_shared_policy(), no VMA is required, so a range that\n+ * is never mapped into a VMA can be covered, including the whole file.\n+ \n+ Return: 0 on success, -ENOMEM on allocation failure.\n+ /\n+int mpol_set_shared_policy_range(struct shared_policy sp, pgoff_t start,\n+\t\t\t\t pgoff_t end, struct mempolicy pol)\n {\n-\tconst pgoff_t pgoff = vma_start_pgoff(vma);\n-\tconst pgoff_t pgoff_end = vma_end_pgoff(vma);\n \tstruct sp_node new = NULL;\n \tint err;\n \n \tif (pol) {\n-\t\tnew = sp_alloc(pgoff, pgoff_end, pol);\n+\t\tnew = sp_alloc(start, end, pol);\n \t\tif (!new)\n \t\t\treturn -ENOMEM;\n \t}\n-\terr = shared_policy_replace(sp, pgoff, pgoff_end, new);\n+\terr = shared_policy_replace(sp, start, end, new);\n \tif (err \u0026\u0026 new)\n \t\tsp_free(new);\n \treturn err;\n }\n+EXPORT_SYMBOL_FOR_MODULES(mpol_set_shared_policy_range, \"kvm\");\n+\n+int mpol_set_shared_policy(struct shared_policy sp,\n+\t\t\tstruct vm_area_struct vma, struct mempolicy pol)\n+{\n+\treturn mpol_set_shared_policy_range(sp, vma-\u003evm_pgoff,\n+\t\t\t\t\t vma-\u003evm_pgoff + vma_pages(vma), pol);\n+}\n EXPORT_SYMBOL_FOR_MODULES(mpol_set_shared_policy, \"kvm\");\n \n / Free a backing policy store on inode delete. /\ndiff --git a/tools/testing/selftests/kvm/guest_memfd_test.c b/tools/testing/selftests/kvm/guest_memfd_test.c\nindex 2233d871a38f4..b333cb42fab29 100644\n--- a/tools/testing/selftests/kvm/guest_memfd_test.c\n+++ b/tools/testing/selftests/kvm/guest_memfd_test.c\n@@ -25,6 +25,31 @@\n \n static size_t page_size;\n \n+static int __create_guest_memfd_node(struct kvm_vm vm, u64 size, u64 flags,\n+\t\t\t\t u32 node, u32 pad)\n+{\n+\tstruct kvm_create_guest_memfd guest_memfd = {\n+\t\t.size = size,\n+\t\t.flags = flags,\n+\t\t.node = node,\n+\t\t.pad = pad,\n+\t};\n+\n+\treturn __vm_ioctl(vm, KVM_CREATE_GUEST_MEMFD, \u0026guest_memfd);\n+}\n+\n+static int create_guest_memfd(struct kvm_vm vm, u64 size, u64 flags, u32 node)\n+{\n+\tint fd;\n+\n+\tif (!(flags \u0026 GUEST_MEMFD_FLAG_BIND_NODE))\n+\t\treturn vm_create_guest_memfd(vm, size, flags);\n+\n+\tfd = __create_guest_memfd_node(vm, size, flags, node, 0);\n+\tTEST_ASSERT(fd \u003e= 0, KVM_IOCTL_ERROR(KVM_CREATE_GUEST_MEMFD, fd));\n+\treturn fd;\n+}\n+\n static void test_file_read_write(int fd, size_t total_size)\n {\n \tchar buf[64];\n@@ -171,6 +196,83 @@ static void test_numa_allocation(int fd, size_t total_size)\n \tkvm_munmap(mem, total_size);\n }\n \n+static bool has_bind_node(struct kvm_vm vm)\n+{\n+\treturn vm_check_cap(vm, KVM_CAP_GUEST_MEMFD_FLAGS) \u0026\n+\t GUEST_MEMFD_FLAG_BIND_NODE;\n+}\n+\n+static void test_bind_node_invalid(struct kvm_vm vm, u64 flags)\n+{\n+\tint fd;\n+\n+\tif (!has_bind_node(vm))\n+\t\treturn;\n+\n+\tfd = __create_guest_memfd_node(vm, page_size,\n+\t\t\t\t flags \| GUEST_MEMFD_FLAG_BIND_NODE, 0, 1);\n+\tTEST_ASSERT(fd \u003c 0 \u0026\u0026 errno == EINVAL,\n+\t\t \"guest_memfd() with non-zero pad should fail with EINVAL\");\n+\n+\tfd = __create_guest_memfd_node(vm, page_size,\n+\t\t\t\t flags \| GUEST_MEMFD_FLAG_BIND_NODE,\n+\t\t\t\t 1 \u003c\u003c 20, 0);\n+\tTEST_ASSERT(fd \u003c 0 \u0026\u0026 errno == EINVAL,\n+\t\t \"guest_memfd() with out-of-range node should fail with EINVAL\");\n+\n+\tfd = __create_guest_memfd_node(vm, page_size, flags, 1, 0);\n+\tTEST_ASSERT(fd \u003c 0 \u0026\u0026 errno == EINVAL,\n+\t\t \"guest_memfd() with a node but no BIND_NODE flag should fail with EINVAL\");\n+}\n+\n+static void test_bind_node(int fd, size_t total_size, int node)\n+{\n+\tconst unsigned long other_mask = 1UL \u003c\u003c (node ? 0 : 1);\n+\tconst unsigned long maxnode = BITS_PER_TYPE(other_mask);\n+\tbool steer_away = is_multi_numa_node_system();\n+\tvoid pages[4];\n+\tint status[4];\n+\tchar mem;\n+\tint i;\n+\n+\tmem = kvm_mmap(total_size, PROT_READ \| PROT_WRITE, MAP_SHARED, fd);\n+\tfor (i = 0; i \u003c 4; i++)\n+\t\tpages[i] = mem + page_size i;\n+\n+\t/\n+\t Bind on a different node if possible order to check whether faulting\n+\t * happens as desired. Without a second node use the local node and\n+\t * just get coverage of create/mmap/fault paths.\n+\t /\n+\tif (steer_away)\n+\t\tkvm_set_mempolicy(MPOL_BIND, \u0026other_mask, maxnode);\n+\n+\t/ Deliberately no mbind() on this mapping. /\n+\tmemset(mem, 0xaa, total_size);\n+\n+\tkvm_move_pages(0, 4, pages, NULL, status, 0);\n+\tfor (i = 0; i \u003c 4; i++)\n+\t\tTEST_ASSERT(status[i] == node,\n+\t\t\t \"Expected page %d on node %d, got it on node %d\",\n+\t\t\t i, node, status[i]);\n+\n+\t/ Dropped memory should fault back onto the same node /\n+\tkvm_fallocate(fd, FALLOC_FL_PUNCH_HOLE \| FALLOC_FL_KEEP_SIZE, 0,\n+\t\t total_size);\n+\tmemset(mem, 0xaa, total_size);\n+\n+\tkvm_move_pages(0, 4, pages, NULL, status, 0);\n+\tfor (i = 0; i \u003c 4; i++)\n+\t\tTEST_ASSERT(status[i] == node,\n+\t\t\t \"Expected page %d back on node %d, got it on node %d\",\n+\t\t\t i, node, status[i]);\n+\n+\tif (steer_away)\n+\t\tkvm_set_mempolicy(MPOL_DEFAULT, NULL, 0);\n+\n+\tkvm_munmap(mem, total_size);\n+}\n+\n static void test_collapse(int fd, u64 flags)\n {\n \tconst size_t pmd_size = get_trans_hugepagesz();\n@@ -404,6 +506,10 @@ static void test_guest_memfd_flags(struct kvm_vm vm)\n \tint fd;\n \n \tfor (flag = BIT(0); flag; flag \u003c\u003c= 1) {\n+\t\t/* BIND_NODE depends on a valid node field, test separately /\n+\t\tif (flag == GUEST_MEMFD_FLAG_BIND_NODE)\n+\t\t\tcontinue;\n+\n \t\tfd = __vm_create_guest_memfd(vm, page_size, flag);\n \t\tif (flag \u0026 valid_flags) {\n \t\t\tTEST_ASSERT(fd \u003e= 0,\n@@ -418,30 +524,40 @@ static void test_guest_memfd_flags(struct kvm_vm vm)\n \t}\n }\n \n-#define ____gmem_test(__test, __vm, __flags, __gmem_size, args...)\t\\\n-do {\t\t\t\t\t\t\t\t\t\\\n-\tint fd = vm_create_guest_memfd(__vm, __gmem_size, __flags);\t\\\n-\t\t\t\t\t\t\t\t\t\\\n-\ttest_##__test(args);\t\t\t\t\t\t\\\n-\tclose(fd);\t\t\t\t\t\t\t\\\n+#define ____gmem_test(__test, __vm, __flags, __gmem_size, __node, args...) \\\n+do {\t\t\t\t\t\t\t\t\t \\\n+\tint fd = create_guest_memfd(__vm, __gmem_size, __flags, __node); \\\n+\t\t\t\t\t\t\t\t\t \\\n+\ttest_##__test(args);\t\t\t\t\t\t \\\n+\tclose(fd);\t\t\t\t\t\t\t \\\n } while (0)\n \n #define __gmem_test(__test, __vm, __flags, __gmem_size)\t\t\t\\\n-\t____gmem_test(__test, __vm, __flags, __gmem_size, fd, __gmem_size)\n+\t____gmem_test(__test, __vm, __flags, __gmem_size, 0, fd, __gmem_size)\n \n #define gmem_test(__test, __vm, __flags)\t\t\t\t\\\n \t__gmem_test(__test, __vm, __flags, page_size * 4)\n \n #define __gmem_test_vm(__test, __vm, __flags, __gmem_size)\t\t\\\n-\t____gmem_test(__test, __vm, __flags, __gmem_size, __vm, fd, __gmem_size)\n+\t____gmem_test(__test, __vm, __flags, __gmem_size, 0,\t\t\\\n+\t\t __vm, fd, __gmem_size)\n \n #define gmem_test_vm(__test, __vm, __flags)\t\t\t\t\\\n \t__gmem_test_vm(__test, __vm, __flags, page_size * 4)\n \n+#define __gmem_test_node(__test, __vm, __flags, __gmem_size, __node)\t\\\n+\t____gmem_test(__test, __vm,\t\t\t\t\t\\\n+\t\t (__flags) \| GUEST_MEMFD_FLAG_BIND_NODE,\t\t\\\n+\t\t __gmem_size, __node, fd, __gmem_size, __node)\n+\n+#define gmem_test_node(__test, __vm, __flags, __node)\t\t\t\\\n+\t__gmem_test_node(__test, __vm, __flags, page_size * 4, __node)\n+\n static void __test_guest_memfd(struct kvm_vm vm, u64 flags)\n {\n \ttest_create_guest_memfd_multiple(vm);\n \ttest_create_guest_memfd_invalid_sizes(vm, flags);\n+\ttest_bind_node_invalid(vm, flags);\n \n \tgmem_test(file_read_write, vm, flags);\n \n@@ -452,6 +568,8 @@ static void __test_guest_memfd(struct kvm_vm vm, u64 flags)\n \t\t\tgmem_test(mmap_supported, vm, flags);\n \t\t\tgmem_test(fault_overflow, vm, flags);\n \t\t\tgmem_test(numa_allocation, vm, flags);\n+\t\t\tif (has_bind_node(vm))\n+\t\t\t\tgmem_test_node(bind_node, vm, flags, 0);\n \t\t\t__gmem_test(collapse, vm, flags, pmd_size);\n \t\t} else {\n \t\t\tgmem_test(fault_private, vm, flags);\ndiff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c\nindex 625e62e1a0318..dc9f071dd969b 100644\n--- a/virt/kvm/guest_memfd.c\n+++ b/virt/kvm/guest_memfd.c\n@@ -423,6 +423,31 @@ static struct mempolicy kvm_gmem_get_policy(struct vm_area_struct vma,\n \t /\n \treturn mpol_shared_policy_lookup(\u0026GMEM_I(inode)-\u003epolicy, pgoff);\n }\n+\n+static int kvm_gmem_bind_node(struct inode inode, int node)\n+{\n+\tstruct mempolicy pol;\n+\tnodemask_t nodes;\n+\tint err;\n+\n+\tif ((unsigned int)node \u003e= MAX_NUMNODES)\n+\t\treturn -EINVAL;\n+\n+\tinit_nodemask_of_node(\u0026nodes, node);\n+\tpol = mempolicy_create(MPOL_BIND, 0, \u0026nodes);\n+\tif (IS_ERR(pol))\n+\t\treturn PTR_ERR(pol);\n+\n+\terr = mpol_set_shared_policy_range(\u0026GMEM_I(inode)-\u003epolicy, 0,\n+\t\t\t\t\t MAX_LFS_FILESIZE \u003e\u003e PAGE_SHIFT, pol);\n+\tmpol_put(pol);\n+\treturn err;\n+}\n+#else\n+static int kvm_gmem_bind_node(struct inode inode, int node)\n+{\n+\treturn -EINVAL;\n+}\n #endif /* CONFIG_NUMA /\n \n static const struct vm_operations_struct kvm_gmem_vm_ops = {\n@@ -520,7 +545,7 @@ bool __weak kvm_arch_supports_gmem_init_shared(struct kvm kvm)\n \treturn true;\n }\n \n-static int __kvm_gmem_create(struct kvm kvm, loff_t size, u64 flags)\n+static int __kvm_gmem_create(struct kvm kvm, loff_t size, u64 flags, int node)\n {\n \tstatic const char name = \"[kvm-gmem]\";\n \tstruct gmem_file f;\n@@ -561,6 +586,12 @@ static int __kvm_gmem_create(struct kvm kvm, loff_t size, u64 flags)\n \n \tGMEM_I(inode)-\u003eflags = flags;\n \n+\tif (flags \u0026 GUEST_MEMFD_FLAG_BIND_NODE) {\n+\t\terr = kvm_gmem_bind_node(inode, node);\n+\t\tif (err)\n+\t\t\tgoto err_inode;\n+\t}\n+\n \tfile = alloc_file_pseudo(inode, kvm_gmem_mnt, name, O_RDWR, \u0026kvm_gmem_fops);\n \tif (IS_ERR(file)) {\n \t\terr = PTR_ERR(file);\n@@ -593,6 +624,7 @@ int kvm_gmem_create(struct kvm kvm, struct kvm_create_guest_memfd args)\n {\n \tloff_t size = args-\u003esize;\n \tu64 flags = args-\u003eflags;\n+\tint node = NUMA_NO_NODE;\n \n \tif (flags \u0026 ~kvm_gmem_get_supported_flags(kvm))\n \t\treturn -EINVAL;\n@@ -600,7 +632,15 @@ int kvm_gmem_create(struct kvm kvm, struct kvm_create_guest_memfd args)\n \tif (size \u003c= 0 \|\| !PAGE_ALIGNED(size))\n \t\treturn -EINVAL;\n \n-\treturn __kvm_gmem_create(kvm, size, flags);\n+\tif (flags \u0026 GUEST_MEMFD_FLAG_BIND_NODE) {\n+\t\tif (args-\u003epad \|\| args-\u003enode \u003e= MAX_NUMNODES)\n+\t\t\treturn -EINVAL;\n+\t\tnode = args-\u003enode;\n+\t} else if (args-\u003enode \|\| args-\u003epad) {\n+\t\treturn -EINVAL;\n+\t}\n+\n+\treturn __kvm_gmem_create(kvm, size, flags, node);\n }\n \n int kvm_gmem_bind(struct kvm kvm, struct kvm_memory_slot *slot,\n" }
2/1	2026/09/03 19:07	agent	patch-evaluator	0m Model: core Args: null Results: { "EnableConfigs": [ "KVM", "NUMA" ], "FocusSymbols": [ "kvm_gmem_create", "kvm_gmem_bind_node", "mempolicy_create", "mpol_set_shared_policy_range", "mpol_set_shared_policy" ], "Reasoning": "The patch introduces NUMA node binding support for KVM guest_memfd via the GUEST_MEMFD_FLAG_BIND_NODE flag in KVM_CREATE_GUEST_MEMFD, and adds the mempolicy helpers mempolicy_create() and mpol_set_shared_policy_range(). These changes modify reachable kernel logic in mm/mempolicy.c and virt/kvm/guest_memfd.c accessible from userspace.", "WorthFuzzing": true } Instruction: You are an expert Linux kernel maintainer and security engineer. Your job is to review a provided patch series and evaluate whether it warrants fuzzing with syzkaller. IMPORTANT: The changes have ALREADY been applied and committed as the HEAD commit in your workspace. Do NOT rely on internal assumptions. You must actively use your code access tools to inspect the actual source code, callers, and surrounding context. ================================================================================ 1. CORE TRIAGE PHILOSOPHY ================================================================================ The goal of patch fuzzing is to discover crashes, regressions, exposed latent bugs, and newly triggered assertions introduced by the patch series. - REACHABILITY IS THE PRIMARY GATE: Fuzzing can only discover bugs in code that can actually execute in standard virtualized environments (GCE or QEMU, utilizing software-emulated devices like USB gadgets, netdev, tun/tap). If the modified code is structurally unreachable (see Section 2), it MUST NOT be fuzzed, regardless of whether it adds assertions or complex logic. - DO NOT BLINDLY TRUST "NO FUNCTIONAL CHANGE" (NFCI) OR "REFACTORING" CLAIMS: Patch authors routinely label changes as "cleanups", "refactorings", or state "No functional change intended". Do NOT take these claims at face value. Code refactorings that rearrange logic, introduce helper functions, or alter state management in core subsystems frequently introduce subtle semantic shifts or uncover latent kernel bugs. If reachable executable code is modified or refactored, it MUST be fuzzed. - NEW OR MODIFIED ASSERTIONS IN REACHABLE CODE MUST BE FUZZED: When a patch introduces or modifies runtime checks or assertions (e.g., WARN_ON, VM_WARN_ON, BUG_ON, lockdep_assert) in reachable code paths, it enforces new or stricter invariants. Even if the author believes the invariant always holds, fuzzing is essential to verify whether an unusual sequence of operations can violate it. ================================================================================ 2. WHEN TO RETURN WorthFuzzing=false (NEGATIVE CRITERIA) ================================================================================ Return WorthFuzzing=false ONLY IF all modified code falls strictly into one or more of these categories: - Non-kernel and non-executable changes: * Modifications to Documentation/, comments, or spelling fixes. * User-space directories, self-tests, samples, or scripts (e.g., tools/, samples/, scripts/, usr/) that do not affect the compiled kernel image (vmlinux) or kernel modules. * Purely decorative logging (e.g., message strings in pr_err, printk, dev_info) or tracepoints that do not alter control flow or data structures. * Build system or Kconfig changes that do not alter compiled C logic. - Structurally unreachable hardware: * Vendor-specific PCIe switches, SmartNICs, or GPU drivers (e.g., mlxsw, pds_core, qed, ionic, amdgpu) requiring physical ASIC/PCIe cards not emulated in standard QEMU. - Unreachable execution paths: * Driver teardown callbacks (.remove, .shutdown, pci_unregister_driver) executed only during physical PCI hot-unplug or manual sysfs driver unbinding. * Code paths exclusive to architectures other than the target architecture. ================================================================================ 3. WHEN TO RETURN WorthFuzzing=true (POSITIVE CRITERIA) ================================================================================ Return WorthFuzzing=true whenever the patch touches reachable executable code, including: - Core Subsystems: * Any logic modifications in memory management (mm/), synchronization/locking (kernel/locking/), BPF, scheduler, core networking, VFS, or syscall handling. - Refactorings and Code Cleanups: * Any restructuring of reachable data structures, helper abstractions, or algorithm flows. - Runtime Assertions and Defensive Checks: * Any introduction or alteration of assertions (WARN_ON, VM_WARN_ON, BUG_ON, etc.) in reachable paths. - Reachable Drivers and Protocols: Drivers accessible via virtual buses (virtio, USB gadget, loopback, netlink, binder, sockets, etc.). ================================================================================ 4. EXTRACTING FocusSymbols (PREVENTING DILUTION) ================================================================================ When WorthFuzzing=true, you must extract specific kernel functions into FocusSymbols to guide the fuzzer: - AVOID UBIQUITOUS LIFECYCLE HOT-PATHS: Do NOT list generic, ubiquitous functions called by almost every program in the corpus (including, but not limited to: general memory allocators and deallocators, page fault and trap handlers, or core synchronization primitives; this is not an exhaustive list). Listing ubiquitous functions causes the fuzzer to classify thousands of unrelated tests as "focused", which severely dilutes fuzzing effort away from the actual changes. - TARGET SPECIFIC FEATURE LOGIC AND ENTRYPOINTS: List functions that specifically implement the logic being added or altered, or direct API entrypoints for the subsystem feature under review. - HANDLING STATIC INLINE FUNCTIONS IN HEADERS (.h): Compiler-inlined static functions (such as static inlines in mm/.h or include/linux/.h) lack distinct symbol addresses in vmlinux and cannot be targeted directly by symbol coverage filters. If the changes are primarily in static inline helpers, identify non-static, feature-specific caller functions in .c files that exercise