AI Trajectory

null

{
  "EnableConfigs": null,
  "FocusSymbols": [],
  "KMSANReasoning": "",
  "NeedsKMSAN": false,
  "Reasoning": "The patch modifies only userspace test harness files in tools/testing/memblock/ to add unit tests for memblock_alloc_low(). It does not affect the compiled kernel image (vmlinux) or kernel modules.",
  "WorthFuzzing": false
}

null

{
  "PatchDiff": "commit c9dcf7db4941aead6a1f8dcd7df7ec4099fe5416\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate:   Mon Sep 7 00:46:51 2026 +0000\n\n    syz-cluster: applied patch under review\n\ndiff --git a/tools/testing/memblock/Makefile b/tools/testing/memblock/Makefile\nindex d80982ccdc209..20524fcbe3c72 100644\n--- a/tools/testing/memblock/Makefile\n+++ b/tools/testing/memblock/Makefile\n@@ -7,7 +7,8 @@ CFLAGS += -I. -I../../include -Wall -O2 -fsanitize=address \\\n LDFLAGS += -fsanitize=address -fsanitize=undefined\n TARGETS = main\n TEST_OFILES = tests/alloc_nid_api.o tests/alloc_helpers_api.o tests/alloc_api.o \\\n-\t\t  tests/basic_api.o tests/common.o tests/alloc_exact_nid_api.o\n+\t\t  tests/basic_api.o tests/common.o tests/alloc_exact_nid_api.o \\\n+\t\t  tests/alloc_low_api.o\n DEP_OFILES = memblock.o lib/slab.o mmzone.o slab.o cmdline.o\n OFILES = main.o $(DEP_OFILES) $(TEST_OFILES)\n EXTR_SRC = ../../../mm/memblock.c\ndiff --git a/tools/testing/memblock/README b/tools/testing/memblock/README\nindex b435f48d8a700..e4fb5f23fb2ea 100644\n--- a/tools/testing/memblock/README\n+++ b/tools/testing/memblock/README\n@@ -67,13 +67,13 @@ memblock\n |-- tests\n |    |-- alloc_api.(c|h)         -- memblock_alloc tests\n |    |-- alloc_helpers_api.(c|h) -- memblock_alloc_from tests\n+|    |-- alloc_low_api.(c|h)     -- memblock_alloc_low tests\n |    |-- alloc_nid_api.(c|h)     -- memblock_alloc_try_nid tests\n |    |-- basic_api.(c|h)         -- memblock_add/memblock_reserve/... tests\n |    |-- common.(c|h)            -- helper functions for resetting memblock;\n |-- main.c        --------------.   dummy physical memory definition\n |-- Makefile                     `- test runner\n |-- README\n-|-- TODO\n |-- .gitignore\n \n Simulating physical memory\n@@ -101,12 +101,11 @@ There's no need to explicitly free the dummy memory from memblock via\n memblock_free() call. The entry will be erased by reset_memblock_regions(),\n called at the beginning of each test.\n \n-Known issues\n-============\n-\n-1. Tests for memblock_alloc_low() can't be easily implemented. The function uses\n-   ARCH_LOW_ADDRESS_LIMIT marco, which can't be changed to point at the low\n-   memory of the memory_block.