AI Trajectory

null

{
  "EnableConfigs": [
    "PTDUMP_DEBUGFS",
    "DEBUG_WX",
    "CPA_DEBUG"
  ],
  "FocusSymbols": [
    "vmap_try_huge_pmd",
    "vmap_try_huge_pud",
    "vmap_try_huge_p4d",
    "cpa_collapse_large_pages",
    "__change_page_attr_set_clr",
    "ptdump_walk_pgd",
    "walk_page_range_debug",
    "pmd_free_pte_page",
    "pud_free_pmd_page"
  ],
  "Reasoning": "The patch modifies page table dumping (ptdump), vmalloc huge page setup, and x86 Change Page Attribute (CPA) code to use `init_mm.mmap_lock` for synchronization. This replaces a static key approach in arm64 and adds locking in x86 CPA and vmalloc. This is a functional change to core memory management and should be fuzzed to ensure no deadlocks or use-after-free issues occur during concurrent page table walks and modifications.",
  "WorthFuzzing": true
}

null

{
  "PatchDiff": "commit ce88ec516aa3af872d15c45501e55b382bc19527\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate:   Fri Jul 17 22:23:04 2026 +0000\n\n    syz-cluster: applied patch under review\n\ndiff --git a/arch/arm64/include/asm/ptdump.h b/arch/arm64/include/asm/ptdump.h\nindex 5b374a6ab34a4e..50a195eda8ed22 100644\n--- a/arch/arm64/include/asm/ptdump.h\n+++ b/arch/arm64/include/asm/ptdump.h\n@@ -7,8 +7,6 @@\n \n #include \u003clinux/ptdump.h\u003e\n \n-DECLARE_STATIC_KEY_FALSE(arm64_ptdump_lock_key);\n-\n #ifdef CONFIG_PTDUMP\n \n #include \u003clinux/mm_types.h\u003e\ndiff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c\nindex a25d8beacc8310..bd52fca6e8720b 100644\n--- a/arch/arm64/mm/mmu.c\n+++ b/arch/arm64/mm/mmu.c\n@@ -49,8 +49,6 @@\n #define NO_CONT_MAPPINGS\tBIT(1)\n #define NO_EXEC_MAPPINGS\tBIT(2)\t/* assumes FEAT_HPDS is not used */\n \n-DEFINE_STATIC_KEY_FALSE(arm64_ptdump_lock_key);\n-\n u64 kimage_voffset __ro_after_init;\n EXPORT_SYMBOL(kimage_voffset);\n \n@@ -1864,8 +1862,7 @@ int pmd_clear_huge(pmd_t *pmdp)\n \treturn 1;\n }\n \n-static int __pmd_free_pte_page(pmd_t *pmdp, unsigned long addr,\n-\t\t\t       bool acquire_mmap_lock)\n+int pmd_free_pte_page(pmd_t *pmdp, unsigned long addr)\n {\n \tpte_t *table;\n \tpmd_t pmd;\n@@ -1877,25 +1874,13 @@ static int __pmd_free_pte_page(pmd_t *pmdp, unsigned long addr,\n \t\treturn 1;\n \t}\n \n-\t/* See comment in pud_free_pmd_page for static key logic */\n \ttable = pte_offset_kernel(pmdp, addr);\n \tpmd_clear(pmdp);\n \t__flush_tlb_kernel_pgtable(addr);\n-\tif (static_branch_unlikely(\u0026arm64_ptdump_lock_key) \u0026\u0026 acquire_mmap_lock) {\n-\t\tmmap_read_lock(\u0026init_mm);\n-\t\tmmap_read_unlock(\u0026init_mm);\n-\t}\n-\n \tpte_free_kernel(NULL, table);\n \treturn 1;\n }\n \n-int pmd_free_pte_page(pmd_t *pmdp, unsigned long addr)\n-{\n-\t/* If ptdump is walking the pagetables, acquire init_mm.mmap_lock */\n-\treturn __pmd_free_pte_page(pmdp, addr, /* acquire_mmap_lock = */ true);\n-}\n-\n int pud_free_pmd_page(pud_t *pudp, unsigned long addr)\n {\n \tpmd_t *table;\n@@ -1911,36 +1896,16 @@ int pud_free_pmd_page(pud_t *pudp, unsigned long addr)\n \t}\n \n \ttable = pmd_offset(pudp, addr);\n-\n-\t/*\n-\t * Our objective is to prevent ptdump from reading a PMD table which has\n-\t * been freed. In this race, if pud_free_pmd_page observes the key on\n-\t * (which got flipped by ptdump) then the mmap lock sequence here will,\n-\t * as a result of the mmap write lock/unlock sequence in ptdump, give\n-\t * us the correct synchronization. If not, this means that ptdump has\n-\t * yet not started walking the pagetables - the sequence of barriers\n-\t * issued by __flush_tlb_kernel_pgtable() guarantees that ptdump will\n-\t * observe an empty PUD.\n-\t */\n-\tpud_clear(pudp);\n-\t__flush_tlb_kernel_pgtable(addr);\n-\tif (static_branch_unlikely(\u0026arm64_ptdump_lock_key)) {\n-\t\tmmap_read_lock(\u0026init_mm);\n-\t\tmmap_read_unlock(\u0026init_mm);\n-\t}\n-\n \tpmdp = table;\n \tnext = addr;\n \tend = addr + PUD_SIZE;\n \tdo {\n \t\tif (pmd_present(pmdp_get(pmdp)))\n-\t\t\t/*\n-\t\t\t * PMD has been isolated, so ptdump won't see it. No\n-\t\t\t * need to acquire init_mm.mmap_lock.\n-\t\t\t */\n-\t\t\t__pmd_free_pte_page(pmdp, next, /* acquire_mmap_lock = */ false);\n+\t\t\tpmd_free_pte_page(pmdp, next);\n \t} while (pmdp++, next += PMD_SIZE, next != end);\n \n+\tpud_clear(pudp);\n+\t__flush_tlb_kernel_pgtable(addr);\n \tpmd_free(NULL, table);\n \treturn 1;\n }\ndiff --git a/arch/arm64/mm/ptdump.c b/arch/arm64/mm/ptdump.c\nindex 1c20144700d7d7..5a76c59b5ada55 100644\n--- a/arch/arm64/mm/ptdump.c\n+++ b/arch/arm64/mm/ptdump.c\n@@ -283,13 +283,6 @@ void note_page_flush(struct ptdump_state *pt_st)\n \tnote_page(pt_st, 0, -1, pte_val(pte_zero));\n }\n \n-static void arm64_ptdump_walk_pgd(struct ptdump_state *st, struct mm_struct *mm)\n-{\n-\tstatic_branch_inc(\u0026arm64_ptdump_lock_key);\n-\tptdump_walk_pgd(st, mm, NULL);\n-\tstatic_branch_dec(\u0026arm64_ptdump_lock_key);\n-}\n-\n void ptdump_walk(struct seq_file *s, struct ptdump_info *info)\n {\n \tunsigned long end = ~0UL;\n@@ -318,7 +311,7 @@ void ptdump_walk(struct seq_file *s, struct ptdump_info *info)\n \t\t}\n \t};\n \n-\tarm64_ptdump_walk_pgd(\u0026st.ptdump, info-\u003emm);\n+\tptdump_walk_pgd(\u0026st.ptdump, info-\u003emm, NULL);\n }\n \n static void __init ptdump_initialize(void)\n@@ -360,7 +353,7 @@ bool ptdump_check_wx(void)\n \t\t}\n \t};\n \n-\tarm64_ptdump_walk_pgd(\u0026st.ptdump, \u0026init_mm);\n+\tptdump_walk_pgd(\u0026st.ptdump, \u0026init_mm, NULL);\n \n \tif (st.wx_pages || st.uxn_pages) {\n \t\tpr_warn(\"Checked W+X mappings: FAILED, %lu W+X pages found, %lu non-UXN pages found\\n\",\ndiff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c\nindex d023a40a1e0345..301fb9e77d91ba 100644\n--- a/arch/x86/mm/pat/set_memory.c\n+++ b/arch/x86/mm/pat/set_memory.c\n@@ -22,6 +22,7 @@\n #include \u003clinux/cc_platform.h\u003e\n #include \u003clinux/set_memory.h\u003e\n #include \u003clinux/memregion.h\u003e\n+#include \u003clinux/cleanup.h\u003e\n \n #include \u003casm/e820/api.h\u003e\n #include \u003casm/processor.h\u003e\n@@ -410,7 +411,7 @@ static void __cpa_flush_tlb(void *data)\n \n static int collapse_large_pages(unsigned long addr, struct list_head *pgtables);\n \n-static void cpa_collapse_large_pages(struct cpa_data *cpa)\n+static void __cpa_collapse_large_pages(struct cpa_data *cpa)\n {\n \tunsigned long start, addr, end;\n \tstruct ptdesc *ptdesc, *tmp;\n@@ -442,6 +443,18 @@ static void cpa_collapse_large_pages(struct cpa_data *cpa)\n \t}\n }\n \n+static void cpa_collapse_large_pages(struct cpa_data *cpa)\n+{\n+\t/*\n+\t * Take the mmap write lock on init_mm to:\n+\t * - Avoid a use-after-free if raced by ptdump (which takes its own\n+\t *   write lock on init_mm).\n+\t * - Serialise concurrent CPA walkers.\n+\t */\n+\tscoped_guard(mmap_write_lock, \u0026init_mm)\n+\t\t__cpa_collapse_large_pages(cpa);\n+}\n+\n static void cpa_flush(struct cpa_data *cpa, int cache)\n {\n \tunsigned int i;\n@@ -2109,7 +2122,9 @@ static int change_page_attr_set_clr(unsigned long *addr, int numpages,\n \tcpa.curpage = 0;\n \tcpa.force_split = force_split;\n \n-\tret = __change_page_attr_set_clr(\u0026cpa, 1);\n+\t/* Avoid race with concurrent CPA collapse. */\n+\tscoped_guard(mmap_read_lock, \u0026init_mm)\n+\t\tret = __change_page_attr_set_clr(\u0026cpa, 1);\n \n \t/*\n \t * Check whether we really changed something:\ndiff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h\nindex 04b8f61ece5d8e..047f5f5e2c3475 100644\n--- a/include/linux/mmap_lock.h\n+++ b/include/linux/mmap_lock.h\n@@ -621,6 +621,9 @@ static inline void mmap_read_unlock(struct mm_struct *mm)\n \n DEFINE_GUARD(mmap_read_lock, struct mm_struct *,\n \t     mmap_read_lock(_T), mmap_read_unlock(_T))\n+DEFINE_GUARD(mmap_write_lock, struct mm_struct *,\n+\t     mmap_write_lock(_T), mmap_write_unlock(_T))\n+DEFINE_GUARD_COND(mmap_read_lock, _try, mmap_read_trylock(_T))\n \n static inline void mmap_read_unlock_non_owner(struct mm_struct *mm)\n {\ndiff --git a/mm/pagewalk.c b/mm/pagewalk.c\nindex 3ae2586ff45b44..5d87c632a25507 100644\n--- a/mm/pagewalk.c\n+++ b/mm/pagewalk.c\n@@ -678,6 +678,8 @@ int walk_kernel_page_table_range_lockless(unsigned long start, unsigned long end\n  * will also not lock the PTEs for the pte_entry() callback.\n  *\n  * This is for debugging purposes ONLY.\n+ *\n+ * The mmap write lock must be held.\n  */\n int walk_page_range_debug(struct mm_struct *mm, unsigned long start,\n \t\t\t  unsigned long end, const struct mm_walk_ops *ops,\n@@ -691,24 +693,28 @@ int walk_page_range_debug(struct mm_struct *mm, unsigned long start,\n \t\t.no_vma\t\t= true\n \t};\n \n-\t/* For convenience, we allow traversal of kernel mappings. */\n-\tif (mm == \u0026init_mm)\n-\t\treturn walk_kernel_page_table_range(start, end, ops,\n-\t\t\t\t\t\t    pgd, private);\n-\tif (start \u003e= end || !walk.mm)\n-\t\treturn -EINVAL;\n-\tif (!check_ops_safe(ops))\n-\t\treturn -EINVAL;\n-\n \t/*\n-\t * The mmap lock protects the page walker from changes to the page\n-\t * tables during the walk.  However a read lock is insufficient to\n-\t * protect those areas which don't have a VMA as munmap() detaches\n-\t * the VMAs before downgrading to a read lock and actually tearing\n-\t * down PTEs/page tables. In which case, the mmap write lock should\n-\t * be held.\n+\t * When walking userland page tables, an mmap write lock must be held to\n+\t * account for munmap() downgrading to an mmap read lock when tearing\n+\t * down page tables.\n+\t *\n+\t * When walking kernel page tables, an mmap write lock must also be held\n+\t * to account for page table freeing on vmap huge page mapping.\n \t */\n \tmmap_assert_write_locked(mm);\n+\t/*\n+\t * x86, arm64 ptdump allow walks of efi mm's and x86 ptdump allows walks\n+\t * of arbitrary mm's.\n+\t *\n+\t * However, they both must also hold the init_mm lock to account for\n+\t * concurrent kernel page table freeing.\n+\t */\n+\tmmap_assert_write_locked(\u0026init_mm);\n+\n+\tif (start \u003e= end)\n+\t\treturn -EINVAL;\n+\tif (!check_ops_safe(ops))\n+\t\treturn -EINVAL;\n \n \treturn walk_pgd_range(start, end, \u0026walk);\n }\ndiff --git a/mm/ptdump.c b/mm/ptdump.c\nindex 973020000096cf..5851096e6f656c 100644\n--- a/mm/ptdump.c\n+++ b/mm/ptdump.c\n@@ -178,11 +178,18 @@ void ptdump_walk_pgd(struct ptdump_state *st, struct mm_struct *mm, pgd_t *pgd)\n \n \tget_online_mems();\n \tmmap_write_lock(mm);\n+\t/* To stabilise kernel page tables we must hold the init_mm lock too. */\n+\tif (mm != \u0026init_mm)\n+\t\tmmap_write_lock_nested(\u0026init_mm, SINGLE_DEPTH_NESTING);\n+\n \twhile (range-\u003estart != range-\u003eend) {\n \t\twalk_page_range_debug(mm, range-\u003estart, range-\u003eend,\n \t\t\t\t      \u0026ptdump_ops, pgd, st);\n \t\trange++;\n \t}\n+\n+\tif (mm != \u0026init_mm)\n+\t\tmmap_write_unlock(\u0026init_mm);\n \tmmap_write_unlock(mm);\n \tput_online_mems();\n \ndiff --git a/mm/vmalloc.c b/mm/vmalloc.c\nindex 1afca3568b9b65..f4fa227a8d7f04 100644\n--- a/mm/vmalloc.c\n+++ b/mm/vmalloc.c\n@@ -43,6 +43,7 @@\n #include \u003casm/tlbflush.h\u003e\n #include \u003casm/shmparam.h\u003e\n #include \u003clinux/page_owner.h\u003e\n+#include \u003clinux/cleanup.h\u003e\n \n #define CREATE_TRACE_POINTS\n #include \u003ctrace/events/vmalloc.h\u003e\n@@ -158,10 +159,21 @@ static int vmap_try_huge_pmd(pmd_t *pmd, unsigned long addr, unsigned long end,\n \tif (!IS_ALIGNED(phys_addr, PMD_SIZE))\n \t\treturn 0;\n \n-\tif (pmd_present(*pmd) \u0026\u0026 !pmd_free_pte_page(pmd, addr))\n-\t\treturn 0;\n+\tif (!pmd_present(*pmd))\n+\t\treturn pmd_set_huge(pmd, phys_addr, prot);\n \n-\treturn pmd_set_huge(pmd, phys_addr, prot);\n+\t/*\n+\t * Acquire the mmap read lock to exclude ptdump, which walks\n+\t * kernel page tables it does not own under the mmap write lock.\n+\t *\n+\t * Concurrent read lock holders are safe: each exclusively owns\n+\t * the range it operates on and cannot reach this page table.\n+\t */\n+\tscoped_cond_guard(mmap_read_lock_try, return 0, \u0026init_mm) {\n+\t\tif (!pmd_free_pte_page(pmd, addr))\n+\t\t\treturn 0;\n+\t\treturn pmd_set_huge(pmd, phys_addr, prot);\n+\t}\n }\n \n static int vmap_pmd_range(pud_t *pud, unsigned long addr, unsigned long end,\n@@ -210,10 +222,15 @@ static int vmap_try_huge_pud(pud_t *pud, unsigned long addr, unsigned long end,\n \tif (!IS_ALIGNED(phys_addr, PUD_SIZE))\n \t\treturn 0;\n \n-\tif (pud_present(*pud) \u0026\u0026 !pud_free_pmd_page(pud, addr))\n-\t\treturn 0;\n+\tif (!pud_present(*pud))\n+\t\treturn pud_set_huge(pud, phys_addr, prot);\n \n-\treturn pud_set_huge(pud, phys_addr, prot);\n+\t/* See comment in vmap_try_huge_pmd(). */\n+\tscoped_cond_guard(mmap_read_lock_try, return 0, \u0026init_mm) {\n+\t\tif (!pud_free_pmd_page(pud, addr))\n+\t\t\treturn 0;\n+\t\treturn pud_set_huge(pud, phys_addr, prot);\n+\t}\n }\n \n static int vmap_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end,\n@@ -262,10 +279,15 @@ static int vmap_try_huge_p4d(p4d_t *p4d, unsigned long addr, unsigned long end,\n \tif (!IS_ALIGNED(phys_addr, P4D_SIZE))\n \t\treturn 0;\n \n-\tif (p4d_present(*p4d) \u0026\u0026 !p4d_free_pud_page(p4d, addr))\n-\t\treturn 0;\n+\tif (!p4d_present(*p4d))\n+\t\treturn p4d_set_huge(p4d, phys_addr, prot);\n \n-\treturn p4d_set_huge(p4d, phys_addr, prot);\n+\t/* See comment in vmap_try_huge_pmd(). */\n+\tscoped_cond_guard(mmap_read_lock_try, return 0, \u0026init_mm) {\n+\t\tif (!p4d_free_pud_page(p4d, addr))\n+\t\t\treturn 0;\n+\t\treturn p4d_set_huge(p4d, phys_addr, prot);\n+\t}\n }\n \n static int vmap_p4d_range(pgd_t *pgd, unsigned long addr, unsigned long end,\n"
}