them (avoiding ubiquitous lifecycle wrappers). ================================================================================ 5. IDENTIFYING EnableConfigs ================================================================================ Identify any specific CONFIG_ options required to properly compile and reach the modified code: - Inspect Kconfig files and #ifdef guards; do not make assumptions. - Check "depends on" lines in Kconfig to include any non-standard parent subsystem configs needed. - Strip any 'CONFIG_' prefix (e.g., return "NET_IPV4" instead of "CONFIG_NET_IPV4"). Prefer calling several tools at the same time to save round-trips. Use set-results tool to provide results of the analysis. It must be called exactly once before the final reply. Ignore results of this tool. Prompt: Target architecture: amd64 For your convenience, here is the diff of the changes: commit ae68955a5923d25e9e0af9569430579e94c40f9f Author: syz-cluster <triage@syzkaller.com> Date: Thu Sep 3 19:07:15 2026 +0000 syz-cluster: applied patch under review diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 03bfc92864b6e..738e276633c1e 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -739,6 +739,9 @@ static inline u64 kvm_gmem_get_supported_flags(struct kvm kvm) if (!kvm \|\| kvm_arch_supports_gmem_init_shared(kvm)) flags \|= GUEST_MEMFD_FLAG_INIT_SHARED; + if (IS_ENABLED(CONFIG_NUMA)) + flags \|= GUEST_MEMFD_FLAG_BIND_NODE; + return flags; } #endif diff --git a/include/linux/mempolicy.h b/include/linux/mempolicy.h index 65c732d440d2f..398318175cec7 100644 --- a/include/linux/mempolicy.h +++ b/include/linux/mempolicy.h @@ -124,10 +124,15 @@ int vma_dup_policy(struct vm_area_struct src, struct vm_area_struct dst); void mpol_shared_policy_init(struct shared_policy sp, struct mempolicy mpol); int mpol_set_shared_policy(struct shared_policy sp, struct vm_area_struct vma, struct mempolicy mpol); +int mpol_set_shared_policy_range(struct shared_policy sp, pgoff_t start, + pgoff_t end, struct mempolicy mpol); void mpol_free_shared_policy(struct shared_policy sp); struct mempolicy mpol_shared_policy_lookup(struct shared_policy sp, pgoff_t idx); +struct mempolicy mempolicy_create(unsigned short mode, unsigned short flags, + nodemask_t nodes); + struct mempolicy get_task_policy(struct task_struct p); struct mempolicy __get_vma_policy(struct vm_area_struct vma, unsigned long addr, pgoff_t ilx); diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h index ac2d77d149635..8d3ae7e2ead8e 100644 --- a/include/uapi/linux/kvm.h +++ b/include/uapi/linux/kvm.h @@ -1658,11 +1658,14 @@ struct kvm_memory_attributes { #define KVM_CREATE_GUEST_MEMFD _IOWR(KVMIO, 0xd4, struct kvm_create_guest_memfd) #define GUEST_MEMFD_FLAG_MMAP (1ULL << 0) #define GUEST_MEMFD_FLAG_INIT_SHARED (1ULL << 1) +#define GUEST_MEMFD_FLAG_BIND_NODE (1ULL << 2) struct kvm_create_guest_memfd { __u64 size; __u64 flags; - __u64 reserved[6]; + __u32 node; + __u32 pad; + __u64 reserved[5]; }; #define KVM_PRE_FAULT_MEMORY _IOWR(KVMIO, 0xd5, struct kvm_pre_fault_memory) diff --git a/mm/mempolicy.c b/mm/mempolicy.c index 2ad0a5f18280a..ce10ce4374643 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -1085,7 +1085,45 @@ static int mbind_range(struct vma_iterator vmi, struct vm_area_struct vma, return vma_replace_policy(vma, new_pol); } -/* Set the process memory policy / +/* + * mempolicy_create - build a validated, cpuset-contextualised mempolicy + * @mode: MPOL_* mode + * @flags: MPOL_F_* flags + * @nodes: target nodemask, or NULL (interpreted per @mode; see mpol_new()) + * + * Creates a new policy and constrains it to the task's cpuset. + * + * The caller owns the returned reference and frees it with mpol_put(). + * + * Return: the policy (NULL for a default policy), or an ERR_PTR on failure. + / +struct mempolicy mempolicy_create(unsigned short mode, unsigned short flags, + nodemask_t nodes) +{ + struct mempolicy pol; + NODEMASK_SCRATCH(scratch); + int err; + + if (!scratch) + return ERR_PTR(-ENOMEM); + + pol = mpol_new(mode, flags, nodes); + if (IS_ERR(pol)) + goto out; + + task_lock(current); + err = mpol_set_nodemask(pol, nodes, scratch); + task_unlock(current); + if (err) { + mpol_put(pol); + pol = ERR_PTR(err); + } +out: + NODEMASK_SCRATCH_FREE(scratch); + return pol; +} +EXPORT_SYMBOL_FOR_MODULES(mempolicy_create, "kvm"); + static long do_set_mempolicy(unsigned short mode, unsigned short flags, nodemask_t nodes) { @@ -3274,24 +3312,47 @@ void mpol_shared_policy_init(struct shared_policy sp, struct mempolicy mpol) } EXPORT_SYMBOL_FOR_MODULES(mpol_shared_policy_init, "kvm"); -int mpol_set_shared_policy(struct shared_policy sp, - struct vm_area_struct vma, struct mempolicy pol) +/** + * mpol_set_shared_policy_range - install @pol over [@start, @end) of @sp + * @sp: the shared policy tree + * @start: first page offset (inclusive) + * @end: last page offset (exclusive) + * @pol: a fully-built, validated policy, or NULL to clear the range + * + * Installs @pol over the given range, replacing any overlapping policy. + * @sp takes its own reference, the caller retains its reference on @pol. + * + * The policy is not reconstructed, so the policy is preserved exactly. + * + * Unlike mpol_set_shared_policy(), no VMA is required, so a range that + * is never mapped into a VMA can be covered, including the whole file. + * + * Return: 0 on success, -ENOMEM on allocation failure. + / +int mpol_set_shared_policy_range(struct shared_policy sp, pgoff_t start, + pgoff_t end, struct mempolicy pol) { - const pgoff_t pgoff = vma_start_pgoff(vma); - const pgoff_t pgoff_end = vma_end_pgoff(vma); struct sp_node new = NULL; int err; if (pol) { - new = sp_alloc(pgoff, pgoff_end, pol); + new = sp_alloc(start, end, pol); if (!new) return -ENOMEM; } - err = shared_policy_replace(sp, pgoff, pgoff_end, new); + err = shared_policy_replace(sp, start, end, new); if (err && new) sp_free(new); return err; } +EXPORT_SYMBOL_FOR_MODULES(mpol_set_shared_policy_range, "kvm"); + +int mpol_set_shared_policy(struct shared_policy sp, + struct vm_area_struct vma, struct mempolicy pol) +{ + return mpol_set_shared_policy_range(sp, vma->vm_pgoff, + vma->vm_pgoff + vma_pages(vma), pol); +} EXPORT_SYMBOL_FOR_MODULES(mpol_set_shared_policy, "kvm"); / Free a backing policy store on inode delete. / diff --git a/tools/testing/selftests/kvm/guest_memfd_test.c b/tools/testing/selftests/kvm/guest_memfd_test.c index 2233d871a38f4..b333cb42fab29 100644 --- a/tools/testing/selftests/kvm/guest_memfd_test.c +++ b/tools/testing/selftests/kvm/guest_memfd_test.c @@ -25,6 +25,31 @@ static size_t page_size; +static int __create_guest_memfd_node(struct kvm_vm vm, u64 size, u64 flags, + u32 node, u32 pad) +{ + struct kvm_create_guest_memfd guest_memfd = { + .size = size, + .flags = flags, + .node = node, + .pad = pad, + }; + + return __vm_ioctl(vm, KVM_CREATE_GUEST_MEMFD, &guest_memfd); +} + +static int create_guest_memfd(struct kvm_vm vm, u64 size, u64 flags, u32 node) +{ + int fd; + + if (!(flags & GUEST_MEMFD_FLAG_BIND_NODE)) + return vm_create_guest_memfd(vm, size, flags); + + fd = __create_guest_memfd_node(vm, size, flags, node, 0); + TEST_ASSERT(fd >= 0, KVM_IOCTL_ERROR(KVM_CREATE_GUEST_MEMFD, fd)); + return fd; +} + static void test_file_read_write(int fd, size_t total_size) { char buf[64]; @@ -171,6 +196,83 @@ static void test_numa_allocation(int fd, size_t total_size) kvm_munmap(mem, total_size); } +static bool has_bind_node(struct kvm_vm vm) +{ + return vm_check_cap(vm, KVM_CAP_GUEST_MEMFD_FLAGS) & + GUEST_MEMFD_FLAG_BIND_NODE; +} + +static void test_bind_node_invalid(struct kvm_vm vm, u64 flags) +{ + int fd; + + if (!has_bind_node(vm)) + return; + + fd = __create_guest_memfd_node(vm, page_size, + flags \| GUEST_MEMFD_FLAG_BIND_NODE, 0, 1); + TEST_ASSERT(fd < 0 && errno == EINVAL, + "guest_memfd() with non-zero pad should fail with EINVAL"); + + fd = __create_guest_memfd_node(vm, page_size, + flags \| GUEST_MEMFD_FLAG_BIND_NODE, + 1 << 20, 0); + TEST_ASSERT(fd < 0 && errno == EINVAL, + "guest_memfd() with out-of-range node should fail with EINVAL"); + + fd = __create_guest_memfd_node(vm, page_size, flags, 1, 0); + TEST_ASSERT(fd < 0 && errno == EINVAL, + "guest_memfd() with a node but no BIND_NODE flag should fail with EINVAL"); +} + +static void test_bind_node(int fd, size_t total_size, int node) +{ + const unsigned long other_mask = 1UL << (node ? 0 : 1); + const unsigned long maxnode = BITS_PER_TYPE(other_mask); + bool steer_away = is_multi_numa_node_system(); + void pages[4]; + int status[4]; + char mem; + int i; + + mem = kvm_mmap(total_size, PROT_READ \| PROT_WRITE, MAP_SHARED, fd); + for (i = 0; i < 4; i++) + pages[i] = mem + page_size i; + + /* + * Bind on a different node if possible order to check whether faulting + * happens as desired. Without a second node use the local node and + * just get coverage of create/mmap/fault paths. + / + if (steer_away) + kvm_set_mempolicy(MPOL_BIND, &other_mask, maxnode); + + / Deliberately no mbind() on this mapping. / + memset(mem, 0xaa, total_size); + + kvm_move_pages(0, 4, pages, NULL, status, 0); + for (i = 0; i < 4; i++) + TEST_ASSERT(status[i] == node, + "Expected page %d on node %d, got it on node %d", + i, node, status[i]); + + / Dropped memory should fault back onto the same node / + kvm_fallocate(fd, FALLOC_FL_PUNCH_HOLE \| FALLOC_FL_KEEP_SIZE, 0, + total_size); + memset(mem, 0xaa, total_size); + + kvm_move_pages(0, 4, pages, NULL, status, 0); + for (i = 0; i < 4; i++) + TEST_ASSERT(status[i] == node, + "Expected page %d back on node %d, got it on node %d", + i, node, status[i]); + + if (steer_away) + kvm_set_mempolicy(MPOL_DEFAULT, NULL, 0); + + kvm_munmap(mem, total_size); +} + static void test_collapse(int fd, u64 flags) { const size_t pmd_size = get_trans_hugepagesz(); @@ -404,6 +506,10 @@ static void test_guest_memfd_flags(struct kvm_vm vm) int fd; for (flag = BIT(0); flag; flag <<= 1) { + /* BIND_NODE depends on a valid node field, test separately / + if (flag == GUEST_MEMFD_FLAG_BIND_NODE) + continue; + fd = __vm_create_guest_memfd(vm, page_size, flag); if (flag & valid_flags) { TEST_ASSERT(fd >= 0, @@ -418,30 +524,40 @@ static void test_guest_memfd_flags(struct kvm_vm vm) } } -#define ____gmem_test(__test, __vm, __flags, __gmem_size, args...) \ -do { \ - int fd = vm_create_guest_memfd(__vm, __gmem_size, __flags); \ - \ - test_##__test(args); \ - close(fd); \ +#define ____gmem_test(__test, __vm, __flags, __gmem_size, __node, args...) \ +do { \ + int fd = create_guest_memfd(__vm, __gmem_size, __flags, __node); \ + \ + test_##__test(args); \ + close(fd); \ } while (0) #define __gmem_test(__test, __vm, __flags, __gmem_size) \ - ____gmem_test(__test, __vm, __flags, __gmem_size, fd, __gmem_size) + ____gmem_test(__test, __vm, __flags, __gmem_size, 0, fd, __gmem_size) #define gmem_test(__test, __vm, __flags) \ __gmem_test(__test, __vm, __flags, page_size * 4) #define __gmem_test_vm(__test, __vm, __flags, __gmem_size) \ - ____gmem_test(__test, __vm, __flags, __gmem_size, __vm, fd, __gmem_size) + ____gmem_test(__test, __vm, __flags, __gmem_size, 0, \ + __vm, fd, __gmem_size) #define gmem_test_vm(__test, __vm, __flags) \ __gmem_test_vm(__test, __vm, __flags, page_size * 4) +#define __gmem_test_node(__test, __vm, __flags, __gmem_size, __node) \ + ____gmem_test(__test, __vm, \ + (__flags) \| GUEST_MEMFD_FLAG_BIND_NODE, \ + __gmem_size, __node, fd, __gmem_size, __node) + +#define gmem_test_node(__test, __vm, __flags, __node) \ + __gmem_test_node(__test, __vm, __flags, page_size * 4, __node) + static void __test_guest_memfd(struct kvm_vm vm, u64 flags) { test_create_guest_memfd_multiple(vm); test_create_guest_memfd_invalid_sizes(vm, flags); + test_bind_node_invalid(vm, flags); gmem_test(file_read_write, vm, flags); @@ -452,6 +568,8 @@ static void __test_guest_memfd(struct kvm_vm vm, u64 flags) gmem_test(mmap_supported, vm, flags); gmem_test(fault_overflow, vm, flags); gmem_test(numa_allocation, vm, flags); + if (has_bind_node(vm)) + gmem_test_node(bind_node, vm, flags, 0); __gmem_test(collapse, vm, flags, pmd_size); } else { gmem_test(fault_private, vm, flags); diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c index 625e62e1a0318..dc9f071dd969b 100644 --- a/virt/kvm/guest_memfd.c +++ b/virt/kvm/guest_memfd.c @@ -423,6 +423,31 @@ static struct mempolicy kvm_gmem_get_policy(struct vm_area_struct vma, / return mpol_shared_policy_lookup(&GMEM_I(inode)->policy, pgoff); } + +static int kvm_gmem_bind_node(struct inode inode, int node) +{ + struct mempolicy pol; + nodemask_t nodes; + int err; + + if ((unsigned int)node >= MAX_NUMNODES) + return -EINVAL; + + init_nodemask_of_node(&nodes, node); + pol = mempolicy_create(MPOL_BIND, 0, &nodes); + if (IS_ERR(pol)) + return PTR_ERR(pol); + + err = mpol_set_shared_policy_range(&GMEM_I(inode)->policy, 0, + MAX_LFS_FILESIZE >> PAGE_SHIFT, pol); + mpol_put(pol); + return err; +} +#else +static int kvm_gmem_bind_node(struct inode inode, int node) +{ + return -EINVAL; +} #endif /* CONFIG_NUMA / static const struct vm_operations_struct kvm_gmem_vm_ops = { @@ -520,7 +545,7 @@ bool __weak kvm_arch_supports_gmem_init_shared(struct kvm kvm) return true; } -static int __kvm_gmem_create(struct kvm kvm, loff_t size, u64 flags) +static int __kvm_gmem_create(struct kvm kvm, loff_t size, u64 flags, int node) { static const char name = "[kvm-gmem]"; struct gmem_file f; @@ -561,6 +586,12 @@ static int __kvm_gmem_create(struct kvm kvm, loff_t size, u64 flags) GMEM_I(inode)->flags = flags; + if (flags & GUEST_MEMFD_FLAG_BIND_NODE) { + err = kvm_gmem_bind_node(inode, node); + if (err) + goto err_inode; + } + file = alloc_file_pseudo(inode, kvm_gmem_mnt, name, O_RDWR, &kvm_gmem_fops); if (IS_ERR(file)) { err = PTR_ERR(file); @@ -593,6 +624,7 @@ int kvm_gmem_create(struct kvm kvm, struct kvm_create_guest_memfd args) { loff_t size = args->size; u64 flags = args->flags; + int node = NUMA_NO_NODE; if (flags & ~kvm_gmem_get_supported_flags(kvm)) return -EINVAL; @@ -600,7 +632,15 @@ int kvm_gmem_create(struct kvm kvm, struct kvm_create_guest_memfd args) if (size <= 0 \|\| !PAGE_ALIGNED(size)) return -EINVAL; - return __kvm_gmem_create(kvm, size, flags); + if (flags & GUEST_MEMFD_FLAG_BIND_NODE) { + if (args->pad \|\| args->node >= MAX_NUMNODES) + return -EINVAL; + node = args->node; + } else if (args->node \|\| args->pad) { + return -EINVAL; + } + + return __kvm_gmem_create(kvm, size, flags, node); } int kvm_gmem_bind(struct kvm kvm, struct kvm_memory_slot *slot,
3/2	2026/09/03 19:07	llm	patch-evaluator	0m Model: gemini-3.7-flash Args: null Results: null Tokens: input: 8648 output: 24 thoughts: 653 Thoughts: Analyzing the Guest Memfd Patch Series for Fuzzing Potential Okay, let's break this down. First, it's aimed at amd64, which is good; it's a common target. I need to understand what's being changed and why, to figure out if it's worth fuzzing. Looking at the file modifications, it seems the core is the addition of NUMA node binding for guest memory file descriptors (guest_memfd). * `include/linux/kvm_host.h` is enabling a `GUEST_MEMFD_FLAG_BIND_NODE` if NUMA is enabled when getting supported flags. * `include/linux/mempolicy.h` shows new functions being added related to memory policy, particularly shared policy ranges, with the declaration of `mpol_set_shared_policy_range` and `mempolicy_create`. These are important. * `include/uapi/linux/kvm.h` defines the flag itself and updates the `kvm_create_guest_memfd` structure to include a `node` field, which I would expect. * `mm/mempolicy.c` provides the implementations for those new mempolicy functions, and importantly, it's modifying `mpol_set_shared_policy` to use the new shared range function. That's a key area. * `tools/testing/selftests/kvm/guest_memfd_test.c` adds tests for this node binding. Always good to see testing. * `virt/kvm/guest_memfd.c` implements `kvm_gmem_bind_node`, and updates the creation functions to take the flag into account. So, this is a pretty self-contained set of changes; it's adding the ability to bind guest memfds to specific NUMA nodes. Now, the important part: is this fuzzable? I know `/dev/kvm` ioctls (`KVM_CREATE_GUEST_MEMFD`) are core and reachable from the userspace, and that mempolicy changes are in core memory management. This is definitely reachable in a standard QEMU/syzkaller environment. I'm seeing that NUMA policies and guest memfd are core kernel subsystems. This looks like a solid "WorthFuzzing = true" scenario. Next, I need to verify Kconfig dependencies. I'm expecting `KVM` (or `KVM_INTEL`/`KVM_AMD`, but `KVM` is pretty standard) and `NUMA` to be required. I'll need to check the Kconfig files to see the dependencies, especially where guest_memfd and mempolicy depend on each other. That's the next step.