\n+The simulator defines ARCH_LOW_ADDRESS_LIMIT in asm/dma.h using the midpoint\n+of the MEM_SIZE range beginning at the dummy physical memory base. This keeps\n+the low-address limit within the allocated buffer even when malloc() returns\n+an address above the kernel's default limit. The limit is an exclusive upper\n+bound, as in the memblock allocation API.\n \n References\n ==========\ndiff --git a/tools/testing/memblock/TODO b/tools/testing/memblock/TODO\ndeleted file mode 100644\nindex c13ad0dae7763..0000000000000\n--- a/tools/testing/memblock/TODO\n+++ /dev/null\n@@ -1,5 +0,0 @@\n-TODO\n-=====\n-\n-1. Add tests for memblock_alloc_low() once the simulator can model\n-   ARCH_LOW_ADDRESS_LIMIT against the low memory in memory_block\ndiff --git a/tools/testing/memblock/asm/dma.h b/tools/testing/memblock/asm/dma.h\nindex 13ff8e5d22ef6..6607408dcf25d 100644\n--- a/tools/testing/memblock/asm/dma.h\n+++ b/tools/testing/memblock/asm/dma.h\n@@ -2,4 +2,10 @@\n #ifndef _TOOLS_DMA_H\n #define _TOOLS_DMA_H\n \n+#include \u003clinux/types.h\u003e\n+\n+phys_addr_t dummy_physical_memory_low_limit(void);\n+\n+#define ARCH_LOW_ADDRESS_LIMIT dummy_physical_memory_low_limit()\n+\n #endif\ndiff --git a/tools/testing/memblock/main.c b/tools/testing/memblock/main.c\nindex 278f9dec50087..9a96e178551b8 100644\n--- a/tools/testing/memblock/main.c\n+++ b/tools/testing/memblock/main.c\n@@ -4,6 +4,7 @@\n #include \"tests/alloc_helpers_api.h\"\n #include \"tests/alloc_nid_api.h\"\n #include \"tests/alloc_exact_nid_api.h\"\n+#include \"tests/alloc_low_api.h\"\n #include \"tests/common.h\"\n \n int main(int argc, char **argv)\n@@ -12,6 +13,7 @@ int main(int argc, char **argv)\n \tmemblock_basic_checks();\n \tmemblock_alloc_checks();\n \tmemblock_alloc_helpers_checks();\n+\tmemblock_alloc_low_checks();\n \tmemblock_alloc_nid_checks();\n \tmemblock_alloc_exact_nid_checks();\n \ndiff --git a/tools/testing/memblock/tests/alloc_low_api.c b/tools/testing/memblock/tests/alloc_low_api.c\nnew file mode 100644\nindex 0000000000000..a0fae975a26bc\n--- /dev/null\n+++ b/tools/testing/memblock/tests/alloc_low_api.c\n@@ -0,0 +1,147 @@\n+// SPDX-License-Identifier: GPL-2.0-or-later\n+#include \"alloc_low_api.h\"\n+#include \u003clinux/align.h\u003e\n+\n+/* Allocate at the first or last aligned address below the low limit. */\n+static int alloc_low_simple_check(void)\n+{\n+\tstruct memblock_region *rgn = \u0026memblock.reserved.regions[0];\n+\tphys_addr_t size = SZ_64;\n+\tphys_addr_t expected;\n+\tvoid *allocated_ptr;\n+\n+\tPREFIX_PUSH();\n+\tsetup_memblock();\n+\n+\tif (memblock_bottom_up())\n+\t\texpected = ALIGN(memblock_start_of_DRAM(), SMP_CACHE_BYTES);\n+\telse\n+\t\texpected = ALIGN_DOWN(ARCH_LOW_ADDRESS_LIMIT - size,\n+\t\t\t\t      SMP_CACHE_BYTES);\n+\n+\tallocated_ptr = memblock_alloc_low(size, SMP_CACHE_BYTES);\n+\n+\tASSERT_NE(allocated_ptr, NULL);\n+\tASSERT_EQ((phys_addr_t)(uintptr_t)allocated_ptr, expected);\n+\tASSERT_MEM_EQ(allocated_ptr, 0, size);\n+\tASSERT_EQ(rgn-\u003ebase, expected);\n+\tASSERT_EQ(rgn-\u003esize, size);\n+\tASSERT_LE(region_end(rgn), ARCH_LOW_ADDRESS_LIMIT);\n+\tASSERT_EQ(memblock.reserved.cnt, 1);\n+\tASSERT_EQ(memblock.reserved.total_size, size);\n+\n+\ttest_pass_pop();\n+\treturn 0;\n+}\n+\n+/* The only low memory available ends exactly at the exclusive limit. */\n+static int alloc_low_exact_limit_check(void)\n+{\n+\tphys_addr_t limit = ARCH_LOW_ADDRESS_LIMIT;\n+\tphys_addr_t base = ALIGN_DOWN(limit - SZ_64, SMP_CACHE_BYTES);\n+\tphys_addr_t size = limit - base;\n+\tvoid *allocated_ptr;\n+\n+\tPREFIX_PUSH();\n+\tsetup_memblock();\n+\tASSERT_EQ(memblock_remove(memblock_start_of_DRAM(),\n+\t\t\t\t  base - memblock_start_of_DRAM()), 0);\n+\n+\tallocated_ptr = memblock_alloc_low(size, SMP_CACHE_BYTES);\n+\n+\tASSERT_NE(allocated_ptr, NULL);\n+\tASSERT_EQ((phys_addr_t)(uintptr_t)allocated_ptr, base);\n+\tASSERT_MEM_EQ(allocated_ptr, 0, size);\n+\tASSERT_EQ(memblock.reserved.regions[0].base, base);\n+\tASSERT_EQ(region_end(\u0026memblock.reserved.regions[0]), limit);\n+\tASSERT_EQ(memblock.reserved.cnt, 1);\n+\tASSERT_EQ(memblock.reserved.total_size, size);\n+\n+\ttest_pass_pop();\n+\treturn 0;\n+}\n+\n+/*\n+ * There are size bytes below the limit, but aligning the start makes the\n+ * allocation cross it. Memory above the limit must not satisfy the request.\n+ */\n+static int alloc_low_alignment_crosses_limit_check(void)\n+{\n+\tphys_addr_t limit = ARCH_LOW_ADDRESS_LIMIT;\n+\tphys_addr_t base = ALIGN_DOWN(limit, SMP_CACHE_BYTES) - 1;\n+\tphys_addr_t size = limit - base;\n+\tvoid *allocated_ptr;\n+\n+\tPREFIX_PUSH();\n+\tsetup_memblock();\n+\tASSERT_EQ(memblock_remove(memblock_start_of_DRAM(),\n+\t\t\t\t  base - memblock_start_of_DRAM()), 0);\n+\n+\tallocated_ptr = memblock_alloc_low(size, SMP_CACHE_BYTES);\n+\n+\tASSERT_EQ(allocated_ptr, NULL);\n+\tASSERT_EQ(memblock.reserved.cnt, 0);\n+\tASSERT_EQ(memblock.reserved.total_size, 0);\n+\tASSERT_MEM_EQ((void *)(uintptr_t)base, 1, memblock_end_of_DRAM() - base);\n+\n+\ttest_pass_pop();\n+\treturn 0;\n+}\n+\n+/* Reserving all low memory must fail even though high memory