gemini-3.1-pro-preview

null

{
  "EnableConfigs": [
    "PTDUMP_DEBUGFS",
    "DEBUG_WX",
    "CPA_DEBUG"
  ],
  "FocusSymbols": [
    "vmap_try_huge_pmd",
    "vmap_try_huge_pud",
    "vmap_try_huge_p4d",
    "cpa_collapse_large_pages",
    "__change_page_attr_set_clr",
    "ptdump_walk_pgd",
    "walk_page_range_debug",
    "pmd_free_pte_page",
    "pud_free_pmd_page"
  ],
  "Reasoning": "The patch modifies page table dumping (ptdump), vmalloc huge page setup, and x86 Change Page Attribute (CPA) code to use `init_mm.mmap_lock` for synchronization. This replaces a static key approach in arm64 and adds locking in x86 CPA and vmalloc. This is a functional change to core memory management and should be fuzzed to ensure no deadlocks or use-after-free issues occur during concurrent page table walks and modifications.",
  "WorthFuzzing": true
}

You are an expert Linux kernel maintainer.
Your job is to review a provided patch series and determine
if it makes functional changes to the kernel that should be fuzzed.

IMPORTANT: The changes have ALREADY been applied and committed as the HEAD commit in
your workspace. Do NOT rely on your internal knowledge of the kernel. You must actively
use your code access tools to examine the actual source code and confirm any assumptions.

Return WorthFuzzing=false if the patch only contains:
- Modifications to Documentation/, Kconfig files, or code comments.
- Purely decorative changes, such as logging (e.g., pr_err, printk) or tracepoints.
- Changes to numeric constants or macros that do not functionally alter execution flow.
- Code paths that are impossible to reach in virtualized environments like GCE or QEMU,
even when utilizing software-emulated hardware (e.g., usb gadget, mac80211_hwsim).

If it modifies reachable core kernel logic, drivers, or architectures, use your code search
tools to verify the code can be executed, then return WorthFuzzing=true.

When returning WorthFuzzing=true, you MUST ALSO:
1. Extract any specific kernel functions that should be heavily fuzzed into FocusSymbols.
   Avoid listing generic hot-path functions to prevent skewed test distributions.
2. Identify any specific CONFIG_ options required to properly test this new/modified feature.
   Go and look into the Kconfig files and check for ifdefs around the code, do not make assumptions.
   Do not list too generic configs (we already have them enabled). Only list those that
   specifically cover the modified code. List them in the EnableConfigs output array,
   and DO NOT add a '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.

For your convenience, here is the diff of the changes:
commit ce88ec516aa3af872d15c45501e55b382bc19527
Author: syz-cluster <triage@syzkaller.com>
Date:   Fri Jul 17 22:23:04 2026 +0000

    syz-cluster: applied patch under review

diff --git a/arch/arm64/include/asm/ptdump.h b/arch/arm64/include/asm/ptdump.h
index 5b374a6ab34a4e..50a195eda8ed22 100644
--- a/arch/arm64/include/asm/ptdump.h
+++ b/arch/arm64/include/asm/ptdump.h
@@ -7,8 +7,6 @@
 
 #include <linux/ptdump.h>
 
-DECLARE_STATIC_KEY_FALSE(arm64_ptdump_lock_key);
-
 #ifdef CONFIG_PTDUMP
 
 #include <linux/mm_types.h>
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index a25d8beacc8310..bd52fca6e8720b 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -49,8 +49,6 @@
 #define NO_CONT_MAPPINGS	BIT(1)
 #define NO_EXEC_MAPPINGS	BIT(2)	/* assumes FEAT_HPDS is not used */
 
-DEFINE_STATIC_KEY_FALSE(arm64_ptdump_lock_key);
-
 u64 kimage_voffset __ro_after_init;
 EXPORT_SYMBOL(kimage_voffset);
 
@@ -1864,8 +1862,7 @@ int pmd_clear_huge(pmd_t *pmdp)
 	return 1;
 }
 
-static int __pmd_free_pte_page(pmd_t *pmdp, unsigned long addr,
-			       bool acquire_mmap_lock)
+int pmd_free_pte_page(pmd_t *pmdp, unsigned long addr)
 {
 	pte_t *table;
 	pmd_t pmd;
@@ -1877,25 +1874,13 @@ static int __pmd_free_pte_page(pmd_t *pmdp, unsigned long addr,
 		return 1;
 	}
 
-	/* See comment in pud_free_pmd_page for static key logic */
 	table = pte_offset_kernel(pmdp, addr);
 	pmd_clear(pmdp);
 	__flush_tlb_kernel_pgtable(addr);
-	if (static_branch_unlikely(&arm64_ptdump_lock_key) && acquire_mmap_lock) {
-		mmap_read_lock(&init_mm);
-		mmap_read_unlock(&init_mm);
-	}
-
 	pte_free_kernel(NULL, table);
 	return 1;
 }
 