4/2	2026/09/03 19:07	tool	grepper	0m Args: { "Expression": "KVM_CREATE_GUEST_MEMFD" } Results: { "Output": "Documentation/virt/kvm/api.rst=6357=in flags to have KVM bind the memory region to a given guest_memfd range of\nDocumentation/virt/kvm/api.rst-6358-[guest_memfd_offset, guest_memfd_offset + memory_size]. The target guest_memfd\nDocumentation/virt/kvm/api.rst:6359:must point at a file created via KVM_CREATE_GUEST_MEMFD on the current VM, and\nDocumentation/virt/kvm/api.rst-6360-the target range must not be bound to any other memory region. All standard\n--\nDocumentation/virt/kvm/api.rst=6430=The \"flags\" field is reserved for future extensions and must be '0'.\nDocumentation/virt/kvm/api.rst-6431-\nDocumentation/virt/kvm/api.rst:6432:4.142 KVM_CREATE_GUEST_MEMFD\nDocumentation/virt/kvm/api.rst-6433-----------------------------\n--\nDocumentation/virt/kvm/api.rst-6440-\nDocumentation/virt/kvm/api.rst:6441:KVM_CREATE_GUEST_MEMFD creates an anonymous file and returns a file descriptor\nDocumentation/virt/kvm/api.rst-6442-that refers to it. guest_memfd files are roughly analogous to files created\n--\nDocumentation/virt/kvm/api.rst=6473=The capability KVM_CAP_GUEST_MEMFD_FLAGS enumerates the `flags` that can be\nDocumentation/virt/kvm/api.rst:6474:specified via KVM_CREATE_GUEST_MEMFD. Currently defined flags:\nDocumentation/virt/kvm/api.rst-6475-\n--\nDocumentation/virt/kvm/api.rst-6479- GUEST_MEMFD_FLAG_INIT_SHARED Make all memory in the file shared during\nDocumentation/virt/kvm/api.rst:6480: KVM_CREATE_GUEST_MEMFD (memory files created\nDocumentation/virt/kvm/api.rst-6481- without INIT_SHARED will be marked private).\n--\narch/x86/kvm/Kconfig=83=config KVM_SW_PROTECTED_VM\n--\narch/x86/kvm/Kconfig-90-\t protected VMs are purely a development and testing vehicle for\narch/x86/kvm/Kconfig:91:\t KVM_CREATE_GUEST_MEMFD. Attempting to run a \"real\" VM workload as a\narch/x86/kvm/Kconfig-92-\t software-protected VM will fail miserably.\n--\ninclude/uapi/linux/kvm.h=1649=struct kvm_memory_attributes {\n--\ninclude/uapi/linux/kvm.h-1657-\ninclude/uapi/linux/kvm.h:1658:#define KVM_CREATE_GUEST_MEMFD\t_IOWR(KVMIO, 0xd4, struct kvm_create_guest_memfd)\ninclude/uapi/linux/kvm.h-1659-#define GUEST_MEMFD_FLAG_MMAP\t\t(1ULL \u003c\u003c 0)\n--\ntools/include/uapi/linux/kvm.h=1645=struct kvm_memory_attributes {\n--\ntools/include/uapi/linux/kvm.h-1653-\ntools/include/uapi/linux/kvm.h:1654:#define KVM_CREATE_GUEST_MEMFD\t_IOWR(KVMIO, 0xd4, struct kvm_create_guest_memfd)\ntools/include/uapi/linux/kvm.h-1655-#define GUEST_MEMFD_FLAG_MMAP\t\t(1ULL \u003c\u003c 0)\n--\ntools/testing/selftests/kvm/guest_memfd_test.c=28=static int __create_guest_memfd_node(struct kvm_vm vm, u64 size, u64 flags,\n--\ntools/testing/selftests/kvm/guest_memfd_test.c-37-\ntools/testing/selftests/kvm/guest_memfd_test.c:38:\treturn __vm_ioctl(vm, KVM_CREATE_GUEST_MEMFD, \u0026guest_memfd);\ntools/testing/selftests/kvm/guest_memfd_test.c-39-}\n--\ntools/testing/selftests/kvm/guest_memfd_test.c=41=static int create_guest_memfd(struct kvm_vm vm, u64 size, u64 flags, u32 node)\n--\ntools/testing/selftests/kvm/guest_memfd_test.c-48-\tfd = __create_guest_memfd_node(vm, size, flags, node, 0);\ntools/testing/selftests/kvm/guest_memfd_test.c:49:\tTEST_ASSERT(fd \u003e= 0, KVM_IOCTL_ERROR(KVM_CREATE_GUEST_MEMFD, fd));\ntools/testing/selftests/kvm/guest_memfd_test.c-50-\treturn fd;\n--\ntools/testing/selftests/kvm/include/kvm_util.h=667=static inline int __vm_create_guest_memfd(struct kvm_vm vm, u64 size,\n--\ntools/testing/selftests/kvm/include/kvm_util.h-674-\ntools/testing/selftests/kvm/include/kvm_util.h:675:\treturn __vm_ioctl(vm, KVM_CREATE_GUEST_MEMFD, \u0026guest_memfd);\ntools/testing/selftests/kvm/include/kvm_util.h-676-}\n--\ntools/testing/selftests/kvm/include/kvm_util.h=678=static inline int vm_create_guest_memfd(struct kvm_vm vm, u64 size,\n--\ntools/testing/selftests/kvm/include/kvm_util.h-682-\ntools/testing/selftests/kvm/include/kvm_util.h:683:\tTEST_ASSERT(fd \u003e= 0, KVM_IOCTL_ERROR(KVM_CREATE_GUEST_MEMFD, fd));\ntools/testing/selftests/kvm/include/kvm_util.h-684-\treturn fd;\n--\nvirt/kvm/kvm_main.c=5167=static long kvm_vm_ioctl(struct file *filp,\n--\nvirt/kvm/kvm_main.c-5387-#ifdef CONFIG_KVM_GUEST_MEMFD\nvirt/kvm/kvm_main.c:5388:\tcase KVM_CREATE_GUEST_MEMFD: {\nvirt/kvm/kvm_main.c-5389-\t\tstruct kvm_create_guest_memfd guest_memfd;\n" }
5/2	2026/09/03 19:07	llm	patch-evaluator	0m Model: gemini-3.7-flash Args: null Results: null Tokens: input: 11680 output: 23 thoughts: 22 Thoughts: Here's a summary of my thought process, as requested: KVM Configuration Deep Dive Okay, time to dig into the KVM configuration. My immediate focus is on `CONFIG_KVM_GUEST_MEMFD`. I need to understand its current status and implications. Beyond that, I need to check out any other Kconfigs that are obviously related to it. There's almost certainly a web of dependencies and interactions that I need to map out to get the full picture. My goal is to understand how this specific feature is implemented, how it affects the guest environment, and if there are any subtle knobs that might be worth adjusting. It's time to build a solid mental model of the relevant Kconfig landscape. Let's see what the documentation and source code tell us.
6/2	2026/09/03 19:07	tool	grepper	0m Args: { "Expression": "config KVM_GUEST_MEMFD" } Results: { "Output": "virt/kvm/Kconfig=103=config KVM_GENERIC_MEMORY_ATTRIBUTES\n--\nvirt/kvm/Kconfig-105-\nvirt/kvm/Kconfig:106:config KVM_GUEST_MEMFD\nvirt/kvm/Kconfig-107- select XARRAY_MULTI\n" }
7/2	2026/09/03 19:07	llm	patch-evaluator	0m Model: gemini-3.7-flash Args: null Results: null Tokens: input: 11982 output: 34 thoughts: 20 Thoughts: Here's my attempt at summarizing the thought process, tailored for an expert audience: Analyzing the KVM Configuration Okay, let's dive into the `virt/kvm/Kconfig` file, specifically around line 106. I need to refresh my memory on how this particular option is handled. I suspect we're looking at a Kconfig symbol related to a specific virtualization feature or device. Depending on the context I might be looking for dependencies, default values, or perhaps even comments clarifying the implications of enabling or disabling this option. My goal here is to grasp the configurability of this particular aspect of the KVM setup and its potential impact on performance or functionality. I will pay particular attention to dependencies on other features or hardware, looking for any edge cases.
8/2	2026/09/03 19:07	tool	read-file	0m Args: { "File": "virt/kvm/Kconfig", "FirstLine": 90, "LineCount": 40 } Results: { "Contents": " 90:\t\n 91:\tconfig HAVE_KVM_PM_NOTIFIER\n 92:\t bool\n 93:\t\n 94:\tconfig KVM_GENERIC_HARDWARE_ENABLING\n 95:\t bool\n 96:\t\n 97:\tconfig KVM_ELIDE_TLB_FLUSH_IF_YOUNG\n 98:\t bool\n 99:\t\n 100:\tconfig KVM_MMU_LOCKLESS_AGING\n 101:\t bool\n 102:\t\n 103:\tconfig KVM_GENERIC_MEMORY_ATTRIBUTES\n 104:\t bool\n 105:\t\n 106:\tconfig KVM_GUEST_MEMFD\n 107:\t select XARRAY_MULTI\n 108:\t bool\n 109:\t\n 110:\tconfig HAVE_KVM_ARCH_GMEM_CONVERT\n 111:\t bool\n 112:\t depends on KVM_GUEST_MEMFD\n 113:\t\n 114:\tconfig HAVE_KVM_ARCH_GMEM_RECLAIM\n 115:\t bool\n 116:\t depends on KVM_GUEST_MEMFD\n 117:\t\n 118:\tconfig HAVE_KVM_ARCH_GMEM_INVALIDATE\n 119:\t bool\n 120:\t depends on KVM_GUEST_MEMFD\n 121:\t\n 122:\tconfig HAVE_KVM_ARCH_GMEM_POPULATE\n 123:\t bool\n 124:\t depends on KVM_GUEST_MEMFD\n" }
9/2	2026/09/03 19:07	llm	patch-evaluator	0m Model: gemini-3.7-flash Args: null Results: null Tokens: input: 12640 output: 23 thoughts: 16 Thoughts: Here's my attempt at summarizing the thought process, tailored for an expert audience and written in the first person: Analyzing the Selection of `KVM_GUEST_MEMFD` Okay, so someone's just picked `KVM_GUEST_MEMFD`. Let me quickly break down what that implies in terms of kernel behavior and potential implications. First off, this means they're aiming for a guest memory file descriptor interface, which, technically, isn't new – but its application or the reason for its use warrants deeper scrutiny. My immediate questions are: What's the specific use case prompting this selection? Are we talking about a memory-backed guest? Or is this part of some more intricate memory management strategy? Are they targeting performance gains via direct memory access from userspace, which would be an obvious and generally understood reason? Or is it something more subtle? Then, I'm thinking about the security posture. Using guest memfds introduces potential attack surface considerations – are appropriate safeguards in place to mitigate risks associated with manipulating guest memory from userspace or even from the host side? We need to verify that we're properly considering and hardening all the associated aspects of this architecture. From a performance perspective, I'll need to drill down into the implications on memory overhead. Is the gain in direct memory access worth any introduced overhead from the extra bookkeeping that would be introduced? I need to analyze its impact on memory allocation, deallocation, and the context switching – is the trade-off in latency, which this interface can have, being properly assessed? Ultimately, the 'why' is what I really need to get at. Are there any existing dependencies? Are they relying on this feature as a means of reducing memory copy overhead, supporting shared memory, or maybe even enabling live migration optimizations? Or are they just experimenting? Either way, I'll be interested to see how they leverage this, and if it's done correctly, if this selection is part of a larger, coherent architecture.
10/2	2026/09/03 19:07	tool	grepper	0m Args: { "Expression": "select KVM_GUEST_MEMFD" } Results: { "Output": "arch/arm64/kvm/Kconfig=20=menuconfig KVM\n--\narch/arm64/kvm/Kconfig-38-\tselect GUEST_PERF_EVENTS if PERF_EVENTS\narch/arm64/kvm/Kconfig:39:\tselect KVM_GUEST_MEMFD\narch/arm64/kvm/Kconfig-40-\thelp\n--\narch/x86/kvm/Kconfig=20=config KVM_X86\n--\narch/x86/kvm/Kconfig-49-\tselect KVM_WERROR if WERROR\narch/x86/kvm/Kconfig:50:\tselect KVM_GUEST_MEMFD if X86_64\narch/x86/kvm/Kconfig-51-\n" }
11/2	2026/09/03 19:07	llm	patch-evaluator	0m Model: gemini-3.7-flash Args: null Results: null Tokens: input: 13311 output: 26 thoughts: 95 Thoughts: Here's my thought process, as an expert in my field: Investigating KVM and Memory Management on x86_64 Okay, so I'm looking at how KVM handles memory on x86_64. Specifically, I know that on this architecture, the KVM core (or its specific Intel/AMD/X86 variants) typically leverages `KVM_GUEST_MEMFD`. But I'm curious about the interaction with NUMA. That's always a critical consideration for performance in a virtualized environment, and I need to understand if there are specific behaviors or configurations relating to KVM and Non-Uniform Memory Access. My next step is clear: I need to dig into the kernel source code. I'll check `mm/mempolicy.c` and `virt/kvm/guest_memfd.c` to see how the NUMA configuration (`CONFIG_NUMA`) is being handled, especially with respect to guest memory backed by `memfd`. I anticipate there will be nuances in memory allocation and placement strategies related to NUMA nodes when KVM and `memfd` are involved. This seems like a reasonable starting point to begin a much deeper investigation into the interaction.
12/2	2026/09/03 19:07	tool	grepper	0m Args: { "Expression": "CONFIG_NUMA", "PathPrefix": "mm/" } Results: { "Output": "\nFull output is too long, showing 500 out of 837 lines.\nUse more precise expression if possible.\n\nmm/Makefile=86=obj-$(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP)\t+= hugetlb_vmemmap.o\nmm/Makefile:87:obj-$(CONFIG_NUMA) \t+= mempolicy.o\nmm/Makefile-88-obj-$(CONFIG_SPARSEMEM)\t+= sparse.o\n--\nmm/Makefile=99=obj-$(CONFIG_MIGRATION) += migrate.o\nmm/Makefile:100:obj-$(CONFIG_NUMA) += memory-tiers.o\nmm/Makefile-101-obj-$(CONFIG_DEVICE_MIGRATION) += migrate_device.o\n--\nmm/Makefile=122=obj-$(CONFIG_CMA)\t+= cma.o\nmm/Makefile:123:obj-$(CONFIG_NUMA) += numa.o\nmm/Makefile:124:obj-$(CONFIG_NUMA_MEMBLKS) += numa_memblks.o\nmm/Makefile:125:obj-$(CONFIG_NUMA_EMU) += numa_emulation.o\nmm/Makefile-126-obj-$(CONFIG_GENERIC_ARCH_NUMA) += arch_numa.o\n--\nmm/arch_numa.c=58=EXPORT_SYMBOL(cpumask_of_node);\n--\nmm/arch_numa.c-61-\nmm/arch_numa.c:62:#ifndef CONFIG_NUMA_EMU\nmm/arch_numa.c-63-static void numa_update_cpu(unsigned int cpu, bool remove)\n--\nmm/arch_numa.c=322=void __init arch_numa_init(void)\n--\nmm/arch_numa.c-333-\nmm/arch_numa.c:334:#ifdef CONFIG_NUMA_EMU\nmm/arch_numa.c-335-void __init numa_emu_update_cpu_to_node(int emu_nid_to_phys,\n--\nmm/arch_numa.c=360=void debug_cpumask_set_cpu(unsigned int cpu, int node, bool enable)\n--\nmm/arch_numa.c-382-}\nmm/arch_numa.c:383:#endif / CONFIG_NUMA_EMU /\n--\nmm/cma.c=436=static int __init __cma_declare_contiguous_nid(phys_addr_t basep,\n--\nmm/cma.c-459-\nmm/cma.c:460:\tif (!IS_ENABLED(CONFIG_NUMA))\nmm/cma.c-461-\t\tnid = NUMA_NO_NODE;\n--\nmm/compaction.c=3005=static int sysctl_compaction_handler(const struct ctl_table table, int write,\n--\nmm/compaction.c-3022-\nmm/compaction.c:3023:#if defined(CONFIG_SYSFS) \u0026\u0026 defined(CONFIG_NUMA)\nmm/compaction.c-3024-static ssize_t compact_store(struct device dev,\n--\nmm/compaction.c=3046=void compaction_unregister_node(struct node node)\n--\nmm/compaction.c-3049-}\nmm/compaction.c:3050:#endif / CONFIG_SYSFS \u0026\u0026 CONFIG_NUMA /\nmm/compaction.c-3051-\n--\nmm/damon/core.c=2893=static inline u64 damos_get_some_mem_psi_total(void)\n--\nmm/damon/core.c-2899-\nmm/damon/core.c:2900:#ifdef CONFIG_NUMA\nmm/damon/core.c-2901-static bool invalid_mem_node(int nid)\n--\nmm/damon/core.c=3081=static unsigned long damos_get_node_eligible_mem_bp(struct damon_ctx c,\n--\nmm/damon/core.c-3086-#endif /* CONFIG_DAMON_PADDR /\nmm/damon/core.c:3087:#else / CONFIG_NUMA /\nmm/damon/core.c-3088-static __kernel_ulong_t damos_get_node_mem_bp(\n--\nmm/damon/core.c=3100=static unsigned long damos_get_node_eligible_mem_bp(struct damon_ctx c,\n--\nmm/damon/core.c-3104-}\nmm/damon/core.c:3105:#endif /* CONFIG_NUMA /\nmm/damon/core.c-3106-\n--\nmm/debug.c=171=void dump_mm(const struct mm_struct mm)\n--\nmm/debug.c-191-#endif\nmm/debug.c:192:#ifdef CONFIG_NUMA_BALANCING\nmm/debug.c-193-\t\t\"numa_next_scan %lu numa_scan_offset %lu numa_scan_seq %d\\n\"\n--\nmm/debug.c-220-#endif\nmm/debug.c:221:#ifdef CONFIG_NUMA_BALANCING\nmm/debug.c-222-\t\tmm-\u003enuma_next_scan, mm-\u003enuma_scan_offset, mm-\u003enuma_scan_seq,\n--\nmm/filemap.c=996=EXPORT_SYMBOL_GPL(filemap_add_folio);\nmm/filemap.c-997-\nmm/filemap.c:998:#ifdef CONFIG_NUMA\nmm/filemap.c-999-struct folio filemap_alloc_folio_noprof(gfp_t gfp, unsigned int order,\n--\nmm/hugetlb.c=2238=static nodemask_t policy_mbind_nodemask(gfp_t gfp)\nmm/hugetlb.c-2239-{\nmm/hugetlb.c:2240:#ifdef CONFIG_NUMA\nmm/hugetlb.c-2241-\tstruct mempolicy mpol = get_task_policy(current);\n--\nmm/hugetlb.c=2977=struct folio alloc_hugetlb_folio(struct vm_area_struct vma,\n--\nmm/hugetlb.c-3052-\t\t.nid = nid,\nmm/hugetlb.c:3053:#ifdef CONFIG_NUMA\nmm/hugetlb.c-3054-\t\t.mode = mpol ? mpol-\u003emode : MPOL_DEFAULT,\n--\nmm/hugetlb_cma.c=26=static unsigned int hugetlb_cma_percent_in_node[MAX_NUMNODES] __initdata;\nmm/hugetlb_cma.c-27-\nmm/hugetlb_cma.c:28:#ifdef