AI Trajectory

null

{
  "EnableConfigs": null,
  "FocusSymbols": [],
  "Reasoning": "The patch introduces new APIs (`kho_preserve_page`, `kho_unpreserve_page`, `kho_restore_page`) for Kexec Handover (KHO) which are currently unused anywhere in the kernel tree. It also refactors `kho_restore_folio` and `kho_restore_pages` to use a new internal helper `__kho_restore_page`, and modifies `kho_init_high_order_page` to clear page tags for tail pages. However, all of these modified code paths are only reachable during the KHO restore phase, which strictly requires the kernel to be booted with KHO data passed from a previous kernel. Since syzkaller boots from a fresh VM image without KHO data, this code is completely unreachable in a standard fuzzing environment.",
  "WorthFuzzing": false
}

null

{
  "PatchDiff": "commit c8d66e8c1c74d3d08640eb0a8fd77ed6b728885e\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate:   Mon Aug 3 17:06:32 2026 +0000\n\n    syz-cluster: applied patch under review\n\ndiff --git a/include/linux/kexec_handover.h b/include/linux/kexec_handover.h\nindex 8968c56d2d73e..6e2c75b16209c 100644\n--- a/include/linux/kexec_handover.h\n+++ b/include/linux/kexec_handover.h\n@@ -22,6 +22,8 @@ bool is_kho_boot(void);\n \n int kho_preserve_folio(struct folio *folio);\n void kho_unpreserve_folio(struct folio *folio);\n+int kho_preserve_page(struct page *page, unsigned int order);\n+void kho_unpreserve_page(struct page *page, unsigned int order);\n int kho_preserve_pages(struct page *page, unsigned long nr_pages);\n void kho_unpreserve_pages(struct page *page, unsigned long nr_pages);\n int kho_preserve_vmalloc(void *ptr, struct kho_vmalloc *preservation);\n@@ -30,6 +32,7 @@ void *kho_alloc_preserve(size_t size);\n void kho_unpreserve_free(void *mem);\n void kho_restore_free(void *mem);\n struct folio *kho_restore_folio(phys_addr_t phys);\n+struct page *kho_restore_page(phys_addr_t phys);\n struct page *kho_restore_pages(phys_addr_t phys, unsigned long nr_pages);\n void *kho_restore_vmalloc(const struct kho_vmalloc *preservation);\n int kho_add_subtree(const char *name, void *blob, size_t size);\n@@ -65,6 +68,13 @@ static inline int kho_preserve_pages(struct page *page, unsigned int nr_pages)\n \n static inline void kho_unpreserve_pages(struct page *page, unsigned int nr_pages) { }\n \n+static inline int kho_preserve_page(struct page *page, unsigned int order)\n+{\n+\treturn -EOPNOTSUPP;\n+}\n+\n+static inline void kho_unpreserve_page(struct page *page, unsigned int order) { }\n+\n static inline int kho_preserve_vmalloc(void *ptr,\n \t\t\t\t       struct kho_vmalloc *preservation)\n {\ndiff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c\nindex 4834a809985ab..dd41d324c213d 100644\n--- a/kernel/liveupdate/kexec_handover.c\n+++ b/kernel/liveupdate/kexec_handover.c\n@@ -357,6 +357,24 @@ int kho_radix_walk_tree(struct kho_radix_tree *tree,\n }\n EXPORT_SYMBOL_GPL(kho_radix_walk_tree);\n \n+/* For physically contiguous pages. */\n+static void kho_init_high_order_page(struct page *page, unsigned int order)\n+{\n+\tunsigned long nr_pages = (1UL \u003c\u003c order);\n+\n+\t/* Head page gets refcount of 1. */\n+\tset_page_count(page, 1);\n+\t/* Clear head page's codetag to avoid accounting mismatch. */\n+\tclear_page_tag_ref(page);\n+\n+\t/* For high-order blocks, tail pages get a page count of zero. */\n+\tfor (unsigned long i = 1; i \u003c nr_pages; i++) {\n+\t\tset_page_count(page + i, 0);\n+\t\t/* Clear each page's codetag to avoid accounting mismatch. */\n+\t\tclear_page_tag_ref(page + i);\n+\t}\n+}\n+\n /* For physically contiguous 0-order pages. */\n static void kho_init_pages(struct page *page, unsigned long nr_pages)\n {\n@@ -369,25 +387,15 @@ static void kho_init_pages(struct page *page, unsigned long nr_pages)\n \n static void kho_init_folio(struct page *page, unsigned int order)\n {\n-\tunsigned long nr_pages = (1 \u003c\u003c order);\n-\n-\t/* Head page gets refcount of 1. */\n-\tset_page_count(page, 1);\n-\t/* Clear head page's codetag to avoid accounting mismatch. */\n-\tclear_page_tag_ref(page);\n-\n-\t/* For higher order folios, tail pages get a page count of zero. */\n-\tfor (unsigned long i = 1; i \u003c nr_pages; i++)\n-\t\tset_page_count(page + i, 0);\n+\tkho_init_high_order_page(page, order);\n \n \tif (order \u003e 0)\n \t\tprep_compound_page(page, order);\n }\n \n-static struct page *kho_restore_page(phys_addr_t phys, bool is_folio)\n+static struct page *__kho_restore_page(phys_addr_t phys, unsigned int *order)\n {\n \tstruct page *page = pfn_to_online_page(PHYS_PFN(phys));\n-\tunsigned long nr_pages;\n \tunion kho_page_info info;\n \n \tif (!page)\n@@ -401,17 +409,14 @@ static struct page *kho_restore_page(phys_addr_t phys, bool is_folio)\n \t */\n \tif (WARN_ON_ONCE(info.magic != KHO_PAGE_MAGIC))\n \t\treturn NULL;\n-\tnr_pages = (1 \u003c\u003c info.order);\n \n \t/* Clear private to make sure later restores on this page error out. */\n \tpage-\u003eprivate = 0;\n+\tif (order)\n+\t\t*order = info.order;\n \n-\tif (is_folio)\n-\t\tkho_init_folio(page, info.order);\n-\telse\n-\t\tkho_init_pages(page, nr_pages);\n+\tadjust_managed_page_count(page, 1UL \u003c\u003c info.order);\n \n-\tadjust_managed_page_count(page, nr_pages);\n \treturn page;\n }\n \n@@ -423,12 +428,41 @@ static struct page *kho_restore_page(phys_addr_t phys, bool is_folio)\n  */\n struct folio *kho_restore_folio(phys_addr_t phys)\n {\n-\tstruct page *page = kho_restore_page(phys, true);\n+\tunsigned int order;\n+\tstruct page *page = __kho_restore_page(phys, \u0026order);\n+\n+\tif (!page)\n+\t\treturn NULL;\n+\n+\tkho_init_folio(page, order);\n \n-\treturn page ? page_folio(page) : NULL;\n+\treturn page_folio(page);\n }\n EXPORT_SYMBOL_GPL(kho_restore_folio);\n \n+/**\n+ * kho_restore_page - restore a high-order page block.\n+ * @phys: physical address of the first page.\n+ *\n+ * Restore a high-order page block that was preserved with\n+ * kho_preserve_page().\n+ *\n+ * Return: the head page on success, NULL on failure.\n+ */\n+struct page *kho_restore_page(phys_addr_t phys)\n+{\n+\tunsigned int order;\n+\tstruct page *page = __kho_restore_page(phys, \u0026order);\n+\n+\tif (!page)\n+\t\treturn NULL;\n+\n+\tkho_init_high_order_page(page, order);\n+\n+\treturn page;\n+}\n+EXPORT_SYMBOL_GPL(kho_restore_page);\n+\n /**\n  * kho_restore_pages - restore list of contiguous order 0 pages.