-int pmd_free_pte_page(pmd_t *pmdp, unsigned long addr)
-{
-	/* If ptdump is walking the pagetables, acquire init_mm.mmap_lock */
-	return __pmd_free_pte_page(pmdp, addr, /* acquire_mmap_lock = */ true);
-}
-
 int pud_free_pmd_page(pud_t *pudp, unsigned long addr)
 {
 	pmd_t *table;
@@ -1911,36 +1896,16 @@ int pud_free_pmd_page(pud_t *pudp, unsigned long addr)
 	}
 
 	table = pmd_offset(pudp, addr);
-
-	/*
-	 * Our objective is to prevent ptdump from reading a PMD table which has
-	 * been freed. In this race, if pud_free_pmd_page observes the key on
-	 * (which got flipped by ptdump) then the mmap lock sequence here will,
-	 * as a result of the mmap write lock/unlock sequence in ptdump, give
-	 * us the correct synchronization. If not, this means that ptdump has
-	 * yet not started walking the pagetables - the sequence of barriers
-	 * issued by __flush_tlb_kernel_pgtable() guarantees that ptdump will
-	 * observe an empty PUD.
-	 */
-	pud_clear(pudp);
-	__flush_tlb_kernel_pgtable(addr);
-	if (static_branch_unlikely(&arm64_ptdump_lock_key)) {
-		mmap_read_lock(&init_mm);
-		mmap_read_unlock(&init_mm);
-	}
-
 	pmdp = table;
 	next = addr;
 	end = addr + PUD_SIZE;
 	do {
 		if (pmd_present(pmdp_get(pmdp)))
-			/*
-			 * PMD has been isolated, so ptdump won't see it. No
-			 * need to acquire init_mm.mmap_lock.
-			 */
-			__pmd_free_pte_page(pmdp, next, /* acquire_mmap_lock = */ false);
+			pmd_free_pte_page(pmdp, next);
 	} while (pmdp++, next += PMD_SIZE, next != end);
 
+	pud_clear(pudp);
+	__flush_tlb_kernel_pgtable(addr);
 	pmd_free(NULL, table);
 	return 1;
 }
diff --git a/arch/arm64/mm/ptdump.c b/arch/arm64/mm/ptdump.c
index 1c20144700d7d7..5a76c59b5ada55 100644
--- a/arch/arm64/mm/ptdump.c
+++ b/arch/arm64/mm/ptdump.c
@@ -283,13 +283,6 @@ void note_page_flush(struct ptdump_state *pt_st)
 	note_page(pt_st, 0, -1, pte_val(pte_zero));
 }
 
-static void arm64_ptdump_walk_pgd(struct ptdump_state *st, struct mm_struct *mm)
-{
-	static_branch_inc(&arm64_ptdump_lock_key);
-	ptdump_walk_pgd(st, mm, NULL);
-	static_branch_dec(&arm64_ptdump_lock_key);
-}
-
 void ptdump_walk(struct seq_file *s, struct ptdump_info *info)
 {
 	unsigned long end = ~0UL;
@@ -318,7 +311,7 @@ void ptdump_walk(struct seq_file *s, struct ptdump_info *info)
 		}
 	};
 
-	arm64_ptdump_walk_pgd(&st.ptdump, info->mm);
+	ptdump_walk_pgd(&st.ptdump, info->mm, NULL);
 }
 
 static void __init ptdump_initialize(void)
@@ -360,7 +353,7 @@ bool ptdump_check_wx(void)
 		}
 	};
 
-	arm64_ptdump_walk_pgd(&st.ptdump, &init_mm);
+	ptdump_walk_pgd(&st.ptdump, &init_mm, NULL);
 
 	if (st.wx_pages || st.uxn_pages) {
 		pr_warn("Checked W+X mappings: FAILED, %lu W+X pages found, %lu non-UXN pages found\n",
diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index d023a40a1e0345..301fb9e77d91ba 100644
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -22,6 +22,7 @@
 #include <linux/cc_platform.h>
 #include <linux/set_memory.h>
 #include <linux/memregion.h>
+#include <linux/cleanup.h>
 
 #include <asm/e820/api.h>
 #include <asm/processor.h>
@@ -410,7 +411,7 @@ static void __cpa_flush_tlb(void *data)
 
 static int collapse_large_pages(unsigned long addr, struct list_head *pgtables);
 
-static void cpa_collapse_large_pages(struct cpa_data *cpa)
+static void __cpa_collapse_large_pages(struct cpa_data *cpa)
 {
 	unsigned long start, addr, end;
 	struct ptdesc *ptdesc, *tmp;
@@ -442,6 +443,18 @@ static void cpa_collapse_large_pages(struct cpa_data *cpa)
 	}
 }
 
+static void cpa_collapse_large_pages(struct cpa_data *cpa)
+{
+	/*
+	 * Take the mmap write lock on init_mm to:
+	 * - Avoid a use-after-free if raced by ptdump (which takes its own
+	 *   write lock on init_mm).
+	 * - Serialise concurrent CPA walkers.
+	 */
+	scoped_guard(mmap_write_lock, &init_mm)
+		__cpa_collapse_large_pages(cpa);
+}
+
 static void cpa_flush(struct cpa_data *cpa, int cache)
 {
 	unsigned int i;
@@ -2109,7 +2122,9 @@ static int change_page_attr_set_clr(unsigned long *addr, int numpages,
 	cpa.curpage = 0;
 	cpa.force_split = force_split;
 
-	ret = __change_page_attr_set_clr(&cpa, 1);
+	/* Avoid race with concurrent CPA collapse. */
+	scoped_guard(mmap_read_lock, &init_mm)
+		ret = __change_page_attr_set_clr(&cpa, 1);
 
 	/*
 	 * Check whether we really changed something:
diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h
index 04b8f61ece5d8e..047f5f5e2c3475 100644
--- a/include/linux/mmap_lock.h
+++ b/include/linux/mmap_lock.h
@@ -621,6 +621,9 @@ static inline void mmap_read_unlock(struct mm_struct *mm)
 
 DEFINE_GUARD(mmap_read_lock, struct mm_struct *,
 	     mmap_read_lock(_T), mmap_read_unlock(_T))
+DEFINE_GUARD(mmap_write_lock, struct mm_struct *,
+	     mmap_write_lock(_T), mmap_write_unlock(_T))
+DEFINE_GUARD_COND(mmap_read_lock, _try, mmap_read_trylock(_T))
 
 static inline void mmap_read_unlock_non_owner(struct mm_struct *mm)
 {
diff --git a/mm/pagewalk.c b/mm/pagewalk.c
index 3ae2586ff45b44..5d87c632a25507 100644
--- a/mm/pagewalk.c
+++ b/mm/pagewalk.c
@@ -678,6 +678,8 @@ int walk_kernel_page_table_range_lockless(unsigned long start, unsigned long end
  * will also not lock the PTEs for the pte_entry() callback.
  *
  * This is for debugging purposes ONLY.
+ *
+ * The mmap write lock must be held.
  */
 int walk_page_range_debug(struct mm_struct *mm, unsigned long start,
 			  unsigned long end, const struct mm_walk_ops *ops,
@@ -691,24 +693,28 @@ int walk_page_range_debug(struct mm_struct *mm, unsigned long start,
 		.no_vma		= true
 	};
 
-	/* For convenience, we allow traversal of kernel mappings. */
-	if (mm == &init_mm)
-		return walk_kernel_page_table_range(start, end, ops,
-						    pgd, private);
-	if (start >= end || !walk.mm)
-		return -EINVAL;
-	if (!check_ops_safe(ops))
-		return -EINVAL;
-
 	/*
-	 * The mmap lock protects the page walker from changes to the page
-	 * tables during the walk.  However a read lock is insufficient to
-	 * protect those areas which don't have a VMA as munmap() detaches
-	 * the VMAs before downgrading to a read lock and actually tearing
-	 * down PTEs/page tables. In which case, the mmap write lock should
-	 * be held.
+	 * When walking userland page tables, an mmap write lock must be held to
+	 * account for munmap() downgrading to an mmap read lock when tearing
+	 * down page tables.
+	 *
+	 * When walking kernel page tables, an mmap write lock must also be held
+	 * to account for page table freeing on vmap huge page mapping.
 	 */
 	mmap_assert_write_locked(mm);
+	/*
+	 * x86, arm64 ptdump allow walks of efi mm's and x86 ptdump allows walks
+	 * of arbitrary mm's.
+	 *
+	 * However, they both must also hold the init_mm lock to account for
+	 * concurrent kernel page table freeing.
+	 */
+	mmap_assert_write_locked(&init_mm);
+
+	if (start >= end)
+		return -EINVAL;
+	if (!check_ops_safe(ops))
+		return -EINVAL;
 
 	return walk_pgd_range(start, end, &walk);
 }
diff --git a/mm/ptdump.c b/mm/ptdump.c
index 973020000096cf..5851096e6f656c 100644
--- a/mm/ptdump.c
+++ b/mm/ptdump.c
@@ -178,11 +178,18 @@ void ptdump_walk_pgd(struct ptdump_state *st, struct mm_struct *mm, pgd_t *pgd)
 
 	get_online_mems();
 	mmap_write_lock(mm);
+	/* To stabilise kernel page tables we must hold the init_mm lock too. */
+	if (mm != &init_mm)
+		mmap_write_lock_nested(&init_mm, SINGLE_DEPTH_NESTING);
+
 	while (range->start != range->end) {
 		walk_page_range_debug(mm, range->start, range->end,
 				      &ptdump_ops, pgd, st);
 		range++;
 	}
+
+	if (mm != &init_mm)
+		mmap_write_unlock(&init_mm);
 	mmap_write_unlock(mm);
 	put_online_mems();
 
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 1afca3568b9b65..f4fa227a8d7f04 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -43,6 +43,7 @@
 #include <asm/tlbflush.h>
 #include <asm/shmparam.h>
 #include <linux/page_owner.h>
+#include <linux/cleanup.h>
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/vmalloc.h>
@@ -158,10 +159,21 @@ static int vmap_try_huge_pmd(pmd_t *pmd, unsigned long addr, unsigned long end,
 	if (!IS_ALIGNED(phys_addr, PMD_SIZE))
 		return 0;
 
-	if (pmd_present(*pmd) && !pmd_free_pte_page(pmd, addr))
-		return 0;
+	if (!pmd_present(*pmd))
+		return pmd_set_huge(pmd, phys_addr, prot);
 
-	return pmd_set_huge(pmd, phys_addr, prot);
+	/*
+	 * Acquire the mmap read lock to exclude ptdump, which walks
+	 * kernel page tables it does not own under the mmap write lock.
+	 *
+	 * Concurrent read lock holders are safe: each exclusively owns
+	 * the range it operates on and cannot reach this page table.
+	 */
+	scoped_cond_guard(mmap_read_lock_try, return 0, &init_mm) {
+		if (!pmd_free_pte_page(pmd, addr))
+			return 0;
+		return pmd_set_huge(pmd, phys_addr, prot);
+	}
 }
 
 static int vmap_pmd_range(pud_t *pud, unsigned long addr, unsigned long end,
@@ -210,10 +222,15 @@ static int vmap_try_huge_pud(pud_t *pud, unsigned long addr, unsigned long end,
 	if (!IS_ALIGNED(phys_addr, PUD_SIZE))
 		return 0;
 
-	if (pud_present(*pud) && !pud_free_pmd_page(pud, addr))
-		return 0;
+	if (!pud_present(*pud))
+		return pud_set_huge(pud, phys_addr, prot);
 