remains free. */\n+static int alloc_low_reserved_check(void)\n+{\n+\tphys_addr_t limit = ARCH_LOW_ADDRESS_LIMIT;\n+\tphys_addr_t base = dummy_physical_memory_base();\n+\tphys_addr_t size = SZ_64;\n+\tvoid *allocated_ptr;\n+\n+\tPREFIX_PUSH();\n+\tsetup_memblock();\n+\tASSERT_EQ(memblock_reserve(base, limit - base), 0);\n+\n+\tallocated_ptr = memblock_alloc_low(size, SMP_CACHE_BYTES);\n+\n+\tASSERT_EQ(allocated_ptr, NULL);\n+\tASSERT_EQ(memblock.reserved.cnt, 1);\n+\tASSERT_EQ(memblock.reserved.regions[0].base, base);\n+\tASSERT_EQ(memblock.reserved.regions[0].size, limit - base);\n+\tASSERT_EQ(memblock.reserved.total_size, limit - base);\n+\tASSERT_MEM_EQ((void *)(uintptr_t)base, 1, MEM_SIZE);\n+\n+\tallocated_ptr = memblock_alloc(size, SMP_CACHE_BYTES);\n+\tASSERT_NE(allocated_ptr, NULL);\n+\tASSERT_LE(limit, (phys_addr_t)(uintptr_t)allocated_ptr);\n+\tASSERT_MEM_EQ(allocated_ptr, 0, size);\n+\n+\ttest_pass_pop();\n+\treturn 0;\n+}\n+\n+static int alloc_low_checks(void)\n+{\n+\talloc_low_simple_check();\n+\talloc_low_exact_limit_check();\n+\talloc_low_alignment_crosses_limit_check();\n+\talloc_low_reserved_check();\n+\n+\treturn 0;\n+}\n+\n+int memblock_alloc_low_checks(void)\n+{\n+\tprefix_reset();\n+\tprefix_push(\"memblock_alloc_low\");\n+\ttest_print(\"Running memblock_alloc_low tests...\\n\");\n+\n+\treset_memblock_attributes();\n+\tdummy_physical_memory_init();\n+\n+\trun_top_down(alloc_low_checks);\n+\trun_bottom_up(alloc_low_checks);\n+\n+\tdummy_physical_memory_cleanup();\n+\tprefix_pop();\n+\n+\treturn 0;\n+}\ndiff --git a/tools/testing/memblock/tests/alloc_low_api.h b/tools/testing/memblock/tests/alloc_low_api.h\nnew file mode 100644\nindex 0000000000000..2e3cbe336f5da\n--- /dev/null\n+++ b/tools/testing/memblock/tests/alloc_low_api.h\n@@ -0,0 +1,9 @@\n+/* SPDX-License-Identifier: GPL-2.0-or-later */\n+#ifndef _MEMBLOCK_ALLOC_LOW_H\n+#define _MEMBLOCK_ALLOC_LOW_H\n+\n+#include \"common.h\"\n+\n+int memblock_alloc_low_checks(void);\n+\n+#endif\ndiff --git a/tools/testing/memblock/tests/common.c b/tools/testing/memblock/tests/common.c\nindex 3250c8e5124b3..4e6a920c459e9 100644\n--- a/tools/testing/memblock/tests/common.c\n+++ b/tools/testing/memblock/tests/common.c\n@@ -118,6 +118,11 @@ phys_addr_t dummy_physical_memory_base(void)\n \treturn (phys_addr_t)memory_block.base;\n }\n \n+phys_addr_t dummy_physical_memory_low_limit(void)\n+{\n+\treturn dummy_physical_memory_base() + MEM_SIZE / 2;\n+}\n+\n static void usage(const char *prog)\n {\n \tBUILD_BUG_ON(ARRAY_SIZE(help_opts) != ARRAY_SIZE(long_opts) - 1);\n"
}