\n  * @phys: physical address of the first page.\n@@ -448,10 +482,13 @@ struct page *kho_restore_pages(phys_addr_t phys, unsigned long nr_pages)\n \twhile (pfn \u003c end_pfn) {\n \t\tconst unsigned int order =\n \t\t\tmin(count_trailing_zeros(pfn), ilog2(end_pfn - pfn));\n-\t\tstruct page *page = kho_restore_page(PFN_PHYS(pfn), false);\n+\t\tunsigned int info_order;\n+\t\tstruct page *page = __kho_restore_page(PFN_PHYS(pfn), \u0026info_order);\n \n \t\tif (!page)\n \t\t\treturn NULL;\n+\n+\t\tkho_init_pages(page, 1UL \u003c\u003c info_order);\n \t\tpfn += 1 \u003c\u003c order;\n \t}\n \n@@ -881,6 +918,51 @@ void kho_unpreserve_folio(struct folio *folio)\n }\n EXPORT_SYMBOL_GPL(kho_unpreserve_folio);\n \n+/**\n+ * kho_preserve_page - preserve a high-order page block.\n+ * @page: head page of the block.\n+ * @order: order of the allocation.\n+ *\n+ * Instructs KHO to preserve a high-order contiguous allocation (like a DMA\n+ * buffer) as a single unit. It must be restored using kho_restore_page() to\n+ * ensure the tail pages are correctly initialized with a zero refcount.\n+ *\n+ * If a driver needs to split a block that has been preserved with this\n+ * function, it must first unpreserve the block using kho_unpreserve_page(),\n+ * perform the split, and then re-preserve the individual pages using\n+ * kho_preserve_pages().\n+ *\n+ * Return: 0 on success, error code on failure\n+ */\n+int kho_preserve_page(struct page *page, unsigned int order)\n+{\n+\tstruct kho_radix_tree *tree = \u0026kho_out.radix_tree;\n+\tconst unsigned long pfn = page_to_pfn(page);\n+\n+\tif (WARN_ON(kho_scratch_overlap(pfn \u003c\u003c PAGE_SHIFT, PAGE_SIZE \u003c\u003c order)))\n+\t\treturn -EINVAL;\n+\n+\treturn kho_radix_add_page(tree, pfn, order);\n+}\n+EXPORT_SYMBOL_GPL(kho_preserve_page);\n+\n+/**\n+ * kho_unpreserve_page - unpreserve a high-order page block.\n+ * @page: head page of the block.\n+ * @order: order of the allocation.\n+ *\n+ * Instructs KHO to unpreserve a high-order block that was preserved by\n+ * kho_preserve_page() before.\n+ */\n+void kho_unpreserve_page(struct page *page, unsigned int order)\n+{\n+\tstruct kho_radix_tree *tree = \u0026kho_out.radix_tree;\n+\tconst unsigned long pfn = page_to_pfn(page);\n+\n+\tkho_radix_del_page(tree, pfn, order);\n+}\n+EXPORT_SYMBOL_GPL(kho_unpreserve_page);\n+\n static unsigned int __kho_preserve_pages_order(unsigned long start_pfn,\n \t\t\t\t\t       unsigned long end_pfn)\n {\n@@ -918,7 +1000,8 @@ static void __kho_unpreserve(struct kho_radix_tree *tree,\n  * @nr_pages: number of pages.\n  *\n  * Preserve a contiguous list of order 0 pages. Must be restored using\n- * kho_restore_pages() to ensure the pages are restored properly as order 0.\n+ * kho_restore_pages() to ensure the pages are restored properly as order 0\n+ * with each page having a reference count of 1 (split).\n  *\n  * Return: 0 on success, error code on failure\n  */\n"
}