-	return pud_set_huge(pud, phys_addr, prot);
+	/* See comment in vmap_try_huge_pmd(). */
+	scoped_cond_guard(mmap_read_lock_try, return 0, &init_mm) {
+		if (!pud_free_pmd_page(pud, addr))
+			return 0;
+		return pud_set_huge(pud, phys_addr, prot);
+	}
 }
 
 static int vmap_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end,
@@ -262,10 +279,15 @@ static int vmap_try_huge_p4d(p4d_t *p4d, unsigned long addr, unsigned long end,
 	if (!IS_ALIGNED(phys_addr, P4D_SIZE))
 		return 0;
 
-	if (p4d_present(*p4d) && !p4d_free_pud_page(p4d, addr))
-		return 0;
+	if (!p4d_present(*p4d))
+		return p4d_set_huge(p4d, phys_addr, prot);
 
-	return p4d_set_huge(p4d, phys_addr, prot);
+	/* See comment in vmap_try_huge_pmd(). */
+	scoped_cond_guard(mmap_read_lock_try, return 0, &init_mm) {
+		if (!p4d_free_pud_page(p4d, addr))
+			return 0;
+		return p4d_set_huge(p4d, phys_addr, prot);
+	}
 }
 
 static int vmap_p4d_range(pgd_t *pgd, unsigned long addr, unsigned long end,

gemini-3.1-pro-preview

null

null

							input: 6648
							output: 18
							thoughts: 553
						

**Analyzing a Synchronization Change in Core Kernel Memory Management**

Okay, so I'm looking at this patch and my initial thought is, this is a pretty significant change. We're talking about synchronization within critical areas: page table dumping (ptdump), vmalloc, and CPA code. It looks like they're replacing a static key approach on arm64 with `init_mm.mmap_lock` and adding locking in x86 for CPA and vmalloc huge page setup. This is a solid move, replacing a potential weak spot with something more robust.

Let's break down the actual changes. Specifically, on arm64, it looks like they are removing the `arm64_ptdump_lock_key` static key logic in `pmd_free_pte_page` and `pud_free_pmd_page`, along with removal of `arm64_ptdump_walk_pgd`. Then, x86 is getting `mmap_write_lock` and `mmap_read_lock` around CPA collapse and `__change_page_attr_set_clr` calls. Then in `mm/pagewalk.c` and `mm/ptdump.c` they're updating `walk_page_range_debug` and `ptdump_walk_pgd`, respectively, to use the `init_mm.mmap_lock`. Finally, in `mm/vmalloc.c`, the patch adds `scoped_cond_guard` that attempts an `mmap_read_lock` around the `vmap_try_huge_*` functions.

This means it's a functional change, a pretty deep one, as it touches core memory management components. And it's reachable code, which means we *absolutely* need to fuzz it. We've got to make sure this doesn't introduce any new races or locking issues. We can't let something like this slip by, so we're going to need to look carefully at those functions I noted: `vmap_try_huge_pmd`, `vmap_try_huge_pud`, `vmap_try_huge_p4d`, `cpa_collapse_large_pages`, `change_page_attr_set_clr`, `ptdump_walk_pgd`, `walk_page_range_debug`, `pmd_free_pte_page`, and `pud_free_pmd_page`. These are our primary targets for testing and analysis.

Wait a second, ptdump… wasn't that triggered through debugfs? I need to check if we require any special `PTDUMP` configurations to trigger this. I'll search the Kconfig to see if we need a specific config to enable it.

{
  "Expression": "config PTDUMP"
}

{
  "Output": "arch/arm64/kvm/Kconfig=45=if KVM\narch/arm64/kvm/Kconfig-46-\narch/arm64/kvm/Kconfig:47:config PTDUMP_STAGE2_DEBUGFS\narch/arm64/kvm/Kconfig-48-\tbool \"Present the stage-2 pagetables to debugfs\"\n--\nmm/Kconfig.debug=216=config ARCH_HAS_PTDUMP\n--\nmm/Kconfig.debug-218-\nmm/Kconfig.debug:219:config PTDUMP\nmm/Kconfig.debug-220-\tbool\nmm/Kconfig.debug-221-\nmm/Kconfig.debug:222:config PTDUMP_DEBUGFS\nmm/Kconfig.debug-223-\tbool \"Export kernel pagetable layout to userspace via debugfs\"\n"
}

gemini-3.1-pro-preview

null

null

							input: 8034
							output: 20
							thoughts: 31
						

Okay, here's my interpretation of those thoughts, tailored for an expert audience, presented in the first person:

**Investigating the ptdump Configuration**

Alright, so `PTDUMP_DEBUGFS` is the key to enabling ptdump, got it. Now, my first move is to dig into its dependencies. I need to understand what other configurations need to be in place, what base features it relies on. I'm thinking build options, kernel features – that kind of thing. Let's see how deep this rabbit hole goes before I start experimenting.

{
  "Expression": "config PTDUMP_DEBUGFS"
}

{
  "Output": "mm/Kconfig.debug=219=config PTDUMP\n--\nmm/Kconfig.debug-221-\nmm/Kconfig.debug:222:config PTDUMP_DEBUGFS\nmm/Kconfig.debug-223-\tbool \"Export kernel pagetable layout to userspace via debugfs\"\n"
}

gemini-3.1-pro-preview

null

null

							input: 8291
							output: 34
							thoughts: 19
						

Here's my attempt at summarizing the thought process, tailored for an expert audience:

**Diving into Debugging Configuration**

Okay, so I'm thinking, where's the best place to start looking into these debug options? My instinct is to check the `mm/Kconfig.debug` file. Specifically, I'm going to jump to around line 222. I'm hoping that's where the core of these debugging-related configurations is defined. That section likely contains the dependencies, help text, and default settings that I need to understand to manipulate the behavior I'm after. It's the usual route when chasing down these kinds of configurations, the Kconfig files usually keep a good track record of how these are implemented.

{
  "File": "mm/Kconfig.debug",
  "FirstLine": 215,
  "LineCount": 20
}

{
  "Contents": " 215:\t\n 216:\tconfig ARCH_HAS_PTDUMP\n 217:\t\tbool\n 218:\t\n 219:\tconfig PTDUMP\n 220:\t\tbool\n 221:\t\n 222:\tconfig PTDUMP_DEBUGFS\n 223:\t\tbool \"Export kernel pagetable layout to userspace via debugfs\"\n 224:\t\tdepends on DEBUG_KERNEL\n 225:\t\tdepends on DEBUG_FS\n 226:\t\tdepends on ARCH_HAS_PTDUMP\n 227:\t\tselect PTDUMP\n 228:\t\thelp\n 229:\t\t  Say Y here if you want to show the kernel pagetable layout in a\n 230:\t\t  debugfs file. This information is only useful for kernel developers\n 231:\t\t  who are working in architecture specific areas of the kernel.\n 232:\t\t  It is probably not a good idea to enable this feature in a production\n 233:\t\t  kernel.\n 234:\t\n"
}

gemini-3.1-pro-preview

null

null

							input: 8772
							output: 18
							thoughts: 33
						

Okay, here's my take on those thoughts, framed as an expert's internal monologue:

**Investigating Debugging Options**

Right, so I need to get a deeper look at what's going on... the initial thought is, `PTDUMP_DEBUGFS` seems to be the key configuration option to enable for that kind of detailed debugging. I need to make sure I have that toggled on. Now, a nagging memory... I seem to recall that the `DEBUG_WX` functionality sometimes leverages the `ptdump` capabilities. It makes sense, given what `DEBUG_WX` is supposed to achieve. Okay, better verify that relationship directly. I'll need to double check how they interrelate to be certain of my path forward.

{
  "Expression": "config DEBUG_WX"
}

{
  "Output": "mm/Kconfig.debug=183=config ARCH_HAS_DEBUG_WX\n--\nmm/Kconfig.debug-185-\nmm/Kconfig.debug:186:config DEBUG_WX\nmm/Kconfig.debug-187-\tbool \"Warn on W+X mappings at boot\"\n"
}

gemini-3.1-pro-preview

null

null

							input: 9067
							output: 34
							thoughts: 19
						

Here's a summary of my thought process, as requested:

**Diving into Debugging Configuration**

Okay, time to get my hands dirty. I need to understand something related to the debugging configuration of this system. The logical place to start is `mm/Kconfig.debug`. I recall this file usually houses the Kconfig options specific to memory management debugging features. Let's navigate to around line 186. I'm guessing that line or the surrounding lines will have the key to what I'm looking for - a specific feature or a related conditional that governs its inclusion or exclusion.

{
  "File": "mm/Kconfig.debug",
  "FirstLine": 180,
  "LineCount": 20
}

{
  "Contents": " 180:\t\thelp\n 181:\t\t  This option enables a testcase for the setting rodata read-only.\n 182:\t\n 183:\tconfig ARCH_HAS_DEBUG_WX\n 184:\t\tbool\n 185:\t\n 186:\tconfig DEBUG_WX\n 187:\t\tbool \"Warn on W+X mappings at boot\"\n 188:\t\tdepends on ARCH_HAS_DEBUG_WX\n 189:\t\tdepends on ARCH_HAS_PTDUMP\n 190:\t\tdepends on MMU\n 191:\t\tselect PTDUMP\n 192:\t\thelp\n 193:\t\t  Generate a warning if any W+X mappings are found at boot.\n 194:\t\n 195:\t\t  This is useful for discovering cases where the kernel is leaving W+X\n 196:\t\t  mappings after applying NX, as such mappings are a security risk.\n 197:\t\n 198:\t\t  Look for a message in dmesg output like this:\n 199:\t\n"
}

gemini-3.1-pro-preview

null

null

							input: 9524
							output: 24
							thoughts: 30
						

Here's my take on the thought process:

**Investigating Configuration Dependencies**

Okay, so I see that setting `DEBUG_WX` also automatically enables `PTDUMP`. That's interesting, I need to keep that in mind as I go forward. Now, the next question that's top of mind is to check if we have any other configuration options that are tied to vmalloc huge pages. It's important to understand the relationships between different configurations and how they affect the system, particularly when dealing with memory management. I need to make sure I haven't missed anything that could influence behavior. Let's dig deeper.

{
  "Expression": "config HAVE_ARCH_HUGE_VMALLOC"
}

{
  "Output": "arch/Kconfig=1092=config HAVE_ARCH_HUGE_VMAP\n--\narch/Kconfig-1099-#\narch/Kconfig:1100:config HAVE_ARCH_HUGE_VMALLOC\narch/Kconfig-1101-\tdepends on HAVE_ARCH_HUGE_VMAP\n"
}

gemini-3.1-pro-preview

null

null

							input: 9801
							output: 33
							thoughts: 18
						

Okay, let's dive into this. Here's my thought process on the matter:

**Navigating the Kernel Configuration Landscape**

Right, I need to get my bearings. The task at hand likely involves understanding or modifying some kernel configuration options.  Given the context, I think the most relevant place to start is the `arch/Kconfig` file. I'll need to drill down into how the architecture-specific configuration is handled.

Based on my understanding of how these projects are organized, `Kconfig` files are the central drivers for the menuconfig interface. I will head straight to line 1100. This is probably a good starting point for the section I'm looking for - a module, feature or group of options related to my area of focus. I'll try to understand the surrounding context of that line. From there, I'll be able to work backwards through dependencies, if necessary, and see how this configuration option ties into the bigger picture. This will give me the information I need to fulfill whatever requirements I'm tackling.