core

null

{
  "EnableConfigs": null,
  "FocusSymbols": [],
  "Reasoning": "The patch modifies only userspace test harness files in tools/testing/memblock/ to add unit tests for memblock_alloc_low(). It does not affect the compiled kernel image (vmlinux) or kernel modules.",
  "WorthFuzzing": false
}

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.

Target architecture: amd64

For your convenience, here is the diff of the changes:
commit c9dcf7db4941aead6a1f8dcd7df7ec4099fe5416
Author: syz-cluster <triage@syzkaller.com>
Date:   Mon Sep 7 00:46:51 2026 +0000

    syz-cluster: applied patch under review

diff --git a/tools/testing/memblock/Makefile b/tools/testing/memblock/Makefile
index d80982ccdc209..20524fcbe3c72 100644
--- a/tools/testing/memblock/Makefile
+++ b/tools/testing/memblock/Makefile
@@ -7,7 +7,8 @@ CFLAGS += -I. -I../../include -Wall -O2 -fsanitize=address \
 LDFLAGS += -fsanitize=address -fsanitize=undefined
 TARGETS = main
 TEST_OFILES = tests/alloc_nid_api.o tests/alloc_helpers_api.o tests/alloc_api.o \
-		  tests/basic_api.o tests/common.o tests/alloc_exact_nid_api.o
+		  tests/basic_api.o tests/common.o tests/alloc_exact_nid_api.o \
+		  tests/alloc_low_api.o
 DEP_OFILES = memblock.o lib/slab.o mmzone.o slab.o cmdline.o
 OFILES = main.o $(DEP_OFILES) $(TEST_OFILES)
 EXTR_SRC = ../../../mm/memblock.c
diff --git a/tools/testing/memblock/README b/tools/testing/memblock/README
index b435f48d8a700..e4fb5f23fb2ea 100644
--- a/tools/testing/memblock/README
+++ b/tools/testing/memblock/README
@@ -67,13 +67,13 @@ memblock
 |-- tests
 |    |-- alloc_api.(c|h)         -- memblock_alloc tests
 |    |-- alloc_helpers_api.(c|h) -- memblock_alloc_from tests
+|    |-- alloc_low_api.(c|h)     -- memblock_alloc_low tests
 |    |-- alloc_nid_api.(c|h)     -- memblock_alloc_try_nid tests
 |    |-- basic_api.(c|h)         -- memblock_add/memblock_reserve/... tests
 |    |-- common.(c|h)            -- helper functions for resetting memblock;
 |-- main.c        --------------.   dummy physical memory definition
 |-- Makefile                     `- test runner
 |-- README
-|-- TODO
 |-- .gitignore
 
 Simulating physical memory
@@ -101,12 +101,11 @@ There's no need to explicitly free the dummy memory from memblock via
 memblock_free() call. The entry will be erased by reset_memblock_regions(),
 called at the beginning of each test.
 
-Known issues
-============
-
-1. Tests for memblock_alloc_low() can't be easily implemented. The function uses
-   ARCH_LOW_ADDRESS_LIMIT marco, which can't be changed to point at the low
-   memory of the memory_block.
+The simulator defines ARCH_LOW_ADDRESS_LIMIT in asm/dma.h using the midpoint
+of the MEM_SIZE range beginning at the dummy physical memory base. This keeps
+the low-address limit within the allocated buffer even when malloc() returns
+an address above the kernel's default limit. The limit is an exclusive upper
+bound, as in the memblock allocation API.
 
 References
 ==========
diff --git a/tools/testing/memblock/TODO b/tools/testing/memblock/TODO
deleted file mode 100644
index c13ad0dae7763..0000000000000
--- a/tools/testing/memblock/TODO
+++ /dev/null
@@ -1,5 +0,0 @@
-TODO
-=====
-
-1. Add tests for memblock_alloc_low() once the simulator can model
-   ARCH_LOW_ADDRESS_LIMIT against the low memory in memory_block
diff --git a/tools/testing/memblock/asm/dma.h b/tools/testing/memblock/asm/dma.h
index 13ff8e5d22ef6..6607408dcf25d 100644
--- a/tools/testing/memblock/asm/dma.h
+++ b/tools/testing/memblock/asm/dma.h
@@ -2,4 +2,10 @@
 #ifndef _TOOLS_DMA_H
 #define _TOOLS_DMA_H
 
+#include <linux/types.h>
+
+phys_addr_t dummy_physical_memory_low_limit(void);
+
+#define ARCH_LOW_ADDRESS_LIMIT dummy_physical_memory_low_limit()
+
 #endif
diff --git a/tools/testing/memblock/main.c b/tools/testing/memblock/main.c
index 278f9dec50087..9a96e178551b8 100644
--- a/tools/testing/memblock/main.c
+++ b/tools/testing/memblock/main.c
@@ -4,6 +4,7 @@
 #include "tests/alloc_helpers_api.h"
 #include "tests/alloc_nid_api.h"
 #include "tests/alloc_exact_nid_api.h"
+#include "tests/alloc_low_api.h"
 #include "tests/common.h"
 
 int main(int argc, char **argv)
@@ -12,6 +13,7 @@ int main(int argc, char **argv)
 	memblock_basic_checks();
 	memblock_alloc_checks();
 	memblock_alloc_helpers_checks();
+	memblock_alloc_low_checks();
 	memblock_alloc_nid_checks();
 	memblock_alloc_exact_nid_checks();
 