best-expensive

null

{
  "EnableConfigs": null,
  "FocusSymbols": [],
  "Reasoning": "The patch introduces new APIs (`kho_preserve_page`, `kho_unpreserve_page`, `kho_restore_page`) for Kexec Handover (KHO) which are currently unused anywhere in the kernel tree. It also refactors `kho_restore_folio` and `kho_restore_pages` to use a new internal helper `__kho_restore_page`, and modifies `kho_init_high_order_page` to clear page tags for tail pages. However, all of these modified code paths are only reachable during the KHO restore phase, which strictly requires the kernel to be booted with KHO data passed from a previous kernel. Since syzkaller boots from a fresh VM image without KHO data, this code is completely unreachable in a standard fuzzing environment.",
  "WorthFuzzing": false
}

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).
- Code in vendor-specific PCIe switch, SmartNIC, or GPU drivers (e.g., mlxsw, pds_core, qed,
  ionic, amdgpu) that require physical PCIe hardware cards not emulated in standard QEMU.
- Driver .remove, .shutdown, or pci_unregister_driver teardown callbacks (e.g., igb_remove)
  that are executed only during PCI hot-unplug or sysfs driver unbind operations.

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.
   Prefer non-static, non-inlined API entrypoint functions over internal static helper functions
   (which are inlined by the compiler and do not have distinct symbol addresses).
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.
   Also check "depends on" lines in Kconfig to include any non-standard parent subsystem configs
   needed for Kbuild to compile the code statically into vmlinux. 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 c8d66e8c1c74d3d08640eb0a8fd77ed6b728885e
Author: syz-cluster <triage@syzkaller.com>
Date:   Mon Aug 3 17:06:32 2026 +0000

    syz-cluster: applied patch under review

diff --git a/include/linux/kexec_handover.h b/include/linux/kexec_handover.h
index 8968c56d2d73e..6e2c75b16209c 100644
--- a/include/linux/kexec_handover.h
+++ b/include/linux/kexec_handover.h
@@ -22,6 +22,8 @@ bool is_kho_boot(void);
 
 int kho_preserve_folio(struct folio *folio);
 void kho_unpreserve_folio(struct folio *folio);
+int kho_preserve_page(struct page *page, unsigned int order);
+void kho_unpreserve_page(struct page *page, unsigned int order);
 int kho_preserve_pages(struct page *page, unsigned long nr_pages);
 void kho_unpreserve_pages(struct page *page, unsigned long nr_pages);
 int kho_preserve_vmalloc(void *ptr, struct kho_vmalloc *preservation);
@@ -30,6 +32,7 @@ void *kho_alloc_preserve(size_t size);
 void kho_unpreserve_free(void *mem);
 void kho_restore_free(void *mem);
 struct folio *kho_restore_folio(phys_addr_t phys);
+struct page *kho_restore_page(phys_addr_t phys);
 struct page *kho_restore_pages(phys_addr_t phys, unsigned long nr_pages);
 void *kho_restore_vmalloc(const struct kho_vmalloc *preservation);
 int kho_add_subtree(const char *name, void *blob, size_t size);
@@ -65,6 +68,13 @@ static inline int kho_preserve_pages(struct page *page, unsigned int nr_pages)
 
 static inline void kho_unpreserve_pages(struct page *page, unsigned int nr_pages) { }
 
+static inline int kho_preserve_page(struct page *page, unsigned int order)
+{
+	return -EOPNOTSUPP;
+}
+
+static inline void kho_unpreserve_page(struct page *page, unsigned int order) { }
+
 static inline int kho_preserve_vmalloc(void *ptr,
 				       struct kho_vmalloc *preservation)
 {
diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
index 4834a809985ab..dd41d324c213d 100644
--- a/kernel/liveupdate/kexec_handover.c
+++ b/kernel/liveupdate/kexec_handover.c
@@ -357,6 +357,24 @@ int kho_radix_walk_tree(struct kho_radix_tree *tree,
 }
 EXPORT_SYMBOL_GPL(kho_radix_walk_tree);
 