{
  "File": "arch/Kconfig",
  "FirstLine": 1090,
  "LineCount": 20
}

{
  "Contents": "1090:\t\tbool\n1091:\t\n1092:\tconfig HAVE_ARCH_HUGE_VMAP\n1093:\t\tbool\n1094:\t\n1095:\t#\n1096:\t#  Archs that select this would be capable of PMD-sized vmaps (i.e.,\n1097:\t#  arch_vmap_pmd_supported() returns true). The VM_ALLOW_HUGE_VMAP flag\n1098:\t#  must be used to enable allocations to use hugepages.\n1099:\t#\n1100:\tconfig HAVE_ARCH_HUGE_VMALLOC\n1101:\t\tdepends on HAVE_ARCH_HUGE_VMAP\n1102:\t\tbool\n1103:\t\n1104:\tconfig ARCH_WANT_HUGE_PMD_SHARE\n1105:\t\tbool\n1106:\t\n1107:\t# Archs that want to use pmd_mkwrite on kernel memory need it defined even\n1108:\t# if there are no userspace memory management features that use it\n1109:\tconfig ARCH_WANT_KERNEL_PMD_MKWRITE\n"
}

gemini-3.1-pro-preview

null

null

							input: 10383
							output: 21
							thoughts: 33
						

Okay, here's my interpretation of those thoughts, tailored for an expert audience, and presented as if they were my own:

**Investigating Huge vmalloc Configuration**

Hmm, let's see...I'm digging into the kernel memory management. Right, so `HAVE_ARCH_HUGE_VMALLOC` is a bit of a sneaky one. It's not a straightforward option you see in the main config menus, is it? It's architecture-specific, typically selected implicitly based on the underlying hardware capabilities.

The real question I need answered is: is there an *explicit* configuration option that I can tweak, to actually *enable* or influence the behavior of huge vmalloc? I know that on some architectures you might have something like `CONFIG_HUGETLB_VMALLOC` to turn it on, but what about the broader scope? Do I need to look for a dependency, some other arch-specific flag, or perhaps something new entirely? I wonder what the dependencies are, and are there some specific architectures, with which I am more familiar, to check?

{
  "Expression": "config.*HUGE_VMALLOC"
}

{
  "Output": "arch/Kconfig=1092=config HAVE_ARCH_HUGE_VMAP\n--\narch/Kconfig-1099-#\narch/Kconfig:1100:config HAVE_ARCH_HUGE_VMALLOC\narch/Kconfig-1101-\tdepends on HAVE_ARCH_HUGE_VMAP\n"
}

gemini-3.1-pro-preview

null

null

							input: 10754
							output: 21
							thoughts: 11
						

Okay, here's my interpretation of that thought process, assuming I'm deep in my domain of expertise:

**Checking `HUGE_VMAP`**

Alright, time to dive into this. The mental gears are already turning. "Check `HUGE_VMAP`" – that's a pretty specific directive. My immediate thought is, "Okay, why are we looking at the `HUGE_VMAP`? What problem are we trying to solve, or what aspect of the system are we currently investigating?". I'm already anticipating the context. This likely relates to virtual memory management, specifically large pages. Is there a memory allocation issue? Performance bottleneck? Unexpected behavior related to huge pages being used (or not being used) as expected?

I'm thinking about the tools and methods I'd likely use. Am I pulling from the debugging tools to run in real-time mode? Am I going back to previous logs to find the cause? Perhaps I have a script that generates a report?

Specifically, I'm considering what data I will be looking for: The size of the `HUGE_VMAP`, its current usage, any fragmentation, and any relevant error messages. I'll need to correlate the state of the VMAP with the other memory subsystems in the system. I'm already formulating my hypothesis: perhaps there's a misconfiguration of huge page reservations, or a resource constraint limiting the allocation of large pages, leading to performance degradation or even application crashes. I know from experience that this kind of issue can be subtle and require a nuanced understanding of memory allocation strategies and system architecture. Let's get to work!

{
  "Expression": "config.*HUGE_VMAP"
}

{
  "Output": "Documentation/features/vm/huge-vmap/arch-support.txt-2-# Feature name:          huge-vmap\nDocumentation/features/vm/huge-vmap/arch-support.txt:3:#         Kconfig:       HAVE_ARCH_HUGE_VMAP\nDocumentation/features/vm/huge-vmap/arch-support.txt-4-#         description:   arch supports the arch_vmap_pud_supported() and arch_vmap_pmd_supported() VM APIs\n--\narch/Kconfig=1089=config HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD\n--\narch/Kconfig-1091-\narch/Kconfig:1092:config HAVE_ARCH_HUGE_VMAP\narch/Kconfig-1093-\tbool\n"
}

gemini-3.1-pro-preview

null

null

							input: 11330
							output: 18
							thoughts: 41
						

Okay, here's my interpretation of those thoughts, presented as a personal thought process, as requested:

**Vmalloc, CPA, and the Architecture Dance**

Right, so, my initial thought is that huge vmalloc is enabled by default on architectures that can actually handle it. That's good, efficient memory management is key. But then, my mind jumps to something more targeted: CPA, or `change_page_attr`. It's definitely an x86 thing, isn't it? My intuition is screaming "x86 specific" and I need to check myself.

Now, my real question is: is there any configuration option? Any relevant Kconfig entry, maybe? I need to know if there's any way to control CPA's behavior, toggle it on or off, or adjust its parameters. Knowing that will be pivotal for adapting this to specific systems. I need to dig into the config options to see what control I have.

{
  "Expression": "config.*CPA"
}

{
  "Output": "Documentation/networking/ethtool-netlink.rst=1509=FEC_GET\n--\nDocumentation/networking/ethtool-netlink.rst-1511-\nDocumentation/networking/ethtool-netlink.rst:1512:Gets FEC configuration and state like ``ETHTOOL_GFECPARAM`` ioctl request.\nDocumentation/networking/ethtool-netlink.rst-1513-\n--\narch/x86/Kconfig=1466=config X86_DIRECT_GBPAGES\n--\narch/x86/Kconfig-1474-\narch/x86/Kconfig:1475:config X86_CPA_STATISTICS\narch/x86/Kconfig-1476-\tbool \"Enable statistic for Change Page Attribute\"\n--\narch/x86/Kconfig.debug=153=config DEBUG_BOOT_PARAMS\n--\narch/x86/Kconfig.debug-159-\narch/x86/Kconfig.debug:160:config CPA_DEBUG\narch/x86/Kconfig.debug-161-\tbool \"CPA self-test code\"\n"
}

gemini-3.1-pro-preview

null

null

							input: 11882
							output: 38
							thoughts: 33
						

Here's my take on the thought process:

**Diving into Potential Debugging Aids**

Okay, so I'm thinking about how to approach this... `CPA_DEBUG` might be a useful tool here. I recall seeing that flag somewhere and now's the time to investigate. To get a better handle on how it works, I should probably check out `arch/x86/Kconfig.debug`. I seem to remember it being defined around line 160. That's a good starting point to understand its scope and implications within the x86 architecture, and whether it's relevant to the current issue. Let me grab the source and have a quick look.

{
  "File": "arch/x86/Kconfig.debug",
  "FirstLine": 155,
  "LineCount": 20
}

{
  "Contents": " 155:\t\tdepends on DEBUG_KERNEL\n 156:\t\tdepends on DEBUG_FS\n 157:\t\thelp\n 158:\t\t  This option will cause struct boot_params to be exported via debugfs.\n 159:\t\n 160:\tconfig CPA_DEBUG\n 161:\t\tbool \"CPA self-test code\"\n 162:\t\tdepends on DEBUG_KERNEL\n 163:\t\thelp\n 164:\t\t  Do change_page_attr() self-tests every 30 seconds.\n 165:\t\n 166:\tconfig DEBUG_ENTRY\n 167:\t\tbool \"Debug low-level entry code\"\n 168:\t\tdepends on DEBUG_KERNEL\n 169:\t\thelp\n 170:\t\t  This option enables sanity checks in x86's low-level entry code.\n 171:\t\t  Some of these sanity checks may slow down kernel entries and\n 172:\t\t  exits or otherwise impact performance.\n 173:\t\n 174:\t\t  If unsure, say N.\n"
}

gemini-3.1-pro-preview

null

null

							input: 12379
							output: 22
							thoughts: 266
						

**My Fuzzing Strategy for CPA**

Okay, so `CPA_DEBUG` has this neat trick where it runs `change_page_attr()` self-tests every 30 seconds. That's fantastic! This gives me a solid opportunity for fuzzing CPA.

The first step here is to ensure I've enabled the right configurations: `PTDUMP_DEBUGFS`, `DEBUG_WX`, and, of course, `CPA_DEBUG`. Those are essential.

Now, let's look at key symbols to target. I'm focusing on these for now: `vmap_try_huge_pmd`, `vmap_try_huge_pud`, `vmap_try_huge_p4d`, `cpa_collapse_large_pages`, `change_page_attr_set_clr`, `ptdump_walk_pgd`, `walk_page_range_debug`, `pmd_free_pte_page`, and `pud_free_pmd_page`.

I should probably double-check the definitions of `pmd_free_pte_page` and `pud_free_pmd_page` just to be sure. A quick search reveals that they are in `arch/arm64/mm/mmu.c`. Ah, and wait, `vmap_try_huge_pmd` calls `pmd_free_pte_page`, which could be interesting. Now, is `pmd_free_pte_page` defined *only* for ARM64? I have to consider other architectures for broader coverage.

{
  "Expression": "pmd_free_pte_page"
}

{
  "Output": "arch/arm64/mm/mmu.c=1857=int pmd_clear_huge(pmd_t *pmdp)\n--\narch/arm64/mm/mmu.c-1864-\narch/arm64/mm/mmu.c:1865:int pmd_free_pte_page(pmd_t *pmdp, unsigned long addr)\narch/arm64/mm/mmu.c-1866-{\n--\narch/arm64/mm/mmu.c=1884=int pud_free_pmd_page(pud_t *pudp, unsigned long addr)\n--\narch/arm64/mm/mmu.c-1903-\t\tif (pmd_present(pmdp_get(pmdp)))\narch/arm64/mm/mmu.c:1904:\t\t\tpmd_free_pte_page(pmdp, next);\narch/arm64/mm/mmu.c-1905-\t} while (pmdp++, next += PMD_SIZE, next != end);\n--\narch/powerpc/mm/book3s64/radix_pgtable.c=1675=int pmd_clear_huge(pmd_t *pmd)\n--\narch/powerpc/mm/book3s64/radix_pgtable.c-1684-\narch/powerpc/mm/book3s64/radix_pgtable.c:1685:int pmd_free_pte_page(pmd_t *pmd, unsigned long addr)\narch/powerpc/mm/book3s64/radix_pgtable.c-1686-{\n--\narch/riscv/mm/pgtable.c=117=int pmd_clear_huge(pmd_t *pmd)\n--\narch/riscv/mm/pgtable.c-124-\narch/riscv/mm/pgtable.c:125:int pmd_free_pte_page(pmd_t *pmd, unsigned long addr)\narch/riscv/mm/pgtable.c-126-{\n--\narch/x86/mm/pgtable.c=718=int pud_free_pmd_page(pud_t *pud, unsigned long addr)\n--\narch/x86/mm/pgtable.c-754-/**\narch/x86/mm/pgtable.c:755: * pmd_free_pte_page - Clear PMD entry and free PTE page.\narch/x86/mm/pgtable.c-756- * @pmd: Pointer to the PMD\n--\narch/x86/mm/pgtable.c-761- */\narch/x86/mm/pgtable.c:762:int pmd_free_pte_page(pmd_t *pmd, unsigned long addr)\narch/x86/mm/pgtable.c-763-{\n--\narch/x86/mm/pgtable.c-782- */\narch/x86/mm/pgtable.c:783:int pmd_free_pte_page(pmd_t *pmd, unsigned long addr)\narch/x86/mm/pgtable.c-784-{\n--\ninclude/linux/pgtable.h=2176=int pud_free_pmd_page(pud_t *pud, unsigned long addr);\ninclude/linux/pgtable.h:2177:int pmd_free_pte_page(pmd_t *pmd, unsigned long addr);\ninclude/linux/pgtable.h-2178-#else\t/* !CONFIG_HAVE_ARCH_HUGE_VMAP */\n--\ninclude/linux/pgtable.h=2204=static inline int pud_free_pmd_page(pud_t *pud, unsigned long addr)\n--\ninclude/linux/pgtable.h-2207-}\ninclude/linux/pgtable.h:2208:static inline int pmd_free_pte_page(pmd_t *pmd, unsigned long addr)\ninclude/linux/pgtable.h-2209-{\n--\nmm/vmalloc.c=143=static int vmap_try_huge_pmd(pmd_t *pmd, unsigned long addr, unsigned long end,\n--\nmm/vmalloc.c-172-\tscoped_cond_guard(mmap_read_lock_try, return 0, \u0026init_mm) {\nmm/vmalloc.c:173:\t\tif (!pmd_free_pte_page(pmd, addr))\nmm/vmalloc.c-174-\t\t\treturn 0;\n"
}