diff --git a/tools/testing/memblock/tests/alloc_low_api.c b/tools/testing/memblock/tests/alloc_low_api.c
new file mode 100644
index 0000000000000..a0fae975a26bc
--- /dev/null
+++ b/tools/testing/memblock/tests/alloc_low_api.c
@@ -0,0 +1,147 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+#include "alloc_low_api.h"
+#include <linux/align.h>
+
+/* Allocate at the first or last aligned address below the low limit. */
+static int alloc_low_simple_check(void)
+{
+	struct memblock_region *rgn = &memblock.reserved.regions[0];
+	phys_addr_t size = SZ_64;
+	phys_addr_t expected;
+	void *allocated_ptr;
+
+	PREFIX_PUSH();
+	setup_memblock();
+
+	if (memblock_bottom_up())
+		expected = ALIGN(memblock_start_of_DRAM(), SMP_CACHE_BYTES);
+	else
+		expected = ALIGN_DOWN(ARCH_LOW_ADDRESS_LIMIT - size,
+				      SMP_CACHE_BYTES);
+
+	allocated_ptr = memblock_alloc_low(size, SMP_CACHE_BYTES);
+
+	ASSERT_NE(allocated_ptr, NULL);
+	ASSERT_EQ((phys_addr_t)(uintptr_t)allocated_ptr, expected);
+	ASSERT_MEM_EQ(allocated_ptr, 0, size);
+	ASSERT_EQ(rgn->base, expected);
+	ASSERT_EQ(rgn->size, size);
+	ASSERT_LE(region_end(rgn), ARCH_LOW_ADDRESS_LIMIT);
+	ASSERT_EQ(memblock.reserved.cnt, 1);
+	ASSERT_EQ(memblock.reserved.total_size, size);
+
+	test_pass_pop();
+	return 0;
+}
+
+/* The only low memory available ends exactly at the exclusive limit. */
+static int alloc_low_exact_limit_check(void)
+{
+	phys_addr_t limit = ARCH_LOW_ADDRESS_LIMIT;
+	phys_addr_t base = ALIGN_DOWN(limit - SZ_64, SMP_CACHE_BYTES);
+	phys_addr_t size = limit - base;
+	void *allocated_ptr;
+
+	PREFIX_PUSH();
+	setup_memblock();
+	ASSERT_EQ(memblock_remove(memblock_start_of_DRAM(),
+				  base - memblock_start_of_DRAM()), 0);
+
+	allocated_ptr = memblock_alloc_low(size, SMP_CACHE_BYTES);
+
+	ASSERT_NE(allocated_ptr, NULL);
+	ASSERT_EQ((phys_addr_t)(uintptr_t)allocated_ptr, base);
+	ASSERT_MEM_EQ(allocated_ptr, 0, size);
+	ASSERT_EQ(memblock.reserved.regions[0].base, base);
+	ASSERT_EQ(region_end(&memblock.reserved.regions[0]), limit);
+	ASSERT_EQ(memblock.reserved.cnt, 1);
+	ASSERT_EQ(memblock.reserved.total_size, size);
+
+	test_pass_pop();
+	return 0;
+}
+
+/*
+ * There are size bytes below the limit, but aligning the start makes the
+ * allocation cross it. Memory above the limit must not satisfy the request.
+ */
+static int alloc_low_alignment_crosses_limit_check(void)
+{
+	phys_addr_t limit = ARCH_LOW_ADDRESS_LIMIT;
+	phys_addr_t base = ALIGN_DOWN(limit, SMP_CACHE_BYTES) - 1;
+	phys_addr_t size = limit - base;
+	void *allocated_ptr;
+
+	PREFIX_PUSH();
+	setup_memblock();
+	ASSERT_EQ(memblock_remove(memblock_start_of_DRAM(),