+/* For physically contiguous pages. */
+static void kho_init_high_order_page(struct page *page, unsigned int order)
+{
+	unsigned long nr_pages = (1UL << order);
+
+	/* Head page gets refcount of 1. */
+	set_page_count(page, 1);
+	/* Clear head page's codetag to avoid accounting mismatch. */
+	clear_page_tag_ref(page);
+
+	/* For high-order blocks, tail pages get a page count of zero. */
+	for (unsigned long i = 1; i < nr_pages; i++) {
+		set_page_count(page + i, 0);
+		/* Clear each page's codetag to avoid accounting mismatch. */
+		clear_page_tag_ref(page + i);
+	}
+}
+
 /* For physically contiguous 0-order pages. */
 static void kho_init_pages(struct page *page, unsigned long nr_pages)
 {
@@ -369,25 +387,15 @@ static void kho_init_pages(struct page *page, unsigned long nr_pages)
 
 static void kho_init_folio(struct page *page, unsigned int order)
 {
-	unsigned long nr_pages = (1 << order);
-
-	/* Head page gets refcount of 1. */
-	set_page_count(page, 1);
-	/* Clear head page's codetag to avoid accounting mismatch. */
-	clear_page_tag_ref(page);
-
-	/* For higher order folios, tail pages get a page count of zero. */
-	for (unsigned long i = 1; i < nr_pages; i++)
-		set_page_count(page + i, 0);
+	kho_init_high_order_page(page, order);
 
 	if (order > 0)
 		prep_compound_page(page, order);
 }
 
-static struct page *kho_restore_page(phys_addr_t phys, bool is_folio)
+static struct page *__kho_restore_page(phys_addr_t phys, unsigned int *order)
 {
 	struct page *page = pfn_to_online_page(PHYS_PFN(phys));
-	unsigned long nr_pages;
 	union kho_page_info info;
 
 	if (!page)
@@ -401,17 +409,14 @@ static struct page *kho_restore_page(phys_addr_t phys, bool is_folio)
 	 */
 	if (WARN_ON_ONCE(info.magic != KHO_PAGE_MAGIC))
 		return NULL;
-	nr_pages = (1 << info.order);
 
 	/* Clear private to make sure later restores on this page error out. */
 	page->private = 0;
+	if (order)
+		*order = info.order;
 
-	if (is_folio)
-		kho_init_folio(page, info.order);
-	else
-		kho_init_pages(page, nr_pages);
+	adjust_managed_page_count(page, 1UL << info.order);
 
-	adjust_managed_page_count(page, nr_pages);
 	return page;
 }
 
@@ -423,12 +428,41 @@ static struct page *kho_restore_page(phys_addr_t phys, bool is_folio)
  */
 struct folio *kho_restore_folio(phys_addr_t phys)
 {
-	struct page *page = kho_restore_page(phys, true);
+	unsigned int order;
+	struct page *page = __kho_restore_page(phys, &order);
+
+	if (!page)
+		return NULL;
+
+	kho_init_folio(page, order);
 
-	return page ? page_folio(page) : NULL;
+	return page_folio(page);
 }
 EXPORT_SYMBOL_GPL(kho_restore_folio);
 
+/**
+ * kho_restore_page - restore a high-order page block.
+ * @phys: physical address of the first page.
+ *
+ * Restore a high-order page block that was preserved with
+ * kho_preserve_page().
+ *
+ * Return: the head page on success, NULL on failure.
+ */
+struct page *kho_restore_page(phys_addr_t phys)
+{
+	unsigned int order;
+	struct page *page = __kho_restore_page(phys, &order);
+
+	if (!page)
+		return NULL;
+
+	kho_init_high_order_page(page, order);
+
+	return page;
+}
+EXPORT_SYMBOL_GPL(kho_restore_page);
+
 /**
  * kho_restore_pages - restore list of contiguous order 0 pages.
  * @phys: physical address of the first page.
@@ -448,10 +482,13 @@ struct page *kho_restore_pages(phys_addr_t phys, unsigned long nr_pages)
 	while (pfn < end_pfn) {
 		const unsigned int order =
 			min(count_trailing_zeros(pfn), ilog2(end_pfn - pfn));
-		struct page *page = kho_restore_page(PFN_PHYS(pfn), false);
+		unsigned int info_order;
+		struct page *page = __kho_restore_page(PFN_PHYS(pfn), &info_order);
 
 		if (!page)
 			return NULL;
+
+		kho_init_pages(page, 1UL << info_order);
 		pfn += 1 << order;
 	}
 