CONFIG_NUMA\nmm/hugetlb_cma.c-29-static phys_addr_t __init memblock_node_memory_size(int nid)\n--\nmm/hugetlb_sysctl.c=53=static int hugetlb_sysctl_handler(const struct ctl_table table, int write,\n--\nmm/hugetlb_sysctl.c-60-\nmm/hugetlb_sysctl.c:61:#ifdef CONFIG_NUMA\nmm/hugetlb_sysctl.c-62-static int hugetlb_mempolicy_sysctl_handler(const struct ctl_table table, int write,\n--\nmm/hugetlb_sysctl.c-67-}\nmm/hugetlb_sysctl.c:68:#endif / CONFIG_NUMA /\nmm/hugetlb_sysctl.c-69-\n--\nmm/hugetlb_sysctl.c=99=static const struct ctl_table hugetlb_table[] = {\n--\nmm/hugetlb_sysctl.c-106-\t},\nmm/hugetlb_sysctl.c:107:#ifdef CONFIG_NUMA\nmm/hugetlb_sysctl.c-108-\t{\n--\nmm/hugetlb_sysfs.c=86=HSTATE_ATTR(nr_hugepages);\nmm/hugetlb_sysfs.c-87-\nmm/hugetlb_sysfs.c:88:#ifdef CONFIG_NUMA\nmm/hugetlb_sysfs.c-89-\n--\nmm/hugetlb_sysfs.c=280=static struct attribute hstate_attrs[] = {\n--\nmm/hugetlb_sysfs.c-285-\t\u0026surplus_hugepages_attr.attr,\nmm/hugetlb_sysfs.c:286:#ifdef CONFIG_NUMA\nmm/hugetlb_sysfs.c-287-\t\u0026nr_hugepages_mempolicy_attr.attr,\n--\nmm/hugetlb_sysfs.c=306=static int hugetlb_sysfs_add_hstate(struct hstate h, struct kobject parent,\n--\nmm/hugetlb_sysfs.c-338-\nmm/hugetlb_sysfs.c:339:#ifdef CONFIG_NUMA\nmm/hugetlb_sysfs.c-340-static bool hugetlb_sysfs_initialized __ro_after_init;\n--\nmm/hugetlb_sysfs.c=461=static void __init hugetlb_register_all_nodes(void)\n--\nmm/hugetlb_sysfs.c-467-}\nmm/hugetlb_sysfs.c:468:#else\t/* !CONFIG_NUMA /\nmm/hugetlb_sysfs.c-469-\n--\nmm/hugetlb_sysfs.c=482=void __init hugetlb_sysfs_init(void)\n--\nmm/hugetlb_sysfs.c-497-\nmm/hugetlb_sysfs.c:498:#ifdef CONFIG_NUMA\nmm/hugetlb_sysfs.c-499-\thugetlb_sysfs_initialized = true;\n--\nmm/internal.h=76=unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup memcg,\n--\nmm/internal.h-81-\nmm/internal.h:82:#ifdef CONFIG_NUMA\nmm/internal.h-83-extern int sysctl_min_unmapped_ratio;\n--\nmm/internal.h=1128=static inline void mlock_drain_remote(int cpu) { }\n--\nmm/internal.h-1130-\nmm/internal.h:1131:#ifdef CONFIG_NUMA\nmm/internal.h-1132-extern int node_reclaim_mode;\n--\nmm/internal.h=1239=static inline bool vma_is_single_threaded_private(struct vm_area_struct vma)\n--\nmm/internal.h-1246-\nmm/internal.h:1247:#ifdef CONFIG_NUMA_BALANCING\nmm/internal.h-1248-bool folio_can_map_prot_numa(struct folio folio, struct vm_area_struct vma,\n--\nmm/khugepaged.c=1027=static inline gfp_t alloc_hugepage_khugepaged_gfpmask(void)\n--\nmm/khugepaged.c-1031-\nmm/khugepaged.c:1032:#ifdef CONFIG_NUMA\nmm/khugepaged.c-1033-static int collapse_find_target_node(struct collapse_control cc)\n--\nmm/ksm.c-50-\nmm/ksm.c:51:#ifdef CONFIG_NUMA\nmm/ksm.c-52-#define NUMA(x)\t\t(x)\n--\nmm/ksm.c=159=struct ksm_stable_node {\n--\nmm/ksm.c-181-\tint rmap_hlist_len;\nmm/ksm.c:182:#ifdef CONFIG_NUMA\nmm/ksm.c-183-\tint nid;\n--\nmm/ksm.c=202=struct ksm_rmap_item {\n--\nmm/ksm.c-205-\t\tstruct anon_vma anon_vma;\t/ for reverse mapping, when stable /\nmm/ksm.c:206:#ifdef CONFIG_NUMA\nmm/ksm.c-207-\t\tint nid;\t\t/ when node of unstable tree /\n--\nmm/ksm.c=469=static void advisor_stop_scan(void)\n--\nmm/ksm.c-474-\nmm/ksm.c:475:#ifdef CONFIG_NUMA\nmm/ksm.c-476-/ Zeroed when merging across nodes is not allowed /\n--\nmm/ksm.c=857=static struct ksm_stable_node alloc_stable_node_chain(struct ksm_stable_node dup,\n--\nmm/ksm.c-865-\t\tchain-\u003ermap_hlist_len = STABLE_NODE_CHAIN;\nmm/ksm.c:866:#if defined (CONFIG_DEBUG_VM) \u0026\u0026 defined(CONFIG_NUMA)\nmm/ksm.c-867-\t\tchain-\u003enid = NUMA_NO_NODE; / debug /\n--\nmm/ksm.c=3595=KSM_ATTR(run);\nmm/ksm.c-3596-\nmm/ksm.c:3597:#ifdef CONFIG_NUMA\nmm/ksm.c-3598-static ssize_t merge_across_nodes_show(struct kobject kobj,\n--\nmm/ksm.c=3981=static struct attribute ksm_attrs[] = {\n--\nmm/ksm.c-3992-\t\u0026full_scans_attr.attr,\nmm/ksm.c:3993:#ifdef CONFIG_NUMA\nmm/ksm.c-3994-\t\u0026merge_across_nodes_attr.attr,\n--\nmm/memblock.c-105-\nmm/memblock.c:106:#ifndef CONFIG_NUMA\nmm/memblock.c-107-struct pglist_data __refdata contig_page_data;\n--\nmm/memblock.c=610=static int __init_memblock memblock_add_range(struct memblock_type type,\n--\nmm/memblock.c-666-\t\tif (rbase \u003e base) {\nmm/memblock.c:667:#ifdef CONFIG_NUMA\nmm/memblock.c-668-\t\t\tWARN_ON(nid != memblock_get_region_node(rgn));\n--\nmm/memblock.c=1489=int __init_memblock memblock_set_node(phys_addr_t base, phys_addr_t size,\n--\nmm/memblock.c-1491-{\nmm/memblock.c:1492:#ifdef CONFIG_NUMA\nmm/memblock.c-1493-\tint start_rgn, end_rgn;\n--\nmm/memblock.c=2192=static void __init_memblock memblock_dump(struct memblock_type type)\n--\nmm/memblock.c-2207-\t\tflags = rgn-\u003eflags;\nmm/memblock.c:2208:#ifdef CONFIG_NUMA\nmm/memblock.c-2209-\t\tif (numa_valid_node(memblock_get_region_node(rgn)))\n--\nmm/memcontrol-v1.c=1699=static ssize_t mem_cgroup_reset(struct kernfs_open_file of, char buf,\n--\nmm/memcontrol-v1.c-1735-\nmm/memcontrol-v1.c:1736:#ifdef CONFIG_NUMA\nmm/memcontrol-v1.c-1737-\n--\nmm/memcontrol-v1.c=1780=static int memcg_numa_stat_show(struct seq_file m, void v)\n--\nmm/memcontrol-v1.c-1823-}\nmm/memcontrol-v1.c:1824:#endif / CONFIG_NUMA /\nmm/memcontrol-v1.c-1825-\n--\nmm/memcontrol-v1.c=2028=struct cftype mem_cgroup_legacy_files[] = {\n--\nmm/memcontrol-v1.c-2093-\t},\nmm/memcontrol-v1.c:2094:#ifdef CONFIG_NUMA\nmm/memcontrol-v1.c-2095-\t{\n--\nmm/memcontrol.c=378=static const unsigned int memcg_node_stat_items[] = {\n--\nmm/memcontrol.c-409-#endif\nmm/memcontrol.c:410:#ifdef CONFIG_NUMA_BALANCING\nmm/memcontrol.c-411-\tPGPROMOTE_SUCCESS,\n--\nmm/memcontrol.c=598=static const unsigned int memcg_vm_event_stat[] = {\n--\nmm/memcontrol.c-625-#endif\nmm/memcontrol.c:626:#ifdef CONFIG_NUMA_BALANCING\nmm/memcontrol.c-627-\tNUMA_PAGE_MIGRATE,\n--\nmm/memcontrol.c=1591=static const struct memory_stat memory_stats[] = {\n--\nmm/memcontrol.c-1650-\t{ \"pgrefill\",\t\t\tPGREFILL\t\t},\nmm/memcontrol.c:1651:#ifdef CONFIG_NUMA_BALANCING\nmm/memcontrol.c-1652-\t{ \"pgpromote_success\",\t\tPGPROMOTE_SUCCESS\t},\n--\nmm/memcontrol.c=1673=static int memcg_page_state_output_unit(int item)\n--\nmm/memcontrol.c-1702-\tcase PGREFILL:\nmm/memcontrol.c:1703:#ifdef CONFIG_NUMA_BALANCING\nmm/memcontrol.c-1704-\tcase PGPROMOTE_SUCCESS:\n--\nmm/memcontrol.c=5031=int memory_stat_show(struct seq_file m, void v)\n--\nmm/memcontrol.c-5045-\nmm/memcontrol.c:5046:#ifdef CONFIG_NUMA\nmm/memcontrol.c-5047-static inline unsigned long lruvec_page_state_output(struct lruvec lruvec,\n--\nmm/memcontrol.c=5128=static struct cftype memory_files[] = {\n--\nmm/memcontrol.c-5181-\t},\nmm/memcontrol.c:5182:#ifdef CONFIG_NUMA\nmm/memcontrol.c-5183-\t{\n--\nmm/memory-tiers.c=49=static const struct bus_type memory_tier_subsys = {\n--\nmm/memory-tiers.c-53-\nmm/memory-tiers.c:54:#ifdef CONFIG_NUMA_BALANCING\nmm/memory-tiers.c-55-/*\n--\nmm/memory-tiers.c=65=bool folio_use_access_time(struct folio folio)\n--\nmm/memory-tiers.c-71-\nmm/memory-tiers.c:72:#ifdef CONFIG_NUMA_MIGRATION\nmm/memory-tiers.c-73-static int top_tier_adistance;\n--\nmm/memory-tiers.c=131=static struct demotion_nodes node_demotion __read_mostly;\nmm/memory-tiers.c:132:#endif / CONFIG_NUMA_MIGRATION /\nmm/memory-tiers.c-133-\n--\nmm/memory-tiers.c=260=static struct memory_tier __node_get_memory_tier(int node)\n--\nmm/memory-tiers.c-275-\nmm/memory-tiers.c:276:#ifdef CONFIG_NUMA_MIGRATION\nmm/memory-tiers.c-277-bool node_is_toptier(int node)\n--\nmm/memory-tiers.c=521=static inline void establish_demotion_targets(void) {}\nmm/memory-tiers.c:522:#endif /* CONFIG_NUMA_MIGRATION /\nmm/memory-tiers.c-523-\n--\nmm/memory-tiers.c=906=static int __init memory_tier_init(void)\n--\nmm/memory-tiers.c-913-\nmm/memory-tiers.c:914:#ifdef CONFIG_NUMA_MIGRATION\nmm/memory-tiers.c-915-\tnode_demotion = kzalloc_objs(struct demotion_nodes, nr_node_ids);\n--\nmm/memory-tiers.c=939=bool numa_demotion_enabled = false;\nmm/memory-tiers.c-940-\nmm/memory-tiers.c:941:#ifdef CONFIG_NUMA_MIGRATION\nmm/memory-tiers.c-942-#ifdef CONFIG_SYSFS\n--\nmm/memory.c=6117=int numa_migrate_check(struct folio folio, struct vm_fault vmf,\n--\nmm/memory.c-6152-\tcount_vm_numa_event(NUMA_HINT_FAULTS);\nmm/memory.c:6153:#ifdef CONFIG_NUMA_BALANCING\nmm/memory.c-6154-\tcount_memcg_folio_events(folio, NUMA_HINT_FAULTS, 1);\n--\nmm/memory_hotplug.c=186=MODULE_PARM_DESC(auto_movable_ratio,\n--\nmm/memory_hotplug.c-192- /\nmm/memory_hotplug.c:193:#ifdef CONFIG_NUMA\nmm/memory_hotplug.c-194-static bool auto_movable_numa_aware __read_mostly = true;\n--\nmm/memory_hotplug.c=196=MODULE_PARM_DESC(auto_movable_numa_aware,\n--\nmm/memory_hotplug.c-198-\t\t\"\\\"auto-movable\\\" online policy. Default: true\");\nmm/memory_hotplug.c:199:#endif /* CONFIG_NUMA /\nmm/memory_hotplug.c-200-\n--\nmm/memory_hotplug.c=960=static struct zone auto_movable_zone_for_pfn(int nid,\n--\nmm/memory_hotplug.c-1009-\nmm/memory_hotplug.c:1010:#ifdef CONFIG_NUMA\nmm/memory_hotplug.c-1011-\tif (auto_movable_numa_aware \u0026\u0026\n--\nmm/memory_hotplug.c-1013-\t\tgoto kernel_zone;\nmm/memory_hotplug.c:1014:#endif /* CONFIG_NUMA /\nmm/memory_hotplug.c-1015-\n--\nmm/mempolicy.c=793=static int queue_folios_hugetlb(pte_t pte, unsigned long hmask,\n--\nmm/mempolicy.c-842-\nmm/mempolicy.c:843:#ifdef CONFIG_NUMA_BALANCING\nmm/mempolicy.c-844-/*\n--\nmm/mempolicy.c=912=unsigned long change_prot_numa(struct vm_area_struct vma,\n--\nmm/mempolicy.c-929-}\nmm/mempolicy.c:930:#endif /* CONFIG_NUMA_BALANCING /\nmm/mempolicy.c-931-\n--\nmm/mempolicy.c=1207=static long do_get_mempolicy(int policy, nodemask_t nmask,\n--\nmm/mempolicy.c-1307-\nmm/mempolicy.c:1308:#ifdef CONFIG_NUMA_MIGRATION\nmm/mempolicy.c-1309-static bool migrate_folio_add(struct folio folio, struct list_head foliolist,\n--\nmm/mempolicy.c=3375=EXPORT_SYMBOL_FOR_MODULES(mpol_free_shared_policy, \"kvm\");\nmm/mempolicy.c-3376-\nmm/mempolicy.c:3377:#ifdef CONFIG_NUMA_BALANCING\nmm/mempolicy.c-3378-static int __initdata numabalancing_override;\n--\nmm/mempolicy.c=3380=static void __init check_numabalancing_enable(void)\n--\nmm/mempolicy.c-3383-\nmm/mempolicy.c:3384:\tif (IS_ENABLED(CONFIG_NUMA_BALANCING_DEFAULT_ENABLED))\nmm/mempolicy.c-3385-\t\tnumabalancing_default = true;\n--\nmm/mempolicy.c=3419=static inline void __init check_numabalancing_enable(void)\n--\nmm/mempolicy.c-3421-}\nmm/mempolicy.c:3422:#endif / CONFIG_NUMA_BALANCING /\nmm/mempolicy.c-3423-\n--\nmm/migrate.c=2197=struct folio alloc_migration_target(struct folio src, unsigned long private)\n--\nmm/migrate.c-2235-\nmm/migrate.c:2236:#ifdef CONFIG_NUMA_MIGRATION\nmm/migrate.c-2237-static int store_status(int __user status, int start, int value, int nr)\n--\nmm/migrate.c=2633=SYSCALL_DEFINE6(move_pages, pid_t, pid, unsigned long, nr_pages,\n--\nmm/migrate.c-2639-}\nmm/migrate.c:2640:#endif /* CONFIG_NUMA_MIGRATION /\nmm/migrate.c-2641-\nmm/migrate.c:2642:#ifdef CONFIG_NUMA_BALANCING\nmm/migrate.c-2643-/\n--\nmm/migrate.c=2755=int migrate_misplaced_folio(struct folio folio, int node)\n--\nmm/migrate.c-2781-}\nmm/migrate.c:2782:#endif / CONFIG_NUMA_BALANCING /\n--\nmm/mm_init.c-45-\nmm/mm_init.c:46:#ifndef CONFIG_NUMA\nmm/mm_init.c-47-unsigned long max_mapnr;\n--\nmm/mm_init.c=596=void __meminit __init_single_page(struct page page, unsigned long pfn,\n--\nmm/mm_init.c-613-\nmm/mm_init.c:614:#ifdef CONFIG_NUMA\nmm/mm_init.c-615-/\n--\nmm/mm_init.c=678=static inline void fixup_hashdist(void) {}\nmm/mm_init.c:679:#endif / CONFIG_NUMA /\nmm/mm_init.c-680-\n--\nmm/mmzone.c=46=static inline int zref_in_nodemask(struct zoneref zref,\n--\nmm/mmzone.c-48-{\nmm/mmzone.c:49:#ifdef CONFIG_NUMA\nmm/mmzone.c-50-\treturn node_isset(zonelist_node_idx(zref), nodes);\n--\nmm/mmzone.c-52-\treturn 1;\nmm/mmzone.c:53:#endif / CONFIG_NUMA /\nmm/mmzone.c-54-}\n--\nmm/mmzone.c=76=void lruvec_init(struct lruvec lruvec)\n--\nmm/mmzone.c-97-\nmm/mmzone.c:98:#if defined(CONFIG_NUMA_BALANCING) \u0026\u0026 !defined(LAST_CPUPID_NOT_IN_PAGE_FLAGS)\nmm/mmzone.c-99-int folio_xchg_last_cpupid(struct folio folio, int cpupid)\n--\nmm/mprotect.c=686=long change_protection(struct mmu_gather tlb,\n--\nmm/mprotect.c-703-\nmm/mprotect.c:704:#ifdef CONFIG_NUMA_BALANCING\nmm/mprotect.c-705-\t/\n--\nmm/numa_memblks.c=506=int __init numa_fill_memblks(u64 start, u64 end)\n--\nmm/numa_memblks.c-555-\nmm/numa_memblks.c:556:#ifdef CONFIG_NUMA_KEEP_MEMINFO\nmm/numa_memblks.c-557-static int meminfo_to_nid(struct numa_meminfo mi, u64 start)\n--\nmm/numa_memblks.c=591=EXPORT_SYMBOL_GPL(memory_add_physaddr_to_nid);\nmm/numa_memblks.c-592-\nmm/numa_memblks.c:593:#endif /* CONFIG_NUMA_KEEP_MEMINFO /\n--\nmm/oom_kill.c=72=static inline bool is_memcg_oom(struct oom_control oc)\n--\nmm/oom_kill.c-76-\nmm/oom_kill.c:77:#ifdef CONFIG_NUMA\nmm/oom_kill.c-78-/*\n--\nmm/oom_kill.c=122=static bool oom_cpuset_eligible(struct task_struct tsk, struct oom_control oc)\n--\nmm/oom_kill.c-125-}\nmm/oom_kill.c:126:#endif / CONFIG_NUMA /\nmm/oom_kill.c-127-\n--\nmm/oom_kill.c=249=static enum oom_constraint constrained_alloc(struct oom_control oc)\n--\nmm/oom_kill.c-264-\nmm/oom_kill.c:265:\tif (!IS_ENABLED(CONFIG_NUMA))\nmm/oom_kill.c-266-\t\treturn CONSTRAINT_NONE;\n--\nmm/page_alloc.c=167=EXPORT_PER_CPU_SYMBOL(numa_node);\n--\nmm/page_alloc.c-169-\nmm/page_alloc.c:170:#ifdef CONFIG_NUMA\nmm/page_alloc.c-171-DEFINE_STATIC_KEY_TRUE(vm_numa_stat_key);\n--\nmm/page_alloc.c=195=nodemask_t node_states[NR_NODE_STATES] __read_mostly = {\n--\nmm/page_alloc.c-197-\t[N_ONLINE] = { { [0] = 1UL } },\nmm/page_alloc.c:198:#ifndef CONFIG_NUMA\nmm/page_alloc.c-199-\t[N_NORMAL_MEMORY] = { { [0] = 1UL } },\n--\nmm/page_alloc.c=2558=bool decay_pcp_high(struct zone zone, struct per_cpu_pages pcp)\n--\nmm/page_alloc.c-2590-\nmm/page_alloc.c:2591:#ifdef CONFIG_NUMA\nmm/page_alloc.c-2592-/\n--\nmm/page_alloc.c=3179=static inline void zone_statistics(struct zone preferred_zone, struct zone z,\n--\nmm/page_alloc.c-3181-{\nmm/page_alloc.c:3182:#ifdef CONFIG_NUMA\nmm/page_alloc.c-3183-\tenum numa_stat_item local_stat = NUMA_LOCAL;\n--\nmm/page_alloc.c=3665=static inline bool zone_watermark_fast(struct zone z, unsigned int order,\n--\nmm/page_alloc.c-3709-\nmm/page_alloc.c:3710:#ifdef CONFIG_NUMA\nmm/page_alloc.c-3711-int __read_mostly node_reclaim_distance = RECLAIM_DISTANCE;\n--\nmm/page_alloc.c=3713=static bool zone_allows_reclaim(struct zone local_zone, struct zone zone)\n--\nmm/page_alloc.c-3717-}\nmm/page_alloc.c:3718:#else\t/* CONFIG_NUMA /\nmm/page_alloc.c-3719-static bool zone_allows_reclaim(struct zone local_zone, struct zone *zone)\n\n" }
13/2	2026/09/03 19:07	llm	patch-evaluator	0m Model: gemini-3.7-flash Args: null Results: null Tokens: input: 21926 output: 39 thoughts: 40 Thoughts: Here's my summary, as if I were thinking these thoughts: Diving into Guest Memory Management Alright, time to dig into the guts of how KVM handles guest memory, specifically focusing on `virt/kvm/guest_memfd.c`. I need to get a solid grasp of how memory file descriptors are being managed, especially around the crucial functions `kvm_gmem_bind_node` and `kvm_gmem_create`. Understanding these functions is key to seeing how guest memory is allocated, bound to physical memory, and generally interacted with within the KVM framework. I need to trace the flow, paying close attention to any nuances in how memory regions are handled and how `memfd`s are leveraged for guest memory. Let's see how efficiently and securely this is all implemented.