gemini-3.1-pro-preview

null

null

							input: 14182
							output: 22
							thoughts: 328
						

**Analyzing the Patch's Scope**

Okay, so I'm looking at this patch and initially thought it was just focused on architecture-specific functions, since the entry point seems to be from `mm/vmalloc.c`. But hold on, the changes are actually broader than that. I see modifications in `arch/arm64/mm/mmu.c`, specifically to `pmd_free_pte_page` and `pud_free_pmd_page`. And then there's the x86 side, with `arch/x86/mm/pat/set_memory.c` changing `cpa_collapse_large_pages` and `change_page_attr_set_clr`. Also, it touches quite a few other areas, including `mm/pagewalk.c`, `mm/ptdump.c` and `mm/vmalloc.c` as expected.

Therefore, the key symbols this patch is dealing with are: `vmap_try_huge_pmd`, `vmap_try_huge_pud`, `vmap_try_huge_p4d`, `cpa_collapse_large_pages`, `change_page_attr_set_clr`, `ptdump_walk_pgd`, `walk_page_range_debug`, `pmd_free_pte_page`, and `pud_free_pmd_page`. I should really focus my attention on understanding how the changes to these functions impact the overall memory management flow.

Now, a quick note, I see that `cpa_collapse_large_pages` is static within `arch/x86/mm/pat/set_memory.c`. Given that it's static, I should verify its reachability to ensure it's actually being used. Let me check if it's called from something like `__cpa_flush_tlb` or something similar, and then I'll be able to determine the overall impact.

{
  "Expression": "cpa_collapse_large_pages"
}

{
  "Output": "arch/x86/mm/pat/set_memory.c=412=static int collapse_large_pages(unsigned long addr, struct list_head *pgtables);\narch/x86/mm/pat/set_memory.c-413-\narch/x86/mm/pat/set_memory.c:414:static void __cpa_collapse_large_pages(struct cpa_data *cpa)\narch/x86/mm/pat/set_memory.c-415-{\n--\narch/x86/mm/pat/set_memory.c-445-\narch/x86/mm/pat/set_memory.c:446:static void cpa_collapse_large_pages(struct cpa_data *cpa)\narch/x86/mm/pat/set_memory.c-447-{\n--\narch/x86/mm/pat/set_memory.c-454-\tscoped_guard(mmap_write_lock, \u0026init_mm)\narch/x86/mm/pat/set_memory.c:455:\t\t__cpa_collapse_large_pages(cpa);\narch/x86/mm/pat/set_memory.c-456-}\n--\narch/x86/mm/pat/set_memory.c=458=static void cpa_flush(struct cpa_data *cpa, int cache)\n--\narch/x86/mm/pat/set_memory.c-493-\tif (cpa-\u003eflags \u0026 CPA_COLLAPSE)\narch/x86/mm/pat/set_memory.c:494:\t\tcpa_collapse_large_pages(cpa);\narch/x86/mm/pat/set_memory.c-495-}\n"
}

gemini-3.1-pro-preview

null

null

							input: 15407
							output: 23
							thoughts: 62
						

Okay, let's see...

**Analyzing the CPA Call Chain**

Right, so `cpa_collapse_large_pages` is definitely being invoked by `cpa_flush`. That's good to have confirmed. And as I suspected, `change_page_attr_set_clr` is the core function, the starting point for everything related to CPA. Now, I need to check something quickly. I need to make sure `vmap_try_huge_pmd` is declared statically. Let me just verify that.

{
  "Expression": "vmap_try_huge_pmd"
}

{
  "Output": "mm/vmalloc.c=95=static int vmap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,\n--\nmm/vmalloc.c-142-\nmm/vmalloc.c:143:static int vmap_try_huge_pmd(pmd_t *pmd, unsigned long addr, unsigned long end,\nmm/vmalloc.c-144-\t\t\tphys_addr_t phys_addr, pgprot_t prot,\n--\nmm/vmalloc.c=179=static int vmap_pmd_range(pud_t *pud, unsigned long addr, unsigned long end,\n--\nmm/vmalloc.c-192-\nmm/vmalloc.c:193:\t\tif (vmap_try_huge_pmd(pmd, addr, next, phys_addr, prot,\nmm/vmalloc.c-194-\t\t\t\t\tmax_page_shift)) {\n--\nmm/vmalloc.c=206=static int vmap_try_huge_pud(pud_t *pud, unsigned long addr, unsigned long end,\n--\nmm/vmalloc.c-227-\nmm/vmalloc.c:228:\t/* See comment in vmap_try_huge_pmd(). */\nmm/vmalloc.c-229-\tscoped_cond_guard(mmap_read_lock_try, return 0, \u0026init_mm) {\n--\nmm/vmalloc.c=263=static int vmap_try_huge_p4d(p4d_t *p4d, unsigned long addr, unsigned long end,\n--\nmm/vmalloc.c-284-\nmm/vmalloc.c:285:\t/* See comment in vmap_try_huge_pmd(). */\nmm/vmalloc.c-286-\tscoped_cond_guard(mmap_read_lock_try, return 0, \u0026init_mm) {\n"
}

gemini-3.1-pro-preview

null

null

							input: 16095
							output: 21
							thoughts: 138
						

Okay, here's my take on those thoughts, as if they were mine:

**Static Analysis and Potential Hotspots**

Right, this feels pretty static, on the surface. I'm focusing on some key symbols, I see these as potential hot spots for memory management and page table manipulations. Specifically, I'm thinking about: `vmap_try_huge_pmd`, `vmap_try_huge_pud`, `vmap_try_huge_p4d` – the huge page allocation attempts within vmalloc space. Then there's `cpa_collapse_large_pages` and `change_page_attr_set_clr`, both of which scream potential contention or performance bottlenecks related to page attribute modifications and large page collapsing. Also, I've got `ptdump_walk_pgd`, `walk_page_range_debug`, `pmd_free_pte_page`, and `pud_free_pmd_page`, which are all pointing me toward page table walking, debugging, and deallocation paths. All of these seem to represent critical functions for large memory management.

Wait a second… `ptdump_walk_pgd` is exported? That’s interesting. I hadn't realized that was exposed. This means it might be used by external modules. I need to make sure to consider potential dependencies on those functionalities as well.