@@ -881,6 +918,51 @@ void kho_unpreserve_folio(struct folio *folio)
 }
 EXPORT_SYMBOL_GPL(kho_unpreserve_folio);
 
+/**
+ * kho_preserve_page - preserve a high-order page block.
+ * @page: head page of the block.
+ * @order: order of the allocation.
+ *
+ * Instructs KHO to preserve a high-order contiguous allocation (like a DMA
+ * buffer) as a single unit. It must be restored using kho_restore_page() to
+ * ensure the tail pages are correctly initialized with a zero refcount.
+ *
+ * If a driver needs to split a block that has been preserved with this
+ * function, it must first unpreserve the block using kho_unpreserve_page(),
+ * perform the split, and then re-preserve the individual pages using
+ * kho_preserve_pages().
+ *
+ * Return: 0 on success, error code on failure
+ */
+int kho_preserve_page(struct page *page, unsigned int order)
+{
+	struct kho_radix_tree *tree = &kho_out.radix_tree;
+	const unsigned long pfn = page_to_pfn(page);
+
+	if (WARN_ON(kho_scratch_overlap(pfn << PAGE_SHIFT, PAGE_SIZE << order)))
+		return -EINVAL;
+
+	return kho_radix_add_page(tree, pfn, order);
+}
+EXPORT_SYMBOL_GPL(kho_preserve_page);
+
+/**
+ * kho_unpreserve_page - unpreserve a high-order page block.
+ * @page: head page of the block.
+ * @order: order of the allocation.
+ *
+ * Instructs KHO to unpreserve a high-order block that was preserved by
+ * kho_preserve_page() before.
+ */
+void kho_unpreserve_page(struct page *page, unsigned int order)
+{
+	struct kho_radix_tree *tree = &kho_out.radix_tree;
+	const unsigned long pfn = page_to_pfn(page);
+
+	kho_radix_del_page(tree, pfn, order);
+}
+EXPORT_SYMBOL_GPL(kho_unpreserve_page);
+
 static unsigned int __kho_preserve_pages_order(unsigned long start_pfn,
 					       unsigned long end_pfn)
 {
@@ -918,7 +1000,8 @@ static void __kho_unpreserve(struct kho_radix_tree *tree,
  * @nr_pages: number of pages.
  *
  * Preserve a contiguous list of order 0 pages. Must be restored using
- * kho_restore_pages() to ensure the pages are restored properly as order 0.
+ * kho_restore_pages() to ensure the pages are restored properly as order 0
+ * with each page having a reference count of 1 (split).
  *
  * Return: 0 on success, error code on failure
  */

gemini-3.1-pro-preview

null

null

							input: 4704
							output: 21
							thoughts: 123
						

**Analyzing the Kexec Handover Patch**

Alright, let's dive into this patch. It looks like we've got some new functions being introduced: `kho_preserve_page`, `kho_unpreserve_page`, and `kho_restore_page`, all residing within `kernel/liveupdate/kexec_handover.c`. Naturally, `kexec_handover.h` has been modified to accommodate these additions. The core theme here is "kexec handover" or KHO, and from the function names, I'm guessing this patch has something to do with managing those high-order page blocks during the handover process. My immediate thought is, "Is this functionality even enabled in our current configuration?" Gotta be sure we're actually *using* this before I go too deep. I'll get `grepper` fired up and search for occurrences of `kho_preserve_page` and, just to be thorough, `CONFIG_KEXEC_HANDOVER`. That should give me a quick understanding of whether this KHO feature is even reachable in the first place.