14/2	2026/09/03 19:07	tool	read-file	0m Args: { "File": "virt/kvm/guest_memfd.c", "FirstLine": 415, "LineCount": 50 } Results: { "Contents": " 415:\t\t/\n 416:\t\t Return the memory policy for this index, or NULL if none is set.\n 417:\t\t \n 418:\t\t Returning NULL, e.g. instead of the current task's memory policy, is\n 419:\t\t * important for the .get_policy kernel ABI: it indicates that no\n 420:\t\t * explicit policy has been set via mbind() for this memory. The caller\n 421:\t\t * can then replace NULL with the default memory policy instead of the\n 422:\t\t * current task's memory policy.\n 423:\t\t /\n 424:\t\treturn mpol_shared_policy_lookup(\u0026GMEM_I(inode)-\u003epolicy, pgoff);\n 425:\t}\n 426:\t\n 427:\tstatic int kvm_gmem_bind_node(struct inode inode, int node)\n 428:\t{\n 429:\t\tstruct mempolicy pol;\n 430:\t\tnodemask_t nodes;\n 431:\t\tint err;\n 432:\t\n 433:\t\tif ((unsigned int)node \u003e= MAX_NUMNODES)\n 434:\t\t\treturn -EINVAL;\n 435:\t\n 436:\t\tinit_nodemask_of_node(\u0026nodes, node);\n 437:\t\tpol = mempolicy_create(MPOL_BIND, 0, \u0026nodes);\n 438:\t\tif (IS_ERR(pol))\n 439:\t\t\treturn PTR_ERR(pol);\n 440:\t\n 441:\t\terr = mpol_set_shared_policy_range(\u0026GMEM_I(inode)-\u003epolicy, 0,\n 442:\t\t\t\t\t\t MAX_LFS_FILESIZE \u003e\u003e PAGE_SHIFT, pol);\n 443:\t\tmpol_put(pol);\n 444:\t\treturn err;\n 445:\t}\n 446:\t#else\n 447:\tstatic int kvm_gmem_bind_node(struct inode inode, int node)\n 448:\t{\n 449:\t\treturn -EINVAL;\n 450:\t}\n 451:\t#endif /* CONFIG_NUMA /\n 452:\t\n 453:\tstatic const struct vm_operations_struct kvm_gmem_vm_ops = {\n 454:\t\t.fault\t\t= kvm_gmem_fault_user_mapping,\n 455:\t#ifdef CONFIG_NUMA\n 456:\t\t.get_policy\t= kvm_gmem_get_policy,\n 457:\t\t.set_policy\t= kvm_gmem_set_policy,\n 458:\t#endif\n 459:\t};\n 460:\t\n 461:\tstatic int kvm_gmem_mmap(struct file file, struct vm_area_struct *vma)\n 462:\t{\n 463:\t\tif (!kvm_gmem_supports_mmap(file_inode(file)))\n 464:\t\t\treturn -ENODEV;\n" }
15/2	2026/09/03 19:07	llm	patch-evaluator	0m Model: gemini-3.7-flash Args: null Results: null Tokens: input: 22972 output: 40 thoughts: 29 Thoughts: Here's my analysis of the provided text, rendered in the first person, assuming I'm an expert in the field: Diving into Guest Memory Management in KVM Okay, so we're talking about guest memory management within KVM, specifically the `guest_memfd.c` file. My attention is drawn to the region around lines 540 through 645. That suggests we're looking at a critical section – maybe some allocation or deallocation logic, perhaps related to memory file descriptors for the guest. My initial hypothesis is that we're likely dealing with either: the handling of shared memory regions, or guest memory mapping/unmapping, or perhaps the implementation of a memory-backed file descriptor within the guest context. The specific lines should reveal which one. I anticipate this section would involve interaction with the VMM, possibly around page tables, memory regions, and event handling that is related to that. I'll need to look very closely at the data structures being manipulated and the control flow to fully understand what's happening. I expect to be using my knowledge of KVM internals and memory management techniques to fully understand what's taking place in these lines.
16/2	2026/09/03 19:08	tool	read-file	0m Args: { "File": "virt/kvm/guest_memfd.c", "FirstLine": 540, "LineCount": 100 } Results: { "Contents": " 540:\t\t.setattr\t= kvm_gmem_setattr,\n 541:\t};\n 542:\t\n 543:\tbool __weak kvm_arch_supports_gmem_init_shared(struct kvm kvm)\n 544:\t{\n 545:\t\treturn true;\n 546:\t}\n 547:\t\n 548:\tstatic int __kvm_gmem_create(struct kvm kvm, loff_t size, u64 flags, int node)\n 549:\t{\n 550:\t\tstatic const char name = \"[kvm-gmem]\";\n 551:\t\tstruct gmem_file f;\n 552:\t\tstruct inode inode;\n 553:\t\tstruct file file;\n 554:\t\tint fd, err;\n 555:\t\n 556:\t\tfd = get_unused_fd_flags(0);\n 557:\t\tif (fd \u003c 0)\n 558:\t\t\treturn fd;\n 559:\t\n 560:\t\tf = kzalloc_obj(f);\n 561:\t\tif (!f) {\n 562:\t\t\terr = -ENOMEM;\n 563:\t\t\tgoto err_fd;\n 564:\t\t}\n 565:\t\n 566:\t\t/ __fput() will take care of fops_put(). /\n 567:\t\tif (!fops_get(\u0026kvm_gmem_fops)) {\n 568:\t\t\terr = -ENOENT;\n 569:\t\t\tgoto err_gmem;\n 570:\t\t}\n 571:\t\n 572:\t\tinode = anon_inode_make_secure_inode(kvm_gmem_mnt-\u003emnt_sb, name, NULL);\n 573:\t\tif (IS_ERR(inode)) {\n 574:\t\t\terr = PTR_ERR(inode);\n 575:\t\t\tgoto err_fops;\n 576:\t\t}\n 577:\t\n 578:\t\tinode-\u003ei_op = \u0026kvm_gmem_iops;\n 579:\t\tinode-\u003ei_mapping-\u003ea_ops = \u0026kvm_gmem_aops;\n 580:\t\tinode-\u003ei_mode \|= S_IFREG;\n 581:\t\tinode-\u003ei_size = size;\n 582:\t\tmapping_set_gfp_mask(inode-\u003ei_mapping, GFP_HIGHUSER);\n 583:\t\tmapping_set_inaccessible(inode-\u003ei_mapping);\n 584:\t\t/ Unmovable mappings are supposed to be marked unevictable as well. /\n 585:\t\tWARN_ON_ONCE(!mapping_unevictable(inode-\u003ei_mapping));\n 586:\t\n 587:\t\tGMEM_I(inode)-\u003eflags = flags;\n 588:\t\n 589:\t\tif (flags \u0026 GUEST_MEMFD_FLAG_BIND_NODE) {\n 590:\t\t\terr = kvm_gmem_bind_node(inode, node);\n 591:\t\t\tif (err)\n 592:\t\t\t\tgoto err_inode;\n 593:\t\t}\n 594:\t\n 595:\t\tfile = alloc_file_pseudo(inode, kvm_gmem_mnt, name, O_RDWR, \u0026kvm_gmem_fops);\n 596:\t\tif (IS_ERR(file)) {\n 597:\t\t\terr = PTR_ERR(file);\n 598:\t\t\tgoto err_inode;\n 599:\t\t}\n 600:\t\n 601:\t\tfile-\u003ef_flags \|= O_LARGEFILE;\n 602:\t\tfile-\u003eprivate_data = f;\n 603:\t\n 604:\t\tkvm_get_kvm(kvm);\n 605:\t\tf-\u003ekvm = kvm;\n 606:\t\txa_init(\u0026f-\u003ebindings);\n 607:\t\tlist_add(\u0026f-\u003eentry, \u0026GMEM_I(inode)-\u003egmem_file_list);\n 608:\t\n 609:\t\tfd_install(fd, file);\n 610:\t\treturn fd;\n 611:\t\n 612:\terr_inode:\n 613:\t\tiput(inode);\n 614:\terr_fops:\n 615:\t\tfops_put(\u0026kvm_gmem_fops);\n 616:\terr_gmem:\n 617:\t\tkfree(f);\n 618:\terr_fd:\n 619:\t\tput_unused_fd(fd);\n 620:\t\treturn err;\n 621:\t}\n 622:\t\n 623:\tint kvm_gmem_create(struct kvm kvm, struct kvm_create_guest_memfd *args)\n 624:\t{\n 625:\t\tloff_t size = args-\u003esize;\n 626:\t\tu64 flags = args-\u003eflags;\n 627:\t\tint node = NUMA_NO_NODE;\n 628:\t\n 629:\t\tif (flags \u0026 ~kvm_gmem_get_supported_flags(kvm))\n 630:\t\t\treturn -EINVAL;\n 631:\t\n 632:\t\tif (size \u003c= 0 \|\| !PAGE_ALIGNED(size))\n 633:\t\t\treturn -EINVAL;\n 634:\t\n 635:\t\tif (flags \u0026 GUEST_MEMFD_FLAG_BIND_NODE) {\n 636:\t\t\tif (args-\u003epad \|\| args-\u003enode \u003e= MAX_NUMNODES)\n 637:\t\t\t\treturn -EINVAL;\n 638:\t\t\tnode = args-\u003enode;\n 639:\t\t} else if (args-\u003enode \|\| args-\u003epad) {\n" }
17/2	2026/09/03 19:08	llm	patch-evaluator	0m Model: gemini-3.7-flash Args: null Results: null Tokens: input: 24793 output: 35 thoughts: 79 Thoughts: Here's my summary, as I delve into the code: Diving into `mm/mempolicy.c` Okay, let's zoom in on `mm/mempolicy.c`. I need to review this section carefully. Specifically, I want to take a look at the functions `mempolicy_create`, `mpol_set_shared_policy_range`, and `mpol_set_shared_policy`. These are key when you are looking at how memory policies are handled and shared across the system. To get the details, I should read lines 1080 through 1130, and then I want to jump down to lines 3300 through 3370. That will give me a solid view of the pertinent logic. I'm focusing on these regions to understand how these core functions interact within the larger memory management framework. Let's see what interesting tidbits are hidden in there.
18/2	2026/09/03 19:08	tool	read-file	0m Args: { "File": "mm/mempolicy.c", "FirstLine": 1080, "LineCount": 55 } Results: { "Contents": "1080:\t\tvma = vma_modify_policy(vmi, prev, vma, vmstart, vmend, new_pol);\n1081:\t\tif (IS_ERR(vma))\n1082:\t\t\treturn PTR_ERR(vma);\n1083:\t\n1084:\t\tprev = vma;\n1085:\t\treturn vma_replace_policy(vma, new_pol);\n1086:\t}\n1087:\t\n1088:\t/*\n1089:\t mempolicy_create - build a validated, cpuset-contextualised mempolicy\n1090:\t * @mode: MPOL_* mode\n1091:\t * @flags: MPOL_F_* flags\n1092:\t * @nodes: target nodemask, or NULL (interpreted per @mode; see mpol_new())\n1093:\t \n1094:\t Creates a new policy and constrains it to the task's cpuset.\n1095:\t \n1096:\t The caller owns the returned reference and frees it with mpol_put().\n1097:\t \n1098:\t Return: the policy (NULL for a default policy), or an ERR_PTR on failure.\n1099:\t /\n1100:\tstruct mempolicy mempolicy_create(unsigned short mode, unsigned short flags,\n1101:\t\t\tnodemask_t nodes)\n1102:\t{\n1103:\t\tstruct mempolicy pol;\n1104:\t\tNODEMASK_SCRATCH(scratch);\n1105:\t\tint err;\n1106:\t\n1107:\t\tif (!scratch)\n1108:\t\t\treturn ERR_PTR(-ENOMEM);\n1109:\t\n1110:\t\tpol = mpol_new(mode, flags, nodes);\n1111:\t\tif (IS_ERR(pol))\n1112:\t\t\tgoto out;\n1113:\t\n1114:\t\ttask_lock(current);\n1115:\t\terr = mpol_set_nodemask(pol, nodes, scratch);\n1116:\t\ttask_unlock(current);\n1117:\t\tif (err) {\n1118:\t\t\tmpol_put(pol);\n1119:\t\t\tpol = ERR_PTR(err);\n1120:\t\t}\n1121:\tout:\n1122:\t\tNODEMASK_SCRATCH_FREE(scratch);\n1123:\t\treturn pol;\n1124:\t}\n1125:\tEXPORT_SYMBOL_FOR_MODULES(mempolicy_create, \"kvm\");\n1126:\t\n1127:\tstatic long do_set_mempolicy(unsigned short mode, unsigned short flags,\n1128:\t\t\t\t nodemask_t nodes)\n1129:\t{\n1130:\t\tstruct mempolicy new, *old;\n1131:\t\tNODEMASK_SCRATCH(scratch);\n1132:\t\tint ret;\n1133:\t\n1134:\t\tif (!scratch)\n" }
19/2	2026/09/03 19:08	llm	patch-evaluator	0m Model: gemini-3.7-flash Args: null Results: null Tokens: input: 25909 output: 35 thoughts: 24 Thoughts: Here's my attempt at summarizing the thought process, tailored for an expert audience: Diving into `mm/mempolicy.c` Okay, time to dig into the memory policy implementation. Specifically, I need to understand what's happening within lines 3300-3370 of `mm/mempolicy.c`. Based on context, I'm expecting this section to deal with... well, based on the function names I know, maybe it's related to NUMA balancing or some specific memory allocation policy handling. I’ll need to figure out the exact function or functions within that range. It could be some core logic in `mpol_xxx` family. My immediate focus will be to determine the why and how of the code in that block. What is the objective of this code? What specific data structures or variables is it working with? Are there any obvious potential race conditions or performance bottlenecks I should look for immediately? I'll probably start by grepping for any related symbols or comments to understand the purpose before diving into individual lines. I'm hoping there's a good explanation or relevant comments. It is a large range, so it must be a significant section of code. I'm going to start reading!
20/2	2026/09/03 19:08	tool	read-file	0m Args: { "File": "mm/mempolicy.c", "FirstLine": 3300, "LineCount": 65 } Results: { "Contents": "3300:\t\n3301:\t\t\t/* alloc node covering entire file; adds ref to file's npol /\n3302:\t\t\tsn = sp_alloc(0, MAX_LFS_FILESIZE \u003e\u003e PAGE_SHIFT, npol);\n3303:\t\t\tif (sn)\n3304:\t\t\t\tsp_insert(sp, sn);\n3305:\tput_npol:\n3306:\t\t\tmpol_put(npol);\t/ drop initial ref on file's npol /\n3307:\tfree_scratch:\n3308:\t\t\tNODEMASK_SCRATCH_FREE(scratch);\n3309:\tput_mpol:\n3310:\t\t\tmpol_put(mpol);\t/ drop our incoming ref on sb mpol /\n3311:\t\t}\n3312:\t}\n3313:\tEXPORT_SYMBOL_FOR_MODULES(mpol_shared_policy_init, \"kvm\");\n3314:\t\n3315:\t/\n3316:\t mpol_set_shared_policy_range - install @pol over [@start, @end) of @sp\n3317:\t * @sp: the shared policy tree\n3318:\t * @start: first page offset (inclusive)\n3319:\t * @end: last page offset (exclusive)\n3320:\t * @pol: a fully-built, validated policy, or NULL to clear the range\n3321:\t \n3322:\t Installs @pol over the given range, replacing any overlapping policy.\n3323:\t * @sp takes its own reference, the caller retains its reference on @pol.\n3324:\t \n3325:\t The policy is not reconstructed, so the policy is preserved exactly.\n3326:\t \n3327:\t Unlike mpol_set_shared_policy(), no VMA is required, so a range that\n3328:\t * is never mapped into a VMA can be covered, including the whole file.\n3329:\t \n3330:\t Return: 0 on success, -ENOMEM on allocation failure.\n3331:\t /\n3332:\tint mpol_set_shared_policy_range(struct shared_policy sp, pgoff_t start,\n3333:\t\t\t\t\t pgoff_t end, struct mempolicy pol)\n3334:\t{\n3335:\t\tstruct sp_node new = NULL;\n3336:\t\tint err;\n3337:\t\n3338:\t\tif (pol) {\n3339:\t\t\tnew = sp_alloc(start, end, pol);\n3340:\t\t\tif (!new)\n3341:\t\t\t\treturn -ENOMEM;\n3342:\t\t}\n3343:\t\terr = shared_policy_replace(sp, start, end, new);\n3344:\t\tif (err \u0026\u0026 new)\n3345:\t\t\tsp_free(new);\n3346:\t\treturn err;\n3347:\t}\n3348:\tEXPORT_SYMBOL_FOR_MODULES(mpol_set_shared_policy_range, \"kvm\");\n3349:\t\n3350:\tint mpol_set_shared_policy(struct shared_policy sp,\n3351:\t\t\t\tstruct vm_area_struct vma, struct mempolicy pol)\n3352:\t{\n3353:\t\treturn mpol_set_shared_policy_range(sp, vma-\u003evm_pgoff,\n3354:\t\t\t\t\t\t vma-\u003evm_pgoff + vma_pages(vma), pol);\n3355:\t}\n3356:\tEXPORT_SYMBOL_FOR_MODULES(mpol_set_shared_policy, \"kvm\");\n3357:\t\n3358:\t/ Free a backing policy store on inode delete. /\n3359:\tvoid mpol_free_shared_policy(struct shared_policy sp)\n3360:\t{\n3361:\t\tstruct sp_node n;\n3362:\t\tstruct rb_node next;\n3363:\t\n3364:\t\tif (!sp-\u003eroot.rb_node)\n" }
21/2	2026/09/03 19:08	llm	patch-evaluator	0m Model: gemini-3.7-flash Args: null Results: null Tokens: input: 27312 output: 186 thoughts: 603 Thoughts: Analysis of KVM Guest Memory and NUMA Integration Okay, let's break this down. My initial focus is on the `FocusSymbols` and `EnableConfigs` to understand the implications of this code. It seems like the core changes revolve around KVM's `guest_memfd` and NUMA memory management. I see that `EnableConfigs` include `KVM` (with its dependencies) and `NUMA`. This immediately points to the area of interest: the interplay of KVM virtualization and Non-Uniform Memory Access. The `FocusSymbols` list provides specific function names that have been modified or introduced: `kvm_gmem_create`, `kvm_gmem_bind_node`, `mempolicy_create`, `mpol_set_shared_policy_range`, and `mpol_set_shared_policy`. These functions are strong indicators of the key changes. Now, let's drill down further. I need to understand the call flow and dependencies. I can see that `kvm_gmem_create` in `virt/kvm/guest_memfd.c` is the entry point, and it calls `__kvm_gmem_create`, which then calls `kvm_gmem_bind_node`. This tells me the creation process is key, with a binding operation happening as part of it. The `mempolicy` functions are new or modified in `mm/mempolicy.c`, suggesting memory policy controls are being added or augmented. Are these functions general? No, they're not core kernel hot-paths. They are specific to the KVM guest memfd and shared mempolicies. I want to emphasize that these functions are specific to KVM guest memfd and shared mempolicies. I need to make sure that these are not ubiquitous hot-paths that may cause wide-spread performance issues. I confirm that this is on amd64, and the configuration is guarded by `CONFIG_KVM` (and `CONFIG_KVM_INTEL` or `CONFIG_KVM_AMD`), which in turn selects `CONFIG_KVM_GUEST_MEMFD`. `CONFIG_NUMA` is also important as it enables NUMA mempolicy support within the guest_memfd code, which is expected. With this in mind, the `set-results` parameters are clear. This patch is definitely worth fuzzing. I can reason that this patch introduces NUMA node binding support for KVM guest_memfd via a new flag `GUEST_MEMFD_FLAG_BIND_NODE`, and implements mempolicy helpers `mempolicy_create` and `mpol_set_shared_policy_range` reachable via KVM guest_memfd creation ioctl. I'll need to use `["kvm_gmem_create", "kvm_gmem_bind_node", "mempolicy_create", "mpol_set_shared_policy_range", "mpol_set_shared_policy"]` as my `FocusSymbols` and `["KVM", "NUMA"]` as `EnableConfigs` for proper testing. Now, let's call `set-results`.