+				  base - memblock_start_of_DRAM()), 0);
+
+	allocated_ptr = memblock_alloc_low(size, SMP_CACHE_BYTES);
+
+	ASSERT_EQ(allocated_ptr, NULL);
+	ASSERT_EQ(memblock.reserved.cnt, 0);
+	ASSERT_EQ(memblock.reserved.total_size, 0);
+	ASSERT_MEM_EQ((void *)(uintptr_t)base, 1, memblock_end_of_DRAM() - base);
+
+	test_pass_pop();
+	return 0;
+}
+
+/* Reserving all low memory must fail even though high memory remains free. */
+static int alloc_low_reserved_check(void)
+{
+	phys_addr_t limit = ARCH_LOW_ADDRESS_LIMIT;
+	phys_addr_t base = dummy_physical_memory_base();
+	phys_addr_t size = SZ_64;
+	void *allocated_ptr;
+
+	PREFIX_PUSH();
+	setup_memblock();
+	ASSERT_EQ(memblock_reserve(base, limit - base), 0);
+
+	allocated_ptr = memblock_alloc_low(size, SMP_CACHE_BYTES);
+
+	ASSERT_EQ(allocated_ptr, NULL);
+	ASSERT_EQ(memblock.reserved.cnt, 1);
+	ASSERT_EQ(memblock.reserved.regions[0].base, base);
+	ASSERT_EQ(memblock.reserved.regions[0].size, limit - base);
+	ASSERT_EQ(memblock.reserved.total_size, limit - base);
+	ASSERT_MEM_EQ((void *)(uintptr_t)base, 1, MEM_SIZE);
+
+	allocated_ptr = memblock_alloc(size, SMP_CACHE_BYTES);
+	ASSERT_NE(allocated_ptr, NULL);
+	ASSERT_LE(limit, (phys_addr_t)(uintptr_t)allocated_ptr);
+	ASSERT_MEM_EQ(allocated_ptr, 0, size);
+
+	test_pass_pop();
+	return 0;
+}
+
+static int alloc_low_checks(void)
+{
+	alloc_low_simple_check();
+	alloc_low_exact_limit_check();
+	alloc_low_alignment_crosses_limit_check();
+	alloc_low_reserved_check();
+
+	return 0;
+}
+
+int memblock_alloc_low_checks(void)
+{
+	prefix_reset();
+	prefix_push("memblock_alloc_low");
+	test_print("Running memblock_alloc_low tests...\n");
+
+	reset_memblock_attributes();
+	dummy_physical_memory_init();
+
+	run_top_down(alloc_low_checks);
+	run_bottom_up(alloc_low_checks);
+
+	dummy_physical_memory_cleanup();
+	prefix_pop();
+
+	return 0;
+}
diff --git a/tools/testing/memblock/tests/alloc_low_api.h b/tools/testing/memblock/tests/alloc_low_api.h
new file mode 100644
index 0000000000000..2e3cbe336f5da
--- /dev/null
+++ b/tools/testing/memblock/tests/alloc_low_api.h
@@ -0,0 +1,9 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef _MEMBLOCK_ALLOC_LOW_H
+#define _MEMBLOCK_ALLOC_LOW_H
+
+#include "common.h"
+
+int memblock_alloc_low_checks(void);
+
+#endif
diff --git a/tools/testing/memblock/tests/common.c b/tools/testing/memblock/tests/common.c
index 3250c8e5124b3..4e6a920c459e9 100644
--- a/tools/testing/memblock/tests/common.c
+++ b/tools/testing/memblock/tests/common.c
@@ -118,6 +118,11 @@ phys_addr_t dummy_physical_memory_base(void)
 	return (phys_addr_t)memory_block.base;
 }
 