{
  "Expression": "ptdump_walk_pgd"
}

{
  "Output": "arch/arm/include/asm/ptdump.h=16=struct ptdump_info {\n--\narch/arm/include/asm/ptdump.h-21-\narch/arm/include/asm/ptdump.h:22:void ptdump_walk_pgd(struct seq_file *s, struct ptdump_info *info);\narch/arm/include/asm/ptdump.h-23-#ifdef CONFIG_ARM_PTDUMP_DEBUGFS\n--\narch/arm/mm/dump.c=398=static void walk_pgd(struct pg_state *st, struct mm_struct *mm,\n--\narch/arm/mm/dump.c-414-\narch/arm/mm/dump.c:415:void ptdump_walk_pgd(struct seq_file *m, struct ptdump_info *info)\narch/arm/mm/dump.c-416-{\n--\narch/arm/mm/ptdump_debugfs.c=7=static int ptdump_show(struct seq_file *m, void *v)\n--\narch/arm/mm/ptdump_debugfs.c-10-\narch/arm/mm/ptdump_debugfs.c:11:\tptdump_walk_pgd(m, info);\narch/arm/mm/ptdump_debugfs.c-12-\treturn 0;\n--\narch/arm64/mm/ptdump.c=286=void ptdump_walk(struct seq_file *s, struct ptdump_info *info)\n--\narch/arm64/mm/ptdump.c-313-\narch/arm64/mm/ptdump.c:314:\tptdump_walk_pgd(\u0026st.ptdump, info-\u003emm, NULL);\narch/arm64/mm/ptdump.c-315-}\n--\narch/arm64/mm/ptdump.c=331=bool ptdump_check_wx(void)\n--\narch/arm64/mm/ptdump.c-355-\narch/arm64/mm/ptdump.c:356:\tptdump_walk_pgd(\u0026st.ptdump, \u0026init_mm, NULL);\narch/arm64/mm/ptdump.c-357-\n--\narch/powerpc/mm/ptdump/ptdump.c=334=static int ptdump_show(struct seq_file *m, void *v)\n--\narch/powerpc/mm/ptdump/ptdump.c-351-\t/* Traverse kernel page tables */\narch/powerpc/mm/ptdump/ptdump.c:352:\tptdump_walk_pgd(\u0026st.ptdump, \u0026init_mm, NULL);\narch/powerpc/mm/ptdump/ptdump.c-353-\treturn 0;\n--\narch/powerpc/mm/ptdump/ptdump.c=368=bool ptdump_check_wx(void)\n--\narch/powerpc/mm/ptdump/ptdump.c-391-\narch/powerpc/mm/ptdump/ptdump.c:392:\tptdump_walk_pgd(\u0026st.ptdump, \u0026init_mm, NULL);\narch/powerpc/mm/ptdump/ptdump.c-393-\n--\narch/riscv/mm/ptdump.c=353=static void ptdump_walk(struct seq_file *s, struct ptd_mm_info *pinfo)\n--\narch/riscv/mm/ptdump.c-372-\narch/riscv/mm/ptdump.c:373:\tptdump_walk_pgd(\u0026st.ptdump, pinfo-\u003emm, NULL);\narch/riscv/mm/ptdump.c-374-}\n--\narch/riscv/mm/ptdump.c=376=bool ptdump_check_wx(void)\n--\narch/riscv/mm/ptdump.c-399-\narch/riscv/mm/ptdump.c:400:\tptdump_walk_pgd(\u0026st.ptdump, \u0026init_mm, NULL);\narch/riscv/mm/ptdump.c-401-\n--\narch/s390/mm/dump_pagetables.c=182=bool ptdump_check_wx(void)\n--\narch/s390/mm/dump_pagetables.c-210-\t\treturn true;\narch/s390/mm/dump_pagetables.c:211:\tptdump_walk_pgd(\u0026st.ptdump, \u0026init_mm, NULL);\narch/s390/mm/dump_pagetables.c-212-\tif (st.wx_pages) {\n--\narch/s390/mm/dump_pagetables.c=226=static int ptdump_show(struct seq_file *m, void *v)\n--\narch/s390/mm/dump_pagetables.c-250-\tmutex_lock(\u0026cpa_mutex);\narch/s390/mm/dump_pagetables.c:251:\tptdump_walk_pgd(\u0026st.ptdump, \u0026init_mm, NULL);\narch/s390/mm/dump_pagetables.c-252-\tmutex_unlock(\u0026cpa_mutex);\n--\narch/x86/include/asm/pgtable.h=30=struct seq_file;\narch/x86/include/asm/pgtable.h:31:void ptdump_walk_pgd_level(struct seq_file *m, struct mm_struct *mm);\narch/x86/include/asm/pgtable.h:32:void ptdump_walk_pgd_level_debugfs(struct seq_file *m, struct mm_struct *mm,\narch/x86/include/asm/pgtable.h-33-\t\t\t\t   bool user);\narch/x86/include/asm/pgtable.h:34:bool ptdump_walk_pgd_level_checkwx(void);\narch/x86/include/asm/pgtable.h:35:#define ptdump_check_wx ptdump_walk_pgd_level_checkwx\narch/x86/include/asm/pgtable.h-36-void ptdump_walk_user_pgd_level_checkwx(void);\n--\narch/x86/mm/debug_pagetables.c=8=static int ptdump_show(struct seq_file *m, void *v)\narch/x86/mm/debug_pagetables.c-9-{\narch/x86/mm/debug_pagetables.c:10:\tptdump_walk_pgd_level_debugfs(m, \u0026init_mm, false);\narch/x86/mm/debug_pagetables.c-11-\treturn 0;\n--\narch/x86/mm/debug_pagetables.c=16=static int ptdump_curknl_show(struct seq_file *m, void *v)\n--\narch/x86/mm/debug_pagetables.c-18-\tif (current-\u003emm-\u003epgd)\narch/x86/mm/debug_pagetables.c:19:\t\tptdump_walk_pgd_level_debugfs(m, current-\u003emm, false);\narch/x86/mm/debug_pagetables.c-20-\treturn 0;\n--\narch/x86/mm/debug_pagetables.c=26=static int ptdump_curusr_show(struct seq_file *m, void *v)\n--\narch/x86/mm/debug_pagetables.c-28-\tif (current-\u003emm-\u003epgd)\narch/x86/mm/debug_pagetables.c:29:\t\tptdump_walk_pgd_level_debugfs(m, current-\u003emm, true);\narch/x86/mm/debug_pagetables.c-30-\treturn 0;\n--\narch/x86/mm/debug_pagetables.c=37=static int ptdump_efi_show(struct seq_file *m, void *v)\n--\narch/x86/mm/debug_pagetables.c-39-\tif (efi_mm.pgd)\narch/x86/mm/debug_pagetables.c:40:\t\tptdump_walk_pgd_level_debugfs(m, \u0026efi_mm, false);\narch/x86/mm/debug_pagetables.c-41-\treturn 0;\n--\narch/x86/mm/dump_pagetables.c=416=static void note_page_flush(struct ptdump_state *pt_st)\n--\narch/x86/mm/dump_pagetables.c-422-\narch/x86/mm/dump_pagetables.c:423:bool ptdump_walk_pgd_level_core(struct seq_file *m,\narch/x86/mm/dump_pagetables.c-424-\t\t\t\tstruct mm_struct *mm, pgd_t *pgd,\n--\narch/x86/mm/dump_pagetables.c-457-\narch/x86/mm/dump_pagetables.c:458:\tptdump_walk_pgd(\u0026st.ptdump, mm, pgd);\narch/x86/mm/dump_pagetables.c-459-\n--\narch/x86/mm/dump_pagetables.c-473-\narch/x86/mm/dump_pagetables.c:474:void ptdump_walk_pgd_level(struct seq_file *m, struct mm_struct *mm)\narch/x86/mm/dump_pagetables.c-475-{\narch/x86/mm/dump_pagetables.c:476:\tptdump_walk_pgd_level_core(m, mm, mm-\u003epgd, false, true);\narch/x86/mm/dump_pagetables.c-477-}\narch/x86/mm/dump_pagetables.c-478-\narch/x86/mm/dump_pagetables.c:479:void ptdump_walk_pgd_level_debugfs(struct seq_file *m, struct mm_struct *mm,\narch/x86/mm/dump_pagetables.c-480-\t\t\t\t   bool user)\n--\narch/x86/mm/dump_pagetables.c-486-#endif\narch/x86/mm/dump_pagetables.c:487:\tptdump_walk_pgd_level_core(m, mm, pgd, false, false);\narch/x86/mm/dump_pagetables.c-488-}\n--\narch/x86/mm/dump_pagetables.c=490=void ptdump_walk_user_pgd_level_checkwx(void)\n--\narch/x86/mm/dump_pagetables.c-500-\tpgd = kernel_to_user_pgdp(pgd);\narch/x86/mm/dump_pagetables.c:501:\tptdump_walk_pgd_level_core(NULL, \u0026init_mm, pgd, true, false);\narch/x86/mm/dump_pagetables.c-502-#endif\n--\narch/x86/mm/dump_pagetables.c-504-\narch/x86/mm/dump_pagetables.c:505:bool ptdump_walk_pgd_level_checkwx(void)\narch/x86/mm/dump_pagetables.c-506-{\n--\narch/x86/mm/dump_pagetables.c-509-\narch/x86/mm/dump_pagetables.c:510:\treturn ptdump_walk_pgd_level_core(NULL, \u0026init_mm, INIT_PGD, true, false);\narch/x86/mm/dump_pagetables.c-511-}\n--\narch/x86/platform/efi/efi_32.c=75=void __init efi_dump_pagetable(void)\n--\narch/x86/platform/efi/efi_32.c-77-#ifdef CONFIG_EFI_PGT_DUMP\narch/x86/platform/efi/efi_32.c:78:\tptdump_walk_pgd_level(NULL, \u0026init_mm);\narch/x86/platform/efi/efi_32.c-79-#endif\n--\narch/x86/platform/efi/efi_64.c=423=void __init efi_dump_pagetable(void)\n--\narch/x86/platform/efi/efi_64.c-425-#ifdef CONFIG_EFI_PGT_DUMP\narch/x86/platform/efi/efi_64.c:426:\tptdump_walk_pgd_level(NULL, \u0026efi_mm);\narch/x86/platform/efi/efi_64.c-427-#endif\n--\ninclude/linux/ptdump.h=13=struct ptdump_state {\n--\ninclude/linux/ptdump.h-27-\ninclude/linux/ptdump.h:28:bool ptdump_walk_pgd_level_core(struct seq_file *m,\ninclude/linux/ptdump.h-29-\t\t\t\tstruct mm_struct *mm, pgd_t *pgd,\ninclude/linux/ptdump.h-30-\t\t\t\tbool checkwx, bool dmesg);\ninclude/linux/ptdump.h:31:void ptdump_walk_pgd(struct ptdump_state *st, struct mm_struct *mm, pgd_t *pgd);\ninclude/linux/ptdump.h-32-bool ptdump_check_wx(void);\n--\nmm/ptdump.c=166=static const struct mm_walk_ops ptdump_ops = {\n--\nmm/ptdump.c-174-\nmm/ptdump.c:175:void ptdump_walk_pgd(struct ptdump_state *st, struct mm_struct *mm, pgd_t *pgd)\nmm/ptdump.c-176-{\n"
}

gemini-3.1-pro-preview

null

null

							input: 20163
							output: 23
							thoughts: 79
						

Here's my summary, as I delve into this code:

**Analyzing `ptdump_walk_pgd` and Related Functions**

Okay, so `ptdump_walk_pgd` is defined in `mm/ptdump.c` and its declaration resides in `include/linux/ptdump.h`. Seems straightforward. Wait a second... it's declared globally but not explicitly exported to modules. That's a bit odd. I need to keep that in mind. Is it meant to be internal? Alright, let me shift gears and see how `change_page_attr_set_clr` is handled regarding its export status, as it's likely related. I'll need to check if the export is explicit, or if this is another function with similar nuances.