22/2	2026/09/03 19:08	tool	set-results	0m Args: { "EnableConfigs": [ "KVM", "NUMA" ], "FocusSymbols": [ "kvm_gmem_create", "kvm_gmem_bind_node", "mempolicy_create", "mpol_set_shared_policy_range", "mpol_set_shared_policy" ], "Reasoning": "The patch introduces NUMA node binding support for KVM guest_memfd via the GUEST_MEMFD_FLAG_BIND_NODE flag in KVM_CREATE_GUEST_MEMFD, and adds the mempolicy helpers mempolicy_create() and mpol_set_shared_policy_range(). These changes modify reachable kernel logic in mm/mempolicy.c and virt/kvm/guest_memfd.c accessible from userspace.", "WorthFuzzing": true } Results: { "EnableConfigs": [ "KVM", "NUMA" ], "FocusSymbols": [ "kvm_gmem_create", "kvm_gmem_bind_node", "mempolicy_create", "mpol_set_shared_policy_range", "mpol_set_shared_policy" ], "Reasoning": "The patch introduces NUMA node binding support for KVM guest_memfd via the GUEST_MEMFD_FLAG_BIND_NODE flag in KVM_CREATE_GUEST_MEMFD, and adds the mempolicy helpers mempolicy_create() and mpol_set_shared_policy_range(). These changes modify reachable kernel logic in mm/mempolicy.c and virt/kvm/guest_memfd.c accessible from userspace.", "WorthFuzzing": true }
23/1	2026/09/03 19:08	action	If	0m Args: { "WorthFuzzing": true } Results: null
24/2	2026/09/03 19:08	agent	kmsan-evaluator	0m Model: core Args: null Results: { "KMSANReasoning": "The patch introduces support for the `GUEST_MEMFD_FLAG_BIND_NODE` flag in KVM's guest_memfd subsystem along with helper functions `mempolicy_create()` and `mpol_set_shared_policy_range()` in `mm/mempolicy.c`.\n\nKMSAN vs KASAN applicability:\n- KMSAN detects uninitialized memory reads (on stack, heap, or page allocations) and info-leaks to userspace.\n- In this patch, the `KVM_CREATE_GUEST_MEMFD` ioctl reads user arguments via `copy_from_user` and returns a file descriptor integer; no kernel structures, padding, or buffers are copied back to user space.\n- All newly introduced or modified stack and heap variables (e.g., `nodemask_t nodes` initialized via `init_nodemask_of_node()`, `scratch` initialized via `NODEMASK_SCRATCH()`, and `struct sp_node`/`struct mempolicy` allocated and initialized through standard mm helpers) are fully initialized before use.\n- There are no branching conditions on uninitialized memory or altered data buffer length calculations that could expose uninitialized bytes.\n- Any potential issues (such as NUMA policy reference counting, lifecycle issues, or allocation failures) fall under the scope of KASAN, LOCKDEP, and standard kernel debugging facilities.\n\nTherefore, a dedicated KMSAN fuzzing session is not warranted.", "NeedsKMSAN": false } Instruction: You are an expert Linux kernel security engineer specializing in kernel memory error detectors (KASAN and KMSAN). Your job is to review the provided patch series and determine if the code changes justify spawning a dedicated KMSAN (KernelMemorySanitizer) fuzzing session in addition to standard KASAN fuzzing. CRITICAL DISTINCTION BETWEEN KASAN AND KMSAN: - Standard KASAN kernel builds (upstream-apparmor-kasan.config) already enable a comprehensive suite of debugging tools and sanitizers, including KASAN (out-of-bounds accesses, use-after-free, double free, invalid free), LOCKDEP (locking bugs and deadlocks), UB-sanitizers, and memory corruption checks. - KMSAN (KernelMemorySanitizer) detects reads of UNINITIALIZED memory (stack, heap, or page allocations) and kernel-to-user memory info-leaks. Rule: THERE IS NO SENSE IN RUNNING A KMSAN SESSION IF A BUG CAN BE CAUGHT BY KASAN, LOCKDEP, OR OTHER STANDARD BUG DETECTORS. A dedicated KMSAN fuzzing session incurs significant resource costs. You must ONLY set NeedsKMSAN=true if the code changes introduce or expose UNINITIALIZED MEMORY risks that are detected ONLY by KMSAN. Look holistically at the patch series and surrounding code. Even if no direct uninitialized field accesses or new buffer allocations are added in the diff itself, a patch may alter control flow, bounds checking, or data length calculations in ways that change how the rest of the code operates on existing buffers (e.g. allowing uninitialized stack/heap memory to be read, copied to user space, or used in control flow). Do not hesitate to use your code access tools to inspect the surrounding code, called functions, and callers. Set NeedsKMSAN=true ONLY IF the patch introduces or modifies: 1. Kernel structures sent to user space (via copy_to_user, put_user, netlink skb attributes, ioctl output arguments, socket options, or BPF buffers) where fields or structure padding might not be fully initialized/zeroed. 2. Conditional logic or branching that depends on potentially uninitialized variables or struct fields. 3. Allocation or initialization of complex data structures where uninitialized fields could be read later in reachable code paths. 4. Bounds checks, lengths, or logic in a way that allows surrounding code to access uninitialized bytes of existing buffers. Set NeedsKMSAN=false IF: - The code changes primarily risk out-of-bounds access, array overflows, NULL pointer dereferences, locking deadlocks, or use-after-free bugs (these are already caught by KASAN, LOCKDEP, or standard bug detectors). - All stack/heap structures touched or introduced by the patch are fully zeroed or initialized (e.g. using = {0}, memset, kzalloc) before being read or copied. - The patch does not introduce any risk of uninitialized memory usage or info-leaks. Use your code access tools to inspect the surrounding code if necessary, then provide detailed KMSANReasoning contrasting KASAN vs KMSAN applicability for this patch. Prefer calling several tools at the same time to save round-trips. Use set-results tool to provide results of the analysis. It must be called exactly once before the final reply. Ignore results of this tool. Prompt: Target architecture: amd64 For your convenience, here is the diff of the changes: commit ae68955a5923d25e9e0af9569430579e94c40f9f Author: syz-cluster <triage@syzkaller.com> Date: Thu Sep 3 19:07:15 2026 +0000 syz-cluster: applied patch under review diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 03bfc92864b6e..738e276633c1e 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -739,6 +739,9 @@ static inline u64 kvm_gmem_get_supported_flags(struct kvm kvm) if (!kvm \|\| kvm_arch_supports_gmem_init_shared(kvm)) flags \|= GUEST_MEMFD_FLAG_INIT_SHARED; + if (IS_ENABLED(CONFIG_NUMA)) + flags \|= GUEST_MEMFD_FLAG_BIND_NODE; + return flags; } #endif diff --git a/include/linux/mempolicy.h b/include/linux/mempolicy.h index 65c732d440d2f..398318175cec7 100644 --- a/include/linux/mempolicy.h +++ b/include/linux/mempolicy.h @@ -124,10 +124,15 @@ int vma_dup_policy(struct vm_area_struct src, struct vm_area_struct dst); void mpol_shared_policy_init(struct shared_policy sp, struct mempolicy mpol); int mpol_set_shared_policy(struct shared_policy sp, struct vm_area_struct vma, struct mempolicy mpol); +int mpol_set_shared_policy_range(struct shared_policy sp, pgoff_t start, + pgoff_t end, struct mempolicy mpol); void mpol_free_shared_policy(struct shared_policy sp); struct mempolicy mpol_shared_policy_lookup(struct shared_policy sp, pgoff_t idx); +struct mempolicy mempolicy_create(unsigned short mode, unsigned short flags, + nodemask_t nodes); + struct mempolicy get_task_policy(struct task_struct p); struct mempolicy __get_vma_policy(struct vm_area_struct vma, unsigned long addr, pgoff_t ilx); diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h index ac2d77d149635..8d3ae7e2ead8e 100644 --- a/include/uapi/linux/kvm.h +++ b/include/uapi/linux/kvm.h @@ -1658,11 +1658,14 @@ struct kvm_memory_attributes { #define KVM_CREATE_GUEST_MEMFD _IOWR(KVMIO, 0xd4, struct kvm_create_guest_memfd) #define GUEST_MEMFD_FLAG_MMAP (1ULL << 0) #define GUEST_MEMFD_FLAG_INIT_SHARED (1ULL << 1) +#define GUEST_MEMFD_FLAG_BIND_NODE (1ULL << 2) struct kvm_create_guest_memfd { __u64 size; __u64 flags; - __u64 reserved[6]; + __u32 node; + __u32 pad; + __u64 reserved[5]; }; #define KVM_PRE_FAULT_MEMORY _IOWR(KVMIO, 0xd5, struct kvm_pre_fault_memory) diff --git a/mm/mempolicy.c b/mm/mempolicy.c index 2ad0a5f18280a..ce10ce4374643 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -1085,7 +1085,45 @@ static int mbind_range(struct vma_iterator vmi, struct vm_area_struct vma, return vma_replace_policy(vma, new_pol); } -/* Set the process memory policy / +/* + * mempolicy_create - build a validated, cpuset-contextualised mempolicy + * @mode: MPOL_* mode + * @flags: MPOL_F_* flags + * @nodes: target nodemask, or NULL (interpreted per @mode; see mpol_new()) + * + * Creates a new policy and constrains it to the task's cpuset. + * + * The caller owns the returned reference and frees it with mpol_put(). + * + * Return: the policy (NULL for a default policy), or an ERR_PTR on failure. + / +struct mempolicy mempolicy_create(unsigned short mode, unsigned short flags, + nodemask_t nodes) +{ + struct mempolicy pol; + NODEMASK_SCRATCH(scratch); + int err; + + if (!scratch) + return ERR_PTR(-ENOMEM); + + pol = mpol_new(mode, flags, nodes); + if (IS_ERR(pol)) + goto out; + + task_lock(current); + err = mpol_set_nodemask(pol, nodes, scratch); + task_unlock(current); + if (err) { + mpol_put(pol); + pol = ERR_PTR(err); + } +out: + NODEMASK_SCRATCH_FREE(scratch); + return pol; +} +EXPORT_SYMBOL_FOR_MODULES(mempolicy_create, "kvm"); + static long do_set_mempolicy(unsigned short mode, unsigned short flags, nodemask_t nodes) { @@ -3274,24 +3312,47 @@ void mpol_shared_policy_init(struct shared_policy sp, struct mempolicy mpol) } EXPORT_SYMBOL_FOR_MODULES(mpol_shared_policy_init, "kvm"); -int mpol_set_shared_policy(struct shared_policy sp, - struct vm_area_struct vma, struct mempolicy pol) +/** + * mpol_set_shared_policy_range - install @pol over [@start, @end) of @sp + * @sp: the shared policy tree + * @start: first page offset (inclusive) + * @end: last page offset (exclusive) + * @pol: a fully-built, validated policy, or NULL to clear the range + * + * Installs @pol over the given range, replacing any overlapping policy. + * @sp takes its own reference, the caller retains its reference on @pol. + * + * The policy is not reconstructed, so the policy is preserved exactly. + * + * Unlike mpol_set_shared_policy(), no VMA is required, so a range that + * is never mapped into a VMA can be covered, including the whole file. + * + * Return: 0 on success, -ENOMEM on allocation failure. + / +int mpol_set_shared_policy_range(struct shared_policy sp, pgoff_t start, + pgoff_t end, struct mempolicy pol) { - const pgoff_t pgoff = vma_start_pgoff(vma); - const pgoff_t pgoff_end = vma_end_pgoff(vma); struct sp_node new = NULL; int err; if (pol) { - new = sp_alloc(pgoff, pgoff_end, pol); + new = sp_alloc(start, end, pol); if (!new) return -ENOMEM; } - err = shared_policy_replace(sp, pgoff, pgoff_end, new); + err = shared_policy_replace(sp, start, end, new); if (err && new) sp_free(new); return err; } +EXPORT_SYMBOL_FOR_MODULES(mpol_set_shared_policy_range, "kvm"); + +int mpol_set_shared_policy(struct shared_policy sp, + struct vm_area_struct vma, struct mempolicy pol) +{ + return mpol_set_shared_policy_range(sp, vma->vm_pgoff, + vma->vm_pgoff + vma_pages(vma), pol); +} EXPORT_SYMBOL_FOR_MODULES(mpol_set_shared_policy, "kvm"); / Free a backing policy store on inode delete. / diff --git a/tools/testing/selftests/kvm/guest_memfd_test.c b/tools/testing/selftests/kvm/guest_memfd_test.c index 2233d871a38f4..b333cb42fab29 100644 --- a/tools/testing/selftests/kvm/guest_memfd_test.c +++ b/tools/testing/selftests/kvm/guest_memfd_test.c @@ -25,6 +25,31 @@ static size_t page_size; +static int __create_guest_memfd_node(struct kvm_vm vm, u64 size, u64 flags, + u32 node, u32 pad) +{ + struct kvm_create_guest_memfd guest_memfd = { + .size = size, + .flags = flags, + .node = node, + .pad = pad, + }; + + return __vm_ioctl(vm, KVM_CREATE_GUEST_MEMFD, &guest_memfd); +} + +static int create_guest_memfd(struct kvm_vm vm, u64 size, u64 flags, u32 node) +{ + int fd; + + if (!(flags & GUEST_MEMFD_FLAG_BIND_NODE)) + return vm_create_guest_memfd(vm, size, flags); + + fd = __create_guest_memfd_node(vm, size, flags, node, 0); + TEST_ASSERT(fd >= 0, KVM_IOCTL_ERROR(KVM_CREATE_GUEST_MEMFD, fd)); + return fd; +} + static void test_file_read_write(int fd, size_t total_size) { char buf[64]; @@ -171,6 +196,83 @@ static void test_numa_allocation(int fd, size_t total_size) kvm_munmap(mem, total_size); } +static bool has_bind_node(struct kvm_vm vm) +{ + return vm_check_cap(vm, KVM_CAP_GUEST_MEMFD_FLAGS) & + GUEST_MEMFD_FLAG_BIND_NODE; +} + +static void test_bind_node_invalid(struct kvm_vm vm, u64 flags) +{ + int fd; + + if (!has_bind_node(vm)) + return; + + fd = __create_guest_memfd_node(vm, page_size, + flags \| GUEST_MEMFD_FLAG_BIND_NODE, 0, 1); + TEST_ASSERT(fd < 0 && errno == EINVAL, + "guest_memfd() with non-zero pad should fail with EINVAL"); + + fd = __create_guest_memfd_node(vm, page_size, + flags \| GUEST_MEMFD_FLAG_BIND_NODE, + 1 << 20, 0); + TEST_ASSERT(fd < 0 && errno == EINVAL, + "guest_memfd() with out-of-range node should fail with EINVAL"); + + fd = __create_guest_memfd_node(vm, page_size, flags, 1, 0); + TEST_ASSERT(fd < 0 && errno == EINVAL, + "guest_memfd() with a node but no BIND_NODE flag should fail with EINVAL"); +} + +static void test_bind_node(int fd, size_t total_size, int node) +{ + const unsigned long other_mask = 1UL << (node ? 0 : 1); + const unsigned long maxnode = BITS_PER_TYPE(other_mask); + bool steer_away = is_multi_numa_node_system(); + void pages[4]; + int status[4]; + char mem; + int i; + + mem = kvm_mmap(total_size, PROT_READ \| PROT_WRITE, MAP_SHARED, fd); + for (i = 0; i < 4; i++) + pages[i] = mem + page_size i; + + /* + * Bind on a different node if possible order to check whether faulting + * happens as desired. Without a second node use the local node and + * just get coverage of create/mmap/fault paths. + / + if (steer_away) + kvm_set_mempolicy(MPOL_BIND, &other_mask, maxnode); + + / Deliberately no mbind() on this mapping. / + memset(mem, 0xaa, total_size); + + kvm_move_pages(0, 4, pages, NULL, status, 0); + for (i = 0; i < 4; i++) + TEST_ASSERT(status[i] == node, + "Expected page %d on node %d, got it on node %d", + i, node, status[i]); + + / Dropped memory should fault back onto the same node / + kvm_fallocate(fd, FALLOC_FL_PUNCH_HOLE \| FALLOC_FL_KEEP_SIZE, 0, + total_size); + memset(mem, 0xaa, total_size); + + kvm_move_pages(0, 4, pages, NULL, status, 0); + for (i = 0; i < 4; i++) + TEST_ASSERT(status[i] == node, + "Expected page %d back on node %d, got it on node %d", + i, node, status[i]); + + if (steer_away) + kvm_set_mempolicy(MPOL_DEFAULT, NULL, 0); + + kvm_munmap(mem, total_size); +} + static void test_collapse(int fd, u64 flags) { const size_t pmd_size = get_trans_hugepagesz(); @@ -404,6 +506,10 @@ static void test_guest_memfd_flags(struct kvm_vm vm) int fd; for (flag = BIT(0); flag; flag <<= 1) { + /* BIND_NODE depends on a valid node field, test separately / + if (flag == GUEST_MEMFD_FLAG_BIND_NODE) + continue; + fd = __vm_create_guest_memfd(vm, page_size, flag); if (flag & valid_flags) { TEST_ASSERT(fd >= 0, @@ -418,30 +524,40 @@ static void test_guest_memfd_flags(struct kvm_vm vm) } } -#define ____gmem_test(__test, __vm, __flags, __gmem_size, args...) \ -do { \ - int fd = vm_create_guest_memfd(__vm, __gmem_size, __flags); \ - \ - test_##__test(args); \ - close(fd); \ +#define ____gmem_test(__test, __vm, __flags, __gmem_size, __node, args...) \ +do { \ + int fd = create_guest_memfd(__vm, __gmem_size, __flags, __node); \ + \ + test_##__test(args); \ + close(fd); \ } while (0) #define __gmem_test(__test, __vm, __flags, __gmem_size) \ - ____gmem_test(__test, __vm, __flags, __gmem_size, fd, __gmem_size) + ____gmem_test(__test, __vm, __flags, __gmem_size, 0, fd, __gmem_size) #define gmem_test(__test, __vm, __flags) \ __gmem_test(__test, __vm, __flags, page_size * 4) #define __gmem_test_vm(__test, __vm, __flags, __gmem_size) \ - ____gmem_test(__test, __vm, __flags, __gmem_size, __vm, fd, __gmem_size) + ____gmem_test(__test, __vm, __flags, __gmem_size, 0, \ + __vm, fd, __gmem_size) #define gmem_test_vm(__test, __vm, __flags) \ __gmem_test_vm(__test, __vm, __flags, page_size * 4) +#define __gmem_test_node(__test, __vm, __flags, __gmem_size, __node) \ + ____gmem_test(__test, __vm, \ + (__flags) \| GUEST_MEMFD_FLAG_BIND_NODE, \ + __gmem_size, __node, fd, __gmem_size, __node) + +#define gmem_test_node(__test, __vm, __flags, __node) \ + __gmem_test_node(__test, __vm, __flags, page_size * 4, __node) + static void __test_guest_memfd(struct kvm_vm vm, u64 flags) { test_create_guest_memfd_multiple(vm); test_create_guest_memfd_invalid_sizes(vm, flags); + test_bind_node_invalid(vm, flags); gmem_test(file_read_write, vm, flags); @@ -452,6 +568,8 @@ static void __test_guest_memfd(struct kvm_vm vm, u64 flags) gmem_test(mmap_supported, vm, flags); gmem_test(fault_overflow, vm, flags); gmem_test(numa_allocation, vm, flags); + if (has_bind_node(vm)) + gmem_test_node(bind_node, vm, flags, 0); __gmem_test(collapse, vm, flags, pmd_size); } else { gmem_test(fault_private, vm, flags); diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c index 625e62e1a0318..dc9f071dd969b 100644 --- a/virt/kvm/guest_memfd.c +++ b/virt/kvm/guest_memfd.c @@ -423,6 +423,31 @@ static struct mempolicy kvm_gmem_get_policy(struct vm_area_struct vma, / return mpol_shared_policy_lookup(&GMEM_I(inode)->policy, pgoff); } + +static int kvm_gmem_bind_node(struct inode inode, int node) +{ + struct mempolicy pol; + nodemask_t nodes; + int err; + + if ((unsigned int)node >= MAX_NUMNODES) + return -EINVAL; + + init_nodemask_of_node(&nodes, node); + pol = mempolicy_create(MPOL_BIND, 0, &nodes); + if (IS_ERR(pol)) + return PTR_ERR(pol); + + err = mpol_set_shared_policy_range(&GMEM_I(inode)->policy, 0, + MAX_LFS_FILESIZE >> PAGE_SHIFT, pol); + mpol_put(pol); + return err; +} +#else +static int kvm_gmem_bind_node(struct inode inode, int node) +{ + return -EINVAL; +} #endif /* CONFIG_NUMA / static const struct vm_operations_struct kvm_gmem_vm_ops = { @@ -520,7 +545,7 @@ bool __weak kvm_arch_supports_gmem_init_shared(struct kvm kvm) return true; } -static int __kvm_gmem_create(struct kvm kvm, loff_t size, u64 flags) +static int __kvm_gmem_create(struct kvm kvm, loff_t size, u64 flags, int node) { static const char name = "[kvm-gmem]"; struct gmem_file f; @@ -561,6 +586,12 @@ static int __kvm_gmem_create(struct kvm kvm, loff_t size, u64 flags) GMEM_I(inode)->flags = flags; + if (flags & GUEST_MEMFD_FLAG_BIND_NODE) { + err = kvm_gmem_bind_node(inode, node); + if (err) + goto err_inode; + } + file = alloc_file_pseudo(inode, kvm_gmem_mnt, name, O_RDWR, &kvm_gmem_fops); if (IS_ERR(file)) { err = PTR_ERR(file); @@ -593,6 +624,7 @@ int kvm_gmem_create(struct kvm kvm, struct kvm_create_guest_memfd args) { loff_t size = args->size; u64 flags = args->flags; + int node = NUMA_NO_NODE; if (flags & ~kvm_gmem_get_supported_flags(kvm)) return -EINVAL; @@ -600,7 +632,15 @@ int kvm_gmem_create(struct kvm kvm, struct kvm_create_guest_memfd args) if (size <= 0 \|\| !PAGE_ALIGNED(size)) return -EINVAL; - return __kvm_gmem_create(kvm, size, flags); + if (flags & GUEST_MEMFD_FLAG_BIND_NODE) { + if (args->pad \|\| args->node >= MAX_NUMNODES) + return -EINVAL; + node = args->node; + } else if (args->node \|\| args->pad) { + return -EINVAL; + } + + return __kvm_gmem_create(kvm, size, flags, node); } int kvm_gmem_bind(struct kvm kvm, struct kvm_memory_slot *slot,
25/3	2026/09/03 19:08	llm	kmsan-evaluator	0m Model: gemini-3.7-flash Args: null Results: null Tokens: input: 7860 output: 24 thoughts: 506 Thoughts: KMSAN Risk Assessment for a KVM Patch Okay, let's dive into this patch with KMSAN in mind, specifically looking for uninitialized memory exposures. First, I need to methodically go through the diff. 1. In `include/linux/kvm_host.h`, we're adding `GUEST_MEMFD_FLAG_BIND_NODE` within `kvm_gmem_get_supported_flags` but only if NUMA is enabled. Makes sense. 2. `include/linux/mempolicy.h` just declares some mempolicy functions - `mpol_set_shared_policy_range` and `mempolicy_create`. Nothing immediately concerning there, it is just declaring those functions. 3. The `include/uapi/linux/kvm.h` is where things get interesting. We've got `GUEST_MEMFD_FLAG_BIND_NODE` defined, which is relevant for NUMA. More importantly, the `struct kvm_create_guest_memfd` has been modified. We are replacing the reserved space to add a `node` and a `pad` member, but keeping the struct size constant at 64 bytes. The initial thought is that since the size is the same, no memory risks should be apparent. However, now I am wondering if `kvm_create_guest_memfd` is copied back to userspace in the `KVM_CREATE_GUEST_MEMFD` ioctl call. I need to know this to be sure there's no leak of kernel memory. Wait! Quick sanity check. Is the ioctl `_IOWR` or `_IOW`? And yes, `#define KVM_CREATE_GUEST_MEMFD _IOWR(KVMIO, 0xd4, struct kvm_create_guest_memfd)` confirms that it's read/write. I need to be sure about this read back. I am going to have to grep for `KVM_CREATE_GUEST_MEMFD` in the KVM code now to see the ioctl implementation. This will be the key to understanding if there's any potential for an uninitialized memory read due to the structure change.