+phys_addr_t dummy_physical_memory_low_limit(void)
+{
+	return dummy_physical_memory_base() + MEM_SIZE / 2;
+}
+
 static void usage(const char *prog)
 {
 	BUILD_BUG_ON(ARRAY_SIZE(help_opts) != ARRAY_SIZE(long_opts) - 1);

gemini-3.7-flash

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							input: 6263
							output: 23
							thoughts: 373
						

**Evaluating the Patch for Syzkaller Fuzzing**

Okay, so the task at hand is to determine if this patch justifies fuzzing with syzkaller. My initial step is to dive into the patch diff and see what's changed. Based on the files modified, it looks like this patch is entirely contained within `tools/testing/memblock/`. Specifically, I see changes to the `Makefile`, `README`, `TODO`, and `asm/dma.h`, `main.c`, and several test files.

Now, let's apply my expertise to the guidelines. Referring to the "WHEN TO RETURN WorthFuzzing=false" section, the criteria for *not* fuzzing seem pretty clear-cut. The relevant rule states that if all changes are confined to non-kernel, non-executable areas such as documentation, user-space tools, self-tests, or scripts that *don't* impact the kernel image (`vmlinux`) or modules, then we shouldn't recommend fuzzing.

Given that these modifications are exclusively within the `tools/testing/memblock/` directory, which I recognize as user-space test code, it clearly falls into that category. It's essentially self-tests that don't affect the compiled kernel.

Just to be absolutely certain, I'll quickly double-check that this is indeed the full scope of the change. I'll inspect the commit or tree details, and I might even run a quick tool check, just to be 100% sure we aren't missing any hidden modifications outside of the `tools/` directory. But based on the initial assessment, the answer is clear: this patch doesn't warrant fuzzing with syzkaller.

{
  "Expression": "dummy_physical_memory_low_limit"
}

{
  "Output": "tools/testing/memblock/asm/dma.h-6-\ntools/testing/memblock/asm/dma.h:7:phys_addr_t dummy_physical_memory_low_limit(void);\ntools/testing/memblock/asm/dma.h-8-\ntools/testing/memblock/asm/dma.h:9:#define ARCH_LOW_ADDRESS_LIMIT dummy_physical_memory_low_limit()\ntools/testing/memblock/asm/dma.h-10-\n--\ntools/testing/memblock/tests/common.c=116=phys_addr_t dummy_physical_memory_base(void)\n--\ntools/testing/memblock/tests/common.c-120-\ntools/testing/memblock/tests/common.c:121:phys_addr_t dummy_physical_memory_low_limit(void)\ntools/testing/memblock/tests/common.c-122-{\n"
}

gemini-3.7-flash

null

null

							input: 7264
							output: 77
							thoughts: 94
						

Okay, here's my take on that patch, distilled to its core reasoning:

**Patch Analysis and Fuzzing Prioritization**

Right, so this patch is laser-focused on the `tools/testing/memblock/` directory. That's immediately telling. It's user-space test code, specifically for the `memblock_alloc_low` function. Given that, the implications are pretty clear.

*   `WorthFuzzing` has to be `false`. This isn't touching kernel internals that would be the targets of fuzzing. No kernel image (vmlinux) or kernel module compilation is affected.
*   `EnableConfigs`? Empty list, no doubt. The changes here won't necessitate enabling any specific kernel configuration options. This is purely user-space testing and validation.
*   `FocusSymbols`? Again, an empty list. We're not looking to fuzz or analyze any kernel symbols directly with these changes. The `memblock_alloc_low` function being tested here is the focus and will be tested via these tests in that location.

So, in essence, this is a very contained patch. It's adding and modifying some user-space tests, nothing more, nothing less. I'll flag that and then call `set-results`.

{
  "EnableConfigs": [],
  "FocusSymbols": [],
  "Reasoning": "The patch modifies only userspace test harness files in tools/testing/memblock/ to add unit tests for memblock_alloc_low(). It does not affect the compiled kernel image (vmlinux) or kernel modules.",
  "WorthFuzzing": false
}

{
  "EnableConfigs": null,
  "FocusSymbols": [],
  "Reasoning": "The patch modifies only userspace test harness files in tools/testing/memblock/ to add unit tests for memblock_alloc_low(). It does not affect the compiled kernel image (vmlinux) or kernel modules.",
  "WorthFuzzing": false
}

{
  "WorthFuzzing": false
}

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