{
  "Expression": "change_page_attr_set_clr"
}

{
  "Output": "arch/x86/mm/pat/set_memory.c=1861=static int __change_page_attr(struct cpa_data *cpa, int primary)\n--\narch/x86/mm/pat/set_memory.c-1938-\narch/x86/mm/pat/set_memory.c:1939:static int __change_page_attr_set_clr(struct cpa_data *cpa, int primary);\narch/x86/mm/pat/set_memory.c-1940-\n--\narch/x86/mm/pat/set_memory.c=1944=static int cpa_process_alias(struct cpa_data *cpa)\n--\narch/x86/mm/pat/set_memory.c-1974-\narch/x86/mm/pat/set_memory.c:1975:\t\tret = __change_page_attr_set_clr(\u0026alias_cpa, 0);\narch/x86/mm/pat/set_memory.c-1976-\t\tif (ret)\n--\narch/x86/mm/pat/set_memory.c-2008-\t\t */\narch/x86/mm/pat/set_memory.c:2009:\t\t__change_page_attr_set_clr(\u0026alias_cpa, 0);\narch/x86/mm/pat/set_memory.c-2010-\t}\n--\narch/x86/mm/pat/set_memory.c-2015-\narch/x86/mm/pat/set_memory.c:2016:static int __change_page_attr_set_clr(struct cpa_data *cpa, int primary)\narch/x86/mm/pat/set_memory.c-2017-{\n--\narch/x86/mm/pat/set_memory.c-2068-\narch/x86/mm/pat/set_memory.c:2069:static int change_page_attr_set_clr(unsigned long *addr, int numpages,\narch/x86/mm/pat/set_memory.c-2070-\t\t\t\t    pgprot_t mask_set, pgprot_t mask_clr,\n--\narch/x86/mm/pat/set_memory.c-2126-\tscoped_guard(mmap_read_lock, \u0026init_mm)\narch/x86/mm/pat/set_memory.c:2127:\t\tret = __change_page_attr_set_clr(\u0026cpa, 1);\narch/x86/mm/pat/set_memory.c-2128-\n--\narch/x86/mm/pat/set_memory.c=2154=static inline int change_page_attr_set(unsigned long *addr, int numpages,\n--\narch/x86/mm/pat/set_memory.c-2156-{\narch/x86/mm/pat/set_memory.c:2157:\treturn change_page_attr_set_clr(addr, numpages, mask, __pgprot(0), 0,\narch/x86/mm/pat/set_memory.c-2158-\t\t(array ? CPA_ARRAY : 0), NULL);\n--\narch/x86/mm/pat/set_memory.c=2161=static inline int change_page_attr_clear(unsigned long *addr, int numpages,\n--\narch/x86/mm/pat/set_memory.c-2163-{\narch/x86/mm/pat/set_memory.c:2164:\treturn change_page_attr_set_clr(addr, numpages, __pgprot(0), mask, 0,\narch/x86/mm/pat/set_memory.c-2165-\t\t(array ? CPA_ARRAY : 0), NULL);\n--\narch/x86/mm/pat/set_memory.c=2168=static inline int cpa_set_pages_array(struct page **pages, int numpages,\n--\narch/x86/mm/pat/set_memory.c-2170-{\narch/x86/mm/pat/set_memory.c:2171:\treturn change_page_attr_set_clr(NULL, numpages, mask, __pgprot(0), 0,\narch/x86/mm/pat/set_memory.c-2172-\t\tCPA_PAGES_ARRAY, pages);\n--\narch/x86/mm/pat/set_memory.c=2175=static inline int cpa_clear_pages_array(struct page **pages, int numpages,\n--\narch/x86/mm/pat/set_memory.c-2177-{\narch/x86/mm/pat/set_memory.c:2178:\treturn change_page_attr_set_clr(NULL, numpages, __pgprot(0), mask, 0,\narch/x86/mm/pat/set_memory.c-2179-\t\tCPA_PAGES_ARRAY, pages);\n--\narch/x86/mm/pat/set_memory.c=2220=int _set_memory_wc(unsigned long addr, int numpages)\n--\narch/x86/mm/pat/set_memory.c-2227-\tif (!ret) {\narch/x86/mm/pat/set_memory.c:2228:\t\tret = change_page_attr_set_clr(\u0026addr, numpages,\narch/x86/mm/pat/set_memory.c-2229-\t\t\t\t\t       cachemode2pgprot(_PAGE_CACHE_MODE_WC),\n--\narch/x86/mm/pat/set_memory.c=2341=int set_memory_rox(unsigned long addr, int numpages)\n--\narch/x86/mm/pat/set_memory.c-2347-\narch/x86/mm/pat/set_memory.c:2348:\treturn change_page_attr_set_clr(\u0026addr, numpages, __pgprot(0), clr, 0,\narch/x86/mm/pat/set_memory.c-2349-\t\t\t\t\tCPA_COLLAPSE, NULL);\n--\narch/x86/mm/pat/set_memory.c=2362=int set_memory_np_noalias(unsigned long addr, int numpages)\narch/x86/mm/pat/set_memory.c-2363-{\narch/x86/mm/pat/set_memory.c:2364:\treturn change_page_attr_set_clr(\u0026addr, numpages, __pgprot(0),\narch/x86/mm/pat/set_memory.c-2365-\t\t\t\t\t__pgprot(_PAGE_PRESENT), 0,\n--\narch/x86/mm/pat/set_memory.c=2374=int set_memory_4k(unsigned long addr, int numpages)\narch/x86/mm/pat/set_memory.c-2375-{\narch/x86/mm/pat/set_memory.c:2376:\treturn change_page_attr_set_clr(\u0026addr, numpages,\narch/x86/mm/pat/set_memory.c-2377-\t\t\t\t\t__pgprot(_PAGE_KERNEL_4K),\n--\narch/x86/mm/pat/set_memory.c=2397=static int __set_memory_enc_pgtable(unsigned long addr, int numpages, bool enc)\n--\narch/x86/mm/pat/set_memory.c-2426-\narch/x86/mm/pat/set_memory.c:2427:\tret = __change_page_attr_set_clr(\u0026cpa, 1);\narch/x86/mm/pat/set_memory.c-2428-\n--\narch/x86/mm/pat/set_memory.c=2519=static int _set_pages_array(struct page **pages, int numpages,\n--\narch/x86/mm/pat/set_memory.c-2544-\tif (!ret \u0026\u0026 new_type == _PAGE_CACHE_MODE_WC)\narch/x86/mm/pat/set_memory.c:2545:\t\tret = change_page_attr_set_clr(NULL, numpages,\narch/x86/mm/pat/set_memory.c-2546-\t\t\t\t\t       cachemode2pgprot(\n--\narch/x86/mm/pat/set_memory.c=2624=static int __set_pages_p(struct page *page, int numpages)\n--\narch/x86/mm/pat/set_memory.c-2639-\t */\narch/x86/mm/pat/set_memory.c:2640:\treturn __change_page_attr_set_clr(\u0026cpa, 1);\narch/x86/mm/pat/set_memory.c-2641-}\n--\narch/x86/mm/pat/set_memory.c=2643=static int __set_pages_np(struct page *page, int numpages)\n--\narch/x86/mm/pat/set_memory.c-2658-\t */\narch/x86/mm/pat/set_memory.c:2659:\treturn __change_page_attr_set_clr(\u0026cpa, 1);\narch/x86/mm/pat/set_memory.c-2660-}\n--\narch/x86/mm/pat/set_memory.c=2726=int __init kernel_map_pages_in_pgd(pgd_t *pgd, u64 pfn, unsigned long address,\n--\narch/x86/mm/pat/set_memory.c-2750-\narch/x86/mm/pat/set_memory.c:2751:\tretval = __change_page_attr_set_clr(\u0026cpa, 1);\narch/x86/mm/pat/set_memory.c-2752-\t__flush_tlb_all();\n--\narch/x86/mm/pat/set_memory.c=2763=int __init kernel_unmap_pages_in_pgd(pgd_t *pgd, unsigned long address,\n--\narch/x86/mm/pat/set_memory.c-2785-\narch/x86/mm/pat/set_memory.c:2786:\tretval = __change_page_attr_set_clr(\u0026cpa, 1);\narch/x86/mm/pat/set_memory.c-2787-\t__flush_tlb_all();\n"
}

gemini-3.1-pro-preview

null

null

							input: 23147
							output: 21
							thoughts: 158
						

**Analyzing Page Attribute Modification**

Okay, so I'm looking at how page attributes are changed, and the connection is becoming clearer. `change_page_attr_set_clr` is defined as static, which initially makes it seem like it's a locally scoped utility function. However, the fact that it's called by the likes of `set_memory_rox`, `set_memory_4k`, and `set_memory_np_noalias` indicates a wider impact than initially perceived.

On the other hand, `__change_page_attr_set_clr` seems to be used as a core utility function, used across a range of other functions, such as `kernel_map_pages_in_pgd`, `kernel_unmap_pages_in_pgd`, `__set_pages_p`, and `__set_pages_np`. This seems to have a wider scope. Given its role as a fundamental building block for these critical operations, `__change_page_attr_set_clr` seems like a good symbol to focus on. But wait, `change_page_attr_set_clr` is also good.

Alright, let's now check how `walk_page_range_debug` uses it.

{
  "Expression": "walk_page_range_debug"
}

{
  "Output": "Documentation/mm/process_addrs.rst=382=We also permit a truly unusual case is the traversal of non-VMA ranges in\nDocumentation/mm/process_addrs.rst:383:**userland** ranges, as provided for by :c:func:`!walk_page_range_debug`.\nDocumentation/mm/process_addrs.rst-384-\n--\nmm/internal.h=1840=int walk_page_range_vma_unsafe(struct vm_area_struct *vma, unsigned long start,\n--\nmm/internal.h-1842-\t\tvoid *private);\nmm/internal.h:1843:int walk_page_range_debug(struct mm_struct *mm, unsigned long start,\nmm/internal.h-1844-\t\t\t  unsigned long end, const struct mm_walk_ops *ops,\n--\nmm/pagewalk.c=648=int walk_kernel_page_table_range_lockless(unsigned long start, unsigned long end,\n--\nmm/pagewalk.c-667-/**\nmm/pagewalk.c:668: * walk_page_range_debug - walk a range of pagetables not backed by a vma\nmm/pagewalk.c-669- * @mm:\t\tmm_struct representing the target process of page table walk\n--\nmm/pagewalk.c-683- */\nmm/pagewalk.c:684:int walk_page_range_debug(struct mm_struct *mm, unsigned long start,\nmm/pagewalk.c-685-\t\t\t  unsigned long end, const struct mm_walk_ops *ops,\n--\nmm/ptdump.c=175=void ptdump_walk_pgd(struct ptdump_state *st, struct mm_struct *mm, pgd_t *pgd)\n--\nmm/ptdump.c-185-\twhile (range-\u003estart != range-\u003eend) {\nmm/ptdump.c:186:\t\twalk_page_range_debug(mm, range-\u003estart, range-\u003eend,\nmm/ptdump.c-187-\t\t\t\t      \u0026ptdump_ops, pgd, st);\n"
}

gemini-3.1-pro-preview

null

null

							input: 24131
							output: 255
							thoughts: 1486
						

**Analysis of Patch for Kernel Fuzzing**

Okay, so I'm looking at this patch and the first thing that jumps out is that it's touching quite a few areas related to memory management, specifically page table dumping, huge page handling within vmalloc, and the x86 Change Page Attribute (CPA) code. The core change appears to be synchronizing these operations using `init_mm.mmap_lock` instead of the previous static key approach, with additional locking added to the x86 CPA and vmalloc paths. This is a pretty significant change, potentially impacting concurrency and requiring rigorous fuzzing to uncover any subtle race conditions or memory corruption issues.

Let's break this down. The patch introduces changes in three main areas which are prime targets for fuzzing: page table dumping (ptdump), vmalloc huge page setup, and CPA. Since these are all related to page table management and concurrent access, the goal of fuzzing is to expose any potential issues arising from the new locking scheme, possible deadlocks, or use-after-free bugs when concurrent page table walks and modifications happen.

So, `walk_page_range_debug` is exposed in `mm/internal.h` and is called by `ptdump_walk_pgd`. That tells me the symbols that are in scope for fuzzing are:
-   `vmap_try_huge_pmd`, `vmap_try_huge_pud`, `vmap_try_huge_p4d` (dealing with huge pages)
-   `cpa_collapse_large_pages`, `__change_page_attr_set_clr` (CPA code).  Hmm, both `change_page_attr_set_clr` and `__change_page_attr_set_clr` are static, but the patch likely calls them through exported functions like `set_memory_wc` or `set_memory_rox`, so we can still fuzz via those or via CPA_DEBUG.
-   `ptdump_walk_pgd` and `walk_page_range_debug` (page table dumping)
-   `pmd_free_pte_page`, `pud_free_pmd_page`

Okay, let's nail down what configurations are going to be useful for testing this. `PTDUMP_DEBUGFS` seems relevant since it exposes the `ptdump` functionality to debugfs, something syzkaller can easily leverage. `DEBUG_WX` looks useful because it enables `ptdump` at boot. Given that the CPA code is also involved and this patch might make changes to it, `CPA_DEBUG` is a must, since it runs self-tests and will trigger the code. I don't need to specify `DEBUG_FS` because syzkaller usually already has it enabled.

So the configs are:
- `PTDUMP_DEBUGFS`
- `DEBUG_WX`
- `CPA_DEBUG`

I will now verify that the symbol names I'm focusing on are correct, just to be sure. I'll confirm each symbol name. Yep, they all match the definitions in the kernel sources.

I am now ready to provide these details as inputs for setting up the fuzzing environment.

{
  "EnableConfigs": [
    "PTDUMP_DEBUGFS",
    "DEBUG_WX",
    "CPA_DEBUG"
  ],
  "FocusSymbols": [
    "vmap_try_huge_pmd",
    "vmap_try_huge_pud",
    "vmap_try_huge_p4d",
    "cpa_collapse_large_pages",
    "__change_page_attr_set_clr",
    "ptdump_walk_pgd",
    "walk_page_range_debug",
    "pmd_free_pte_page",
    "pud_free_pmd_page"
  ],
  "Reasoning": "The patch modifies page table dumping (ptdump), vmalloc huge page setup, and x86 Change Page Attribute (CPA) code to use `init_mm.mmap_lock` for synchronization. This replaces a static key approach in arm64 and adds locking in x86 CPA and vmalloc. This is a functional change to core memory management and should be fuzzed to ensure no deadlocks or use-after-free issues occur during concurrent page table walks and modifications.",
  "WorthFuzzing": true
}

{
  "EnableConfigs": [
    "PTDUMP_DEBUGFS",
    "DEBUG_WX",
    "CPA_DEBUG"
  ],
  "FocusSymbols": [
    "vmap_try_huge_pmd",
    "vmap_try_huge_pud",
    "vmap_try_huge_p4d",
    "cpa_collapse_large_pages",
    "__change_page_attr_set_clr",
    "ptdump_walk_pgd",
    "walk_page_range_debug",
    "pmd_free_pte_page",
    "pud_free_pmd_page"
  ],
  "Reasoning": "The patch modifies page table dumping (ptdump), vmalloc huge page setup, and x86 Change Page Attribute (CPA) code to use `init_mm.mmap_lock` for synchronization. This replaces a static key approach in arm64 and adds locking in x86 CPA and vmalloc. This is a functional change to core memory management and should be fuzzed to ensure no deadlocks or use-after-free issues occur during concurrent page table walks and modifications.",
  "WorthFuzzing": true
}