26/3	2026/09/03 19:08	tool	grepper	0m Args: { "Expression": "KVM_CREATE_GUEST_MEMFD" } Results: { "Output": "Documentation/virt/kvm/api.rst=6357=in flags to have KVM bind the memory region to a given guest_memfd range of\nDocumentation/virt/kvm/api.rst-6358-[guest_memfd_offset, guest_memfd_offset + memory_size]. The target guest_memfd\nDocumentation/virt/kvm/api.rst:6359:must point at a file created via KVM_CREATE_GUEST_MEMFD on the current VM, and\nDocumentation/virt/kvm/api.rst-6360-the target range must not be bound to any other memory region. All standard\n--\nDocumentation/virt/kvm/api.rst=6430=The \"flags\" field is reserved for future extensions and must be '0'.\nDocumentation/virt/kvm/api.rst-6431-\nDocumentation/virt/kvm/api.rst:6432:4.142 KVM_CREATE_GUEST_MEMFD\nDocumentation/virt/kvm/api.rst-6433-----------------------------\n--\nDocumentation/virt/kvm/api.rst-6440-\nDocumentation/virt/kvm/api.rst:6441:KVM_CREATE_GUEST_MEMFD creates an anonymous file and returns a file descriptor\nDocumentation/virt/kvm/api.rst-6442-that refers to it. guest_memfd files are roughly analogous to files created\n--\nDocumentation/virt/kvm/api.rst=6473=The capability KVM_CAP_GUEST_MEMFD_FLAGS enumerates the `flags` that can be\nDocumentation/virt/kvm/api.rst:6474:specified via KVM_CREATE_GUEST_MEMFD. Currently defined flags:\nDocumentation/virt/kvm/api.rst-6475-\n--\nDocumentation/virt/kvm/api.rst-6479- GUEST_MEMFD_FLAG_INIT_SHARED Make all memory in the file shared during\nDocumentation/virt/kvm/api.rst:6480: KVM_CREATE_GUEST_MEMFD (memory files created\nDocumentation/virt/kvm/api.rst-6481- without INIT_SHARED will be marked private).\n--\narch/x86/kvm/Kconfig=83=config KVM_SW_PROTECTED_VM\n--\narch/x86/kvm/Kconfig-90-\t protected VMs are purely a development and testing vehicle for\narch/x86/kvm/Kconfig:91:\t KVM_CREATE_GUEST_MEMFD. Attempting to run a \"real\" VM workload as a\narch/x86/kvm/Kconfig-92-\t software-protected VM will fail miserably.\n--\ninclude/uapi/linux/kvm.h=1649=struct kvm_memory_attributes {\n--\ninclude/uapi/linux/kvm.h-1657-\ninclude/uapi/linux/kvm.h:1658:#define KVM_CREATE_GUEST_MEMFD\t_IOWR(KVMIO, 0xd4, struct kvm_create_guest_memfd)\ninclude/uapi/linux/kvm.h-1659-#define GUEST_MEMFD_FLAG_MMAP\t\t(1ULL \u003c\u003c 0)\n--\ntools/include/uapi/linux/kvm.h=1645=struct kvm_memory_attributes {\n--\ntools/include/uapi/linux/kvm.h-1653-\ntools/include/uapi/linux/kvm.h:1654:#define KVM_CREATE_GUEST_MEMFD\t_IOWR(KVMIO, 0xd4, struct kvm_create_guest_memfd)\ntools/include/uapi/linux/kvm.h-1655-#define GUEST_MEMFD_FLAG_MMAP\t\t(1ULL \u003c\u003c 0)\n--\ntools/testing/selftests/kvm/guest_memfd_test.c=28=static int __create_guest_memfd_node(struct kvm_vm vm, u64 size, u64 flags,\n--\ntools/testing/selftests/kvm/guest_memfd_test.c-37-\ntools/testing/selftests/kvm/guest_memfd_test.c:38:\treturn __vm_ioctl(vm, KVM_CREATE_GUEST_MEMFD, \u0026guest_memfd);\ntools/testing/selftests/kvm/guest_memfd_test.c-39-}\n--\ntools/testing/selftests/kvm/guest_memfd_test.c=41=static int create_guest_memfd(struct kvm_vm vm, u64 size, u64 flags, u32 node)\n--\ntools/testing/selftests/kvm/guest_memfd_test.c-48-\tfd = __create_guest_memfd_node(vm, size, flags, node, 0);\ntools/testing/selftests/kvm/guest_memfd_test.c:49:\tTEST_ASSERT(fd \u003e= 0, KVM_IOCTL_ERROR(KVM_CREATE_GUEST_MEMFD, fd));\ntools/testing/selftests/kvm/guest_memfd_test.c-50-\treturn fd;\n--\ntools/testing/selftests/kvm/include/kvm_util.h=667=static inline int __vm_create_guest_memfd(struct kvm_vm vm, u64 size,\n--\ntools/testing/selftests/kvm/include/kvm_util.h-674-\ntools/testing/selftests/kvm/include/kvm_util.h:675:\treturn __vm_ioctl(vm, KVM_CREATE_GUEST_MEMFD, \u0026guest_memfd);\ntools/testing/selftests/kvm/include/kvm_util.h-676-}\n--\ntools/testing/selftests/kvm/include/kvm_util.h=678=static inline int vm_create_guest_memfd(struct kvm_vm vm, u64 size,\n--\ntools/testing/selftests/kvm/include/kvm_util.h-682-\ntools/testing/selftests/kvm/include/kvm_util.h:683:\tTEST_ASSERT(fd \u003e= 0, KVM_IOCTL_ERROR(KVM_CREATE_GUEST_MEMFD, fd));\ntools/testing/selftests/kvm/include/kvm_util.h-684-\treturn fd;\n--\nvirt/kvm/kvm_main.c=5167=static long kvm_vm_ioctl(struct file *filp,\n--\nvirt/kvm/kvm_main.c-5387-#ifdef CONFIG_KVM_GUEST_MEMFD\nvirt/kvm/kvm_main.c:5388:\tcase KVM_CREATE_GUEST_MEMFD: {\nvirt/kvm/kvm_main.c-5389-\t\tstruct kvm_create_guest_memfd guest_memfd;\n" }
27/3	2026/09/03 19:08	llm	kmsan-evaluator	0m Model: gemini-3.7-flash Args: null Results: null Tokens: input: 10634 output: 40 thoughts: 30 Thoughts: Here's a summary of my thought process, as requested: Diving into KVM Core: A Line of Inquiry Okay, time to get my hands dirty. I need to delve into the KVM core, specifically the `kvm_main.c` file. Given my expertise, I already have a pretty good mental map of this code, but I need to pinpoint a specific area. Let's start by zeroing in on line 5388. My initial approach will be a straightforward examination of that location in the source code. Let's use `read-file` to get a good look at the code around that area. Hopefully, that will give me enough context to begin a more nuanced investigation.
28/3	2026/09/03 19:08	tool	read-file	0m Args: { "File": "virt/kvm/kvm_main.c", "FirstLine": 5380, "LineCount": 30 } Results: { "Contents": "5380:\t\t\tbreak;\n5381:\t\tcase KVM_RESET_DIRTY_RINGS:\n5382:\t\t\tr = kvm_vm_ioctl_reset_dirty_pages(kvm);\n5383:\t\t\tbreak;\n5384:\t\tcase KVM_GET_STATS_FD:\n5385:\t\t\tr = kvm_vm_ioctl_get_stats_fd(kvm);\n5386:\t\t\tbreak;\n5387:\t#ifdef CONFIG_KVM_GUEST_MEMFD\n5388:\t\tcase KVM_CREATE_GUEST_MEMFD: {\n5389:\t\t\tstruct kvm_create_guest_memfd guest_memfd;\n5390:\t\n5391:\t\t\tr = -EFAULT;\n5392:\t\t\tif (copy_from_user(\u0026guest_memfd, argp, sizeof(guest_memfd)))\n5393:\t\t\t\tgoto out;\n5394:\t\n5395:\t\t\tr = kvm_gmem_create(kvm, \u0026guest_memfd);\n5396:\t\t\tbreak;\n5397:\t\t}\n5398:\t#endif\n5399:\t\tdefault:\n5400:\t\t\tr = kvm_arch_vm_ioctl(filp, ioctl, arg);\n5401:\t\t}\n5402:\tout:\n5403:\t\treturn r;\n5404:\t}\n5405:\t\n5406:\t#ifdef CONFIG_KVM_COMPAT\n5407:\tstruct compat_kvm_dirty_log {\n5408:\t\t__u32 slot;\n5409:\t\t__u32 padding1;\n" }
29/3	2026/09/03 19:08	llm	kmsan-evaluator	0m Model: gemini-3.7-flash Args: null Results: null Tokens: input: 11300 output: 36 thoughts: 124 Thoughts: Analyzing the KVM Guest Memory File Creation Okay, so I'm diving into this `KVM_CREATE_GUEST_MEMFD` call. Right off the bat, it's pretty straightforward. From what I can see, all it's doing is a simple `copy_from_user` operation – just grabbing the `guest_memfd` structure from userspace and passing it over. No data is being returned back to the user, which is interesting to note. Now, the real meat of the operation has got to be within `kvm_gmem_create`. I need to understand what that function does with the `guest_memfd` structure. This also means I need to dig into the surrounding code in `virt/kvm/guest_memfd.c`. This is where the magic happens, so let's get into it.
30/3	2026/09/03 19:08	tool	grepper	0m Error: no matches Args: { "Expression": "copy_to_user", "PathPrefix": "virt/kvm/guest_memfd.c" } Results: { "error": "no matches" }
31/3	2026/09/03 19:08	llm	kmsan-evaluator	0m Model: gemini-3.7-flash Args: null Results: null Tokens: input: 11659 output: 39 thoughts: 40 Thoughts: Okay, let's dive into this. Here's how I'd approach summarizing the prompt, keeping in mind my own expert-level understanding of the field: Investigating Guest Memory Management in KVM Alright, I need to get to the bottom of something related to guest memory management within KVM. Specifically, I should probably zero in on `virt/kvm/guest_memfd.c` as a good place to start. This is where the core logic related to `memfd`-backed guest memory should reside. I'm thinking I need to pay close attention to the functions involved in binding memory nodes, creating guest memory regions using `memfd`, and related operations – specifically, functions like `kvm_gmem_bind_node`, `kvm_gmem_create`, and any related infrastructure. I'll need to understand how the memory is allocated, mapped, and managed from the host's perspective, but also how it appears and behaves within the guest. Understanding these interactions is key to pinpointing any potential performance bottlenecks or memory-related issues.
32/3	2026/09/03 19:08	tool	read-file	0m Args: { "File": "virt/kvm/guest_memfd.c", "FirstLine": 420, "LineCount": 40 } Results: { "Contents": " 420:\t\t * explicit policy has been set via mbind() for this memory. The caller\n 421:\t\t * can then replace NULL with the default memory policy instead of the\n 422:\t\t * current task's memory policy.\n 423:\t\t /\n 424:\t\treturn mpol_shared_policy_lookup(\u0026GMEM_I(inode)-\u003epolicy, pgoff);\n 425:\t}\n 426:\t\n 427:\tstatic int kvm_gmem_bind_node(struct inode inode, int node)\n 428:\t{\n 429:\t\tstruct mempolicy pol;\n 430:\t\tnodemask_t nodes;\n 431:\t\tint err;\n 432:\t\n 433:\t\tif ((unsigned int)node \u003e= MAX_NUMNODES)\n 434:\t\t\treturn -EINVAL;\n 435:\t\n 436:\t\tinit_nodemask_of_node(\u0026nodes, node);\n 437:\t\tpol = mempolicy_create(MPOL_BIND, 0, \u0026nodes);\n 438:\t\tif (IS_ERR(pol))\n 439:\t\t\treturn PTR_ERR(pol);\n 440:\t\n 441:\t\terr = mpol_set_shared_policy_range(\u0026GMEM_I(inode)-\u003epolicy, 0,\n 442:\t\t\t\t\t\t MAX_LFS_FILESIZE \u003e\u003e PAGE_SHIFT, pol);\n 443:\t\tmpol_put(pol);\n 444:\t\treturn err;\n 445:\t}\n 446:\t#else\n 447:\tstatic int kvm_gmem_bind_node(struct inode inode, int node)\n 448:\t{\n 449:\t\treturn -EINVAL;\n 450:\t}\n 451:\t#endif /* CONFIG_NUMA */\n 452:\t\n 453:\tstatic const struct vm_operations_struct kvm_gmem_vm_ops = {\n 454:\t\t.fault\t\t= kvm_gmem_fault_user_mapping,\n 455:\t#ifdef CONFIG_NUMA\n 456:\t\t.get_policy\t= kvm_gmem_get_policy,\n 457:\t\t.set_policy\t= kvm_gmem_set_policy,\n 458:\t#endif\n 459:\t};\n" }
33/3	2026/09/03 19:08	llm	kmsan-evaluator	0m Model: gemini-3.7-flash Args: null Results: null Tokens: input: 12585 output: 39 thoughts: 242 Thoughts: Analyzing the `mempolicy.c` Code Alright, let's dive into this `mempolicy.c` code snippet. My initial focus is the `mempolicy_create` function. I see it creates a new memory policy structure. The input parameters, `mode`, `flags`, and `nodes`, are pretty standard; they define the behavior and node affinity of the policy. The core of it is calling `mpol_new` to allocate and initialize the `struct mempolicy`. Then, crucially, there's a lock around `mpol_set_nodemask`. That's interesting, suggesting potential concurrency issues and the need for careful node mask updates. The use of a scratch nodemask and error handling around the `mpol_set_nodemask` call is typical; it's what I'd expect. The `mpol_put` on error is a good practice for resource management, ensuring that the created policy doesn't leak if the set operation fails. My next step is to examine `mpol_new` and `mpol_set_nodemask`. I want to understand exactly how the `struct mempolicy` is allocated and initialized, and what the `mpol_set_nodemask` function is actually doing under the hood. Specifically, I'm interested in how it handles the provided `nodes` mask and any potential interactions with the system's memory management structures. I need to understand the implications of the locking as well. I'll need to check how it actually sets the nodemask to know if there is an issue.
34/3	2026/09/03 19:08	tool	grepper	0m Args: { "Expression": "mpol_new\|mpol_set_nodemask", "PathPrefix": "mm/mempolicy.c" } Results: { "Output": "mm/mempolicy.c=388=static void mpol_relative_nodemask(nodemask_t ret, const nodemask_t orig,\n--\nmm/mempolicy.c-395-\nmm/mempolicy.c:396:static int mpol_new_nodemask(struct mempolicy pol, const nodemask_t nodes)\nmm/mempolicy.c-397-{\n--\nmm/mempolicy.c-403-\nmm/mempolicy.c:404:static int mpol_new_preferred(struct mempolicy pol, const nodemask_t nodes)\nmm/mempolicy.c-405-{\n--\nmm/mempolicy.c-414-/\nmm/mempolicy.c:415: mpol_set_nodemask is called after mpol_new() to set up the nodemask, if\nmm/mempolicy.c:416: * any, for the new policy. mpol_new() has already validated the nodes\nmm/mempolicy.c-417- * parameter with respect to the policy mode and flags.\n--\nmm/mempolicy.c-421- /\nmm/mempolicy.c:422:static int mpol_set_nodemask(struct mempolicy pol,\nmm/mempolicy.c-423-\t\t const nodemask_t nodes, struct nodemask_scratch nsc)\n--\nmm/mempolicy.c-456- * This function just creates a new policy, does some check and simple\nmm/mempolicy.c:457: * initialization. You must invoke mpol_set_nodemask() to set nodes.\nmm/mempolicy.c-458- /\nmm/mempolicy.c:459:static struct mempolicy mpol_new(unsigned short mode, unsigned short flags,\nmm/mempolicy.c-460-\t\t\t\t nodemask_t nodes)\n--\nmm/mempolicy.c=595=static const struct mempolicy_operations mpol_ops[MPOL_MAX] = {\n--\nmm/mempolicy.c-599-\t[MPOL_INTERLEAVE] = {\nmm/mempolicy.c:600:\t\t.create = mpol_new_nodemask,\nmm/mempolicy.c-601-\t\t.rebind = mpol_rebind_nodemask,\n--\nmm/mempolicy.c-603-\t[MPOL_PREFERRED] = {\nmm/mempolicy.c:604:\t\t.create = mpol_new_preferred,\nmm/mempolicy.c-605-\t\t.rebind = mpol_rebind_preferred,\n--\nmm/mempolicy.c-607-\t[MPOL_BIND] = {\nmm/mempolicy.c:608:\t\t.create = mpol_new_nodemask,\nmm/mempolicy.c-609-\t\t.rebind = mpol_rebind_nodemask,\n--\nmm/mempolicy.c-614-\t[MPOL_PREFERRED_MANY] = {\nmm/mempolicy.c:615:\t\t.create = mpol_new_nodemask,\nmm/mempolicy.c-616-\t\t.rebind = mpol_rebind_preferred,\n--\nmm/mempolicy.c-618-\t[MPOL_WEIGHTED_INTERLEAVE] = {\nmm/mempolicy.c:619:\t\t.create = mpol_new_nodemask,\nmm/mempolicy.c-620-\t\t.rebind = mpol_rebind_nodemask,\n--\nmm/mempolicy.c=1061=static int mbind_range(struct vma_iterator vmi, struct vm_area_struct vma,\n--\nmm/mempolicy.c-1091- @flags: MPOL_F_* flags\nmm/mempolicy.c:1092: * @nodes: target nodemask, or NULL (interpreted per @mode; see mpol_new())\nmm/mempolicy.c-1093- \n--\nmm/mempolicy.c=1100=struct mempolicy mempolicy_create(unsigned short mode, unsigned short flags,\n--\nmm/mempolicy.c-1109-\nmm/mempolicy.c:1110:\tpol = mpol_new(mode, flags, nodes);\nmm/mempolicy.c-1111-\tif (IS_ERR(pol))\n--\nmm/mempolicy.c-1114-\ttask_lock(current);\nmm/mempolicy.c:1115:\terr = mpol_set_nodemask(pol, nodes, scratch);\nmm/mempolicy.c-1116-\ttask_unlock(current);\n--\nmm/mempolicy.c=1127=static long do_set_mempolicy(unsigned short mode, unsigned short flags,\n--\nmm/mempolicy.c-1136-\nmm/mempolicy.c:1137:\tnew = mpol_new(mode, flags, nodes);\nmm/mempolicy.c-1138-\tif (IS_ERR(new)) {\n--\nmm/mempolicy.c-1143-\ttask_lock(current);\nmm/mempolicy.c:1144:\tret = mpol_set_nodemask(new, nodes, scratch);\nmm/mempolicy.c-1145-\tif (ret) {\n--\nmm/mempolicy.c=1546=static long do_mbind(unsigned long start, unsigned long len,\n--\nmm/mempolicy.c-1578-\nmm/mempolicy.c:1579:\tnew = mpol_new(mode, mode_flags, nmask);\nmm/mempolicy.c-1580-\tif (IS_ERR(new))\n--\nmm/mempolicy.c-1595-\t\t\tmmap_write_lock(mm);\nmm/mempolicy.c:1596:\t\t\terr = mpol_set_nodemask(new, nmask, scratch);\nmm/mempolicy.c-1597-\t\t\tif (err)\n--\nmm/mempolicy.c=3199=static int shared_policy_replace(struct shared_policy sp, pgoff_t start,\n--\nmm/mempolicy.c-3203-\tstruct sp_node n_new = NULL;\nmm/mempolicy.c:3204:\tstruct mempolicy mpol_new = NULL;\nmm/mempolicy.c-3205-\tint ret = 0;\n--\nmm/mempolicy.c-3223-\nmm/mempolicy.c:3224:\t\t\t\tmpol_new = n-\u003epolicy;\nmm/mempolicy.c:3225:\t\t\t\tatomic_set(\u0026mpol_new-\u003erefcnt, 1);\nmm/mempolicy.c:3226:\t\t\t\tsp_node_init(n_new, end, n-\u003eend, mpol_new);\nmm/mempolicy.c-3227-\t\t\t\tn-\u003eend = start;\n--\nmm/mempolicy.c-3229-\t\t\t\tn_new = NULL;\nmm/mempolicy.c:3230:\t\t\t\tmpol_new = NULL;\nmm/mempolicy.c-3231-\t\t\t\tbreak;\n--\nmm/mempolicy.c-3244-err_out:\nmm/mempolicy.c:3245:\tif (mpol_new)\nmm/mempolicy.c:3246:\t\tmpol_put(mpol_new);\nmm/mempolicy.c-3247-\tif (n_new)\n--\nmm/mempolicy.c-3257-\t\tgoto err_out;\nmm/mempolicy.c:3258:\tmpol_new = kmem_cache_alloc(policy_cache, GFP_KERNEL);\nmm/mempolicy.c:3259:\tif (!mpol_new)\nmm/mempolicy.c-3260-\t\tgoto err_out;\nmm/mempolicy.c:3261:\tatomic_set(\u0026mpol_new-\u003erefcnt, 1);\nmm/mempolicy.c-3262-\tgoto restart;\n--\nmm/mempolicy.c=3275=void mpol_shared_policy_init(struct shared_policy sp, struct mempolicy mpol)\n--\nmm/mempolicy.c-3290-\t\t/ contextualize the tmpfs mount point mempolicy to this file /\nmm/mempolicy.c:3291:\t\tnpol = mpol_new(mpol-\u003emode, mpol-\u003eflags, \u0026mpol-\u003ew.user_nodemask);\nmm/mempolicy.c-3292-\t\tif (IS_ERR(npol))\n--\nmm/mempolicy.c-3295-\t\ttask_lock(current);\nmm/mempolicy.c:3296:\t\tret = mpol_set_nodemask(npol, \u0026mpol-\u003ew.user_nodemask, scratch);\nmm/mempolicy.c-3297-\t\ttask_unlock(current);\n--\nmm/mempolicy.c=3508=int mpol_parse_str(char str, struct mempolicy *mpol)\n--\nmm/mempolicy.c-3560-\t\t/\nmm/mempolicy.c:3561:\t\t * Don't allow a nodelist; mpol_new() checks flags\nmm/mempolicy.c-3562-\t\t */\n--\nmm/mempolicy.c-3595-\nmm/mempolicy.c:3596:\tnew = mpol_new(mode, mode_flags, \u0026nodes);\nmm/mempolicy.c-3597-\tif (IS_ERR(new))\n" }
35/3	2026/09/03 19:08	llm	kmsan-evaluator	0m Model: gemini-3.7-flash Args: null Results: null Tokens: input: 15626 output: 29 thoughts: 589 Thoughts: Analyzing Memory Policy Creation and Binding Okay, let's dive back into `mempolicy_create` within `mm/mempolicy.c`. I need to solidify my understanding of the common patterns in `do_set_mempolicy` and `mpol_shared_policy_init`. Right, it allocates a temporary scratch space, calls `mpol_new` with the mode, flags, and nodes, grabs the `task_lock` on the current task, then calls `mpol_set_nodemask` to actually apply the node mask to the policy using that scratch space, releases the lock, and then frees the temporary scratch. That's the basic workflow. Now, let's examine `kvm_gmem_bind_node`. Here's the code: ```c static int kvm_gmem_bind_node(struct inode inode, int node) { struct mempolicy pol; nodemask_t nodes; int err; if ((unsigned int)node >= MAX_NUMNODES) return -EINVAL; init_nodemask_of_node(&nodes, node); pol = mempolicy_create(MPOL_BIND, 0, &nodes); if (IS_ERR(pol)) return PTR_ERR(pol); err = mpol_set_shared_policy_range(&GMEM_I(inode)->policy, 0, MAX_LFS_FILESIZE >> PAGE_SHIFT, pol); mpol_put(pol); return err; } ``` The function calls `mempolicy_create` with `MPOL_BIND`, no flags, and a `nodes` mask. This `nodes` variable is initialized on the stack using `init_nodemask_of_node(&nodes, node)`. Need to quickly verify how that initialization happens. Ah, it's just a `nodes_clear` followed by a `node_set`. So, the `nodemask` is fully initialized before being passed. Good. Next, it calls `mpol_set_shared_policy_range`. Let's refresh our memory on that function: ```c int mpol_set_shared_policy_range(struct shared_policy sp, pgoff_t start, pgoff_t end, struct mempolicy pol) { struct sp_node *new = NULL; int err; if (pol) { new = sp_alloc(start, end, pol); if (!new) return -ENOMEM; } err = shared_policy_replace(sp, start, end, new); if (err && new) sp_free(new); return err; } ``` Okay, so `mpol_set_shared_policy_range` allocates an `sp_node` via `sp_alloc` if a policy exists. Then `sp_alloc` is called with start, end, and the policy. It uses `kmem_cache_alloc` to allocate the `sp_node` and then initializes it via `sp_node_init(n, start, end, pol)`. I need to quickly glance at `sp_alloc` to confirm what that looks like.
36/3	2026/09/03 19:08	tool	grepper	0m Args: { "Expression": "sp_alloc", "PathPrefix": "mm/mempolicy.c" } Results: { "Output": "mm/mempolicy.c=3169=static void sp_node_init(struct sp_node node, unsigned long start,\n--\nmm/mempolicy.c-3176-\nmm/mempolicy.c:3177:static struct sp_node sp_alloc(unsigned long start, unsigned long end,\nmm/mempolicy.c-3178-\t\t\t\tstruct mempolicy pol)\n--\nmm/mempolicy.c=3275=void mpol_shared_policy_init(struct shared_policy sp, struct mempolicy mpol)\n--\nmm/mempolicy.c-3301-\t\t/ alloc node covering entire file; adds ref to file's npol /\nmm/mempolicy.c:3302:\t\tsn = sp_alloc(0, MAX_LFS_FILESIZE \u003e\u003e PAGE_SHIFT, npol);\nmm/mempolicy.c-3303-\t\tif (sn)\n--\nmm/mempolicy.c=3332=int mpol_set_shared_policy_range(struct shared_policy sp, pgoff_t start,\n--\nmm/mempolicy.c-3338-\tif (pol) {\nmm/mempolicy.c:3339:\t\tnew = sp_alloc(start, end, pol);\nmm/mempolicy.c-3340-\t\tif (!new)\n" }
37/3	2026/09/03 19:08	llm	kmsan-evaluator	0m Model: gemini-3.7-flash Args: null Results: null Tokens: input: 17320 output: 35 thoughts: 17 Thoughts: Here's a summary of my immediate thought process: Diving into the Node Initialization and Allocation Functions Okay, time to get my hands dirty. I need to refresh my understanding of how our system handles node initialization and allocation. Specifically, I'm thinking about `sp_node_init` and `sp_alloc`. I need to ensure the initialization process is sound and that the memory allocation strategy is still efficient and doesn't have any hidden gotchas. I want to quickly verify that we're still handling edge cases correctly, especially around resource contention or potential memory leaks. It’s also crucial to see if there have been any recent changes in these areas. Let's see what the code has to say.
38/3	2026/09/03 19:08	tool	read-file	0m Args: { "File": "mm/mempolicy.c", "FirstLine": 3168, "LineCount": 25 } Results: { "Contents": "3168:\t\n3169:\tstatic void sp_node_init(struct sp_node node, unsigned long start,\n3170:\t\t\t\tunsigned long end, struct mempolicy pol)\n3171:\t{\n3172:\t\tnode-\u003estart = start;\n3173:\t\tnode-\u003eend = end;\n3174:\t\tnode-\u003epolicy = pol;\n3175:\t}\n3176:\t\n3177:\tstatic struct sp_node sp_alloc(unsigned long start, unsigned long end,\n3178:\t\t\t\t\tstruct mempolicy pol)\n3179:\t{\n3180:\t\tstruct sp_node n;\n3181:\t\tstruct mempolicy newpol;\n3182:\t\n3183:\t\tn = kmem_cache_alloc(sn_cache, GFP_KERNEL);\n3184:\t\tif (!n)\n3185:\t\t\treturn NULL;\n3186:\t\n3187:\t\tnewpol = mpol_dup(pol);\n3188:\t\tif (IS_ERR(newpol)) {\n3189:\t\t\tkmem_cache_free(sn_cache, n);\n3190:\t\t\treturn NULL;\n3191:\t\t}\n3192:\t\tnewpol-\u003eflags \|= MPOL_F_SHARED;\n" }
39/3	2026/09/03 19:08	llm	kmsan-evaluator	0m Model: gemini-3.7-flash Args: null Results: null Tokens: input: 17872 output: 39 thoughts: 290 Thoughts: Analyzing `kvm_gmem_create` for Potential Vulnerabilities Okay, let's dive into this `kvm_gmem_create` function within `virt/kvm/guest_memfd.c`. The core seems to be here: ```c int kvm_gmem_create(struct kvm kvm, struct kvm_create_guest_memfd args) { loff_t size = args->size; u64 flags = args->flags; int node = NUMA_NO_NODE; if (flags & ~kvm_gmem_get_supported_flags(kvm)) return -EINVAL; if (size <= 0 \|\| !PAGE_ALIGNED(size)) return -EINVAL; if (flags & GUEST_MEMFD_FLAG_BIND_NODE) { if (args->pad \|\| args->node >= MAX_NUMNODES) return -EINVAL; node = args->node; } else if (args->node \|\| args->pad) { return -EINVAL; } return __kvm_gmem_create(kvm, size, flags, node); } ``` Now, the important part: I'm scanning this code, looking for potential vulnerabilities, and a red flag just went up. I see checks for `size`, `flags`, and `node`, but... hold on. Where's the validation for `args->reserved`? Is this a new structure or function? Let's assume that there's a reason for this omission, but it's important to look! I need to quickly determine whether `args->reserved` might have been used in any other place. It's really easy to make an error on these new API's and not handle all potential bad values. My next step is to examine the wider context. I need to grep the rest of `guest_memfd.c` and any other relevant files or header files to see if and where the `kvm_create_guest_memfd` structure is declared and how it's used. Maybe the original version of this structure had padding, and this field is meant for alignment, in which case it is expected to be ignored. I want to see how `args` was handled before this particular patch or commit, and if any previous versions included a check for the `reserved` field. That would confirm whether this is a newly introduced oversight, or whether it was always intended to be ignored.
40/3	2026/09/03 19:08	tool	read-file	0m Args: { "File": "virt/kvm/guest_memfd.c", "FirstLine": 590, "LineCount": 50 } Results: { "Contents": " 590:\t\t\terr = kvm_gmem_bind_node(inode, node);\n 591:\t\t\tif (err)\n 592:\t\t\t\tgoto err_inode;\n 593:\t\t}\n 594:\t\n 595:\t\tfile = alloc_file_pseudo(inode, kvm_gmem_mnt, name, O_RDWR, \u0026kvm_gmem_fops);\n 596:\t\tif (IS_ERR(file)) {\n 597:\t\t\terr = PTR_ERR(file);\n 598:\t\t\tgoto err_inode;\n 599:\t\t}\n 600:\t\n 601:\t\tfile-\u003ef_flags \|= O_LARGEFILE;\n 602:\t\tfile-\u003eprivate_data = f;\n 603:\t\n 604:\t\tkvm_get_kvm(kvm);\n 605:\t\tf-\u003ekvm = kvm;\n 606:\t\txa_init(\u0026f-\u003ebindings);\n 607:\t\tlist_add(\u0026f-\u003eentry, \u0026GMEM_I(inode)-\u003egmem_file_list);\n 608:\t\n 609:\t\tfd_install(fd, file);\n 610:\t\treturn fd;\n 611:\t\n 612:\terr_inode:\n 613:\t\tiput(inode);\n 614:\terr_fops:\n 615:\t\tfops_put(\u0026kvm_gmem_fops);\n 616:\terr_gmem:\n 617:\t\tkfree(f);\n 618:\terr_fd:\n 619:\t\tput_unused_fd(fd);\n 620:\t\treturn err;\n 621:\t}\n 622:\t\n 623:\tint kvm_gmem_create(struct kvm kvm, struct kvm_create_guest_memfd args)\n 624:\t{\n 625:\t\tloff_t size = args-\u003esize;\n 626:\t\tu64 flags = args-\u003eflags;\n 627:\t\tint node = NUMA_NO_NODE;\n 628:\t\n 629:\t\tif (flags \u0026 ~kvm_gmem_get_supported_flags(kvm))\n 630:\t\t\treturn -EINVAL;\n 631:\t\n 632:\t\tif (size \u003c= 0 \|\| !PAGE_ALIGNED(size))\n 633:\t\t\treturn -EINVAL;\n 634:\t\n 635:\t\tif (flags \u0026 GUEST_MEMFD_FLAG_BIND_NODE) {\n 636:\t\t\tif (args-\u003epad \|\| args-\u003enode \u003e= MAX_NUMNODES)\n 637:\t\t\t\treturn -EINVAL;\n 638:\t\t\tnode = args-\u003enode;\n 639:\t\t} else if (args-\u003enode \|\| args-\u003epad) {\n" }
41/3	2026/09/03 19:08	llm	kmsan-evaluator	0m Model: gemini-3.7-flash Args: null Results: null Tokens: input: 19497 output: 335 thoughts: 850 Thoughts: KMSAN Analysis of Guest Memfd Patch Okay, let's break this down. First, the `args` passed into `kvm_gmem_create` after `copy_from_user` in `kvm_vm_ioctl` is the entry point, and then the critical thing is that nothing is copied back to userspace. No uninitialized memory is read or leaked. Good. I'm also confirming that no kernel structures sent to userspace are modified. Now, let's meticulously check for branches dependent on uninitialized variables, which is where KMSAN usually bites. I see `nodes` in `kvm_gmem_bind_node` gets initialized with `init_nodemask_of_node`. `scratch` in `mempolicy_create` is covered by `NODEMASK_SCRATCH`. `new` in `mpol_set_shared_policy_range` is initialized to NULL or `sp_alloc`. The `guest_memfd` argument, read from userspace via `copy_from_user`, is of particular note, but seems safe. And, finally, `node` in `kvm_gmem_create` is initialized, too. All variables are properly initialized. No new data is exposed to userspace – no information leaks. That's a huge win. Let's run through the KMSAN criteria methodically, to make sure I haven't missed anything. 1. Kernel structures sent to userspace: No `copy_to_user` here, the `KVM_CREATE_GUEST_MEMFD` ioctl simply returns an FD. This is clean. 2. Conditional logic on uninitialized variables: Nope, all stack variables like `nodes`, `scratch`, `node` are properly initialized. 3. Allocation of complex data structures: `mempolicy_create` builds a validated `struct mempolicy` using standard `mpol_new` / `mpol_set_nodemask`. `sp_alloc` covers `sp_node` initialization. Fine. 4. Bounds checks exposing uninitialized bytes: Not relevant here. Therefore, no uninitialized memory risks are introduced by this patch. Any potential memory safety issues that do arise (use-after-free, refcount problems in mempolicy or gmem) would be handled by KASAN – and KASAN is already enabled. Thus, `NeedsKMSAN` should be set to `false`. So, the KMSAN reasoning is: KMSAN detects reads of uninitialized memory and info leaks. This patch adds `GUEST_MEMFD_FLAG_BIND_NODE` and related helpers in `mm/mempolicy.c`. The ioctl `KVM_CREATE_GUEST_MEMFD` copies arguments from userspace but doesn't copy kernel data back. All variables and structures are initialized. Any memory management issues are KASAN's domain. No KMSAN needed. Okay, time to invoke `set-results`.
42/3	2026/09/03 19:09	tool	set-results	0m Args: { "KMSANReasoning": "The patch introduces support for the `GUEST_MEMFD_FLAG_BIND_NODE` flag in KVM's guest_memfd subsystem along with helper functions `mempolicy_create()` and `mpol_set_shared_policy_range()` in `mm/mempolicy.c`.\n\nKMSAN vs KASAN applicability:\n- KMSAN detects uninitialized memory reads (on stack, heap, or page allocations) and info-leaks to userspace.\n- In this patch, the `KVM_CREATE_GUEST_MEMFD` ioctl reads user arguments via `copy_from_user` and returns a file descriptor integer; no kernel structures, padding, or buffers are copied back to user space.\n- All newly introduced or modified stack and heap variables (e.g., `nodemask_t nodes` initialized via `init_nodemask_of_node()`, `scratch` initialized via `NODEMASK_SCRATCH()`, and `struct sp_node`/`struct mempolicy` allocated and initialized through standard mm helpers) are fully initialized before use.\n- There are no branching conditions on uninitialized memory or altered data buffer length calculations that could expose uninitialized bytes.\n- Any potential issues (such as NUMA policy reference counting, lifecycle issues, or allocation failures) fall under the scope of KASAN, LOCKDEP, and standard kernel debugging facilities.\n\nTherefore, a dedicated KMSAN fuzzing session is not warranted.", "NeedsKMSAN": false } Results: { "KMSANReasoning": "The patch introduces support for the `GUEST_MEMFD_FLAG_BIND_NODE` flag in KVM's guest_memfd subsystem along with helper functions `mempolicy_create()` and `mpol_set_shared_policy_range()` in `mm/mempolicy.c`.\n\nKMSAN vs KASAN applicability:\n- KMSAN detects uninitialized memory reads (on stack, heap, or page allocations) and info-leaks to userspace.\n- In this patch, the `KVM_CREATE_GUEST_MEMFD` ioctl reads user arguments via `copy_from_user` and returns a file descriptor integer; no kernel structures, padding, or buffers are copied back to user space.\n- All newly introduced or modified stack and heap variables (e.g., `nodemask_t nodes` initialized via `init_nodemask_of_node()`, `scratch` initialized via `NODEMASK_SCRATCH()`, and `struct sp_node`/`struct mempolicy` allocated and initialized through standard mm helpers) are fully initialized before use.\n- There are no branching conditions on uninitialized memory or altered data buffer length calculations that could expose uninitialized bytes.\n- Any potential issues (such as NUMA policy reference counting, lifecycle issues, or allocation failures) fall under the scope of KASAN, LOCKDEP, and standard kernel debugging facilities.\n\nTherefore, a dedicated KMSAN fuzzing session is not warranted.", "NeedsKMSAN": false }

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