{
  "Expression": "CONFIG_KEXEC_HANDOVER"
}

{
  "Output": "Documentation/admin-guide/mm/kho.rst=14=Prerequisites\n--\nDocumentation/admin-guide/mm/kho.rst-16-\nDocumentation/admin-guide/mm/kho.rst:17:KHO is available when the kernel is compiled with ``CONFIG_KEXEC_HANDOVER``\nDocumentation/admin-guide/mm/kho.rst-18-set to y. Every KHO producer may have its own config option that you\n--\nDocumentation/admin-guide/mm/kho.rst=87=These debugfs interfaces are available when the kernel is compiled with\nDocumentation/admin-guide/mm/kho.rst:88:``CONFIG_KEXEC_HANDOVER_DEBUGFS`` enabled.\nDocumentation/admin-guide/mm/kho.rst-89-\n--\narch/x86/boot/compressed/kaslr.c=768=static bool process_kho_entries(unsigned long minimum, unsigned long image_size)\n--\narch/x86/boot/compressed/kaslr.c-774-\narch/x86/boot/compressed/kaslr.c:775:\tif (!IS_ENABLED(CONFIG_KEXEC_HANDOVER))\narch/x86/boot/compressed/kaslr.c-776-\t\treturn false;\n--\narch/x86/kernel/kexec-bzimage64.c=274=static void setup_kho(const struct kimage *image, struct boot_params *params,\n--\narch/x86/kernel/kexec-bzimage64.c-280-\narch/x86/kernel/kexec-bzimage64.c:281:\tif (!IS_ENABLED(CONFIG_KEXEC_HANDOVER))\narch/x86/kernel/kexec-bzimage64.c-282-\t\treturn;\n--\narch/x86/kernel/kexec-bzimage64.c=301=setup_boot_parameters(struct kimage *image, struct boot_params *params,\n--\narch/x86/kernel/kexec-bzimage64.c-390-\narch/x86/kernel/kexec-bzimage64.c:391:\tif (IS_ENABLED(CONFIG_KEXEC_HANDOVER)) {\narch/x86/kernel/kexec-bzimage64.c-392-\t\t/* Setup space to store preservation metadata */\n--\narch/x86/kernel/kexec-bzimage64.c=475=static void *bzImage64_load(struct kimage *image, char *kernel,\n--\narch/x86/kernel/kexec-bzimage64.c-581-\narch/x86/kernel/kexec-bzimage64.c:582:\tif (IS_ENABLED(CONFIG_KEXEC_HANDOVER))\narch/x86/kernel/kexec-bzimage64.c-583-\t\tkbuf.bufsz += sizeof(struct setup_data) +\n--\narch/x86/kernel/setup.c=456=static void __init add_kho(u64 phys_addr, u32 data_len)\n--\narch/x86/kernel/setup.c-461-\narch/x86/kernel/setup.c:462:\tif (!IS_ENABLED(CONFIG_KEXEC_HANDOVER)) {\narch/x86/kernel/setup.c:463:\t\tpr_warn(\"Passed KHO data, but CONFIG_KEXEC_HANDOVER not set. Ignoring.\\n\");\narch/x86/kernel/setup.c-464-\t\treturn;\n--\ndrivers/of/fdt.c=928=static void __init early_init_dt_check_kho(void)\n--\ndrivers/of/fdt.c-932-\ndrivers/of/fdt.c:933:\tif (!IS_ENABLED(CONFIG_KEXEC_HANDOVER) || (long)node \u003c 0)\ndrivers/of/fdt.c-934-\t\treturn;\n--\ndrivers/of/kexec.c=258=static int kho_add_chosen(const struct kimage *image, void *fdt, int chosen_node)\n--\ndrivers/of/kexec.c-260-\tint ret = 0;\ndrivers/of/kexec.c:261:#ifdef CONFIG_KEXEC_HANDOVER\ndrivers/of/kexec.c-262-\tphys_addr_t fdt_mem = 0;\n--\ndrivers/of/kexec.c-290-\ndrivers/of/kexec.c:291:#endif /* CONFIG_KEXEC_HANDOVER */\ndrivers/of/kexec.c-292-\treturn ret;\n--\ninclude/linux/kexec_handover.h=17=struct page;\ninclude/linux/kexec_handover.h-18-\ninclude/linux/kexec_handover.h:19:#ifdef CONFIG_KEXEC_HANDOVER\ninclude/linux/kexec_handover.h-20-bool kho_is_enabled(void);\n--\ninclude/linux/kexec_handover.h=125=static inline void kho_populate(phys_addr_t fdt_phys, u64 fdt_len,\n--\ninclude/linux/kexec_handover.h-128-}\ninclude/linux/kexec_handover.h:129:#endif /* CONFIG_KEXEC_HANDOVER */\ninclude/linux/kexec_handover.h-130-\n--\ninclude/linux/kho_radix_tree.h=37=typedef int (*kho_radix_tree_walk_callback_t)(phys_addr_t phys,\n--\ninclude/linux/kho_radix_tree.h-39-\ninclude/linux/kho_radix_tree.h:40:#ifdef CONFIG_KEXEC_HANDOVER\ninclude/linux/kho_radix_tree.h-41-\n--\ninclude/linux/kho_radix_tree.h=48=int kho_radix_walk_tree(struct kho_radix_tree *tree,\n--\ninclude/linux/kho_radix_tree.h-50-\ninclude/linux/kho_radix_tree.h:51:#else  /* #ifdef CONFIG_KEXEC_HANDOVER */\ninclude/linux/kho_radix_tree.h-52-\n--\ninclude/linux/kho_radix_tree.h=62=static inline int kho_radix_walk_tree(struct kho_radix_tree *tree,\n--\ninclude/linux/kho_radix_tree.h-67-\ninclude/linux/kho_radix_tree.h:68:#endif /* #ifdef CONFIG_KEXEC_HANDOVER */\ninclude/linux/kho_radix_tree.h-69-\n--\nkernel/kexec_internal.h=43=struct kexec_buf;\nkernel/kexec_internal.h-44-\nkernel/kexec_internal.h:45:#ifdef CONFIG_KEXEC_HANDOVER\nkernel/kexec_internal.h-46-int kho_locate_mem_hole(struct kexec_buf *kbuf,\n--\nkernel/kexec_internal.h=56=static inline int kho_fill_kimage(struct kimage *image) { return 0; }\nkernel/kexec_internal.h:57:#endif /* CONFIG_KEXEC_HANDOVER */\nkernel/kexec_internal.h-58-#endif /* LINUX_KEXEC_INTERNAL_H */\n--\nkernel/liveupdate/Makefile=3=luo-y :=\t\t\t\t\t\t\t\t\\\n--\nkernel/liveupdate/Makefile-9-\nkernel/liveupdate/Makefile:10:obj-$(CONFIG_KEXEC_HANDOVER)\t\t+= kexec_handover.o\nkernel/liveupdate/Makefile:11:obj-$(CONFIG_KEXEC_HANDOVER_DEBUG)\t+= kexec_handover_debug.o\nkernel/liveupdate/Makefile:12:obj-$(CONFIG_KEXEC_HANDOVER_DEBUGFS)\t+= kexec_handover_debugfs.o\nkernel/liveupdate/Makefile-13-\n--\nkernel/liveupdate/kexec_handover.c=56=static_assert(sizeof(union kho_page_info) == sizeof(((struct page *)0)-\u003eprivate));\nkernel/liveupdate/kexec_handover.c-57-\nkernel/liveupdate/kexec_handover.c:58:static bool kho_enable __ro_after_init = IS_ENABLED(CONFIG_KEXEC_HANDOVER_ENABLE_DEFAULT);\nkernel/liveupdate/kexec_handover.c-59-\n--\nkernel/liveupdate/kexec_handover.c=708=static void __init kho_reserve_scratch(void)\n--\nkernel/liveupdate/kexec_handover.c-797- * ``/sys/kernel/debug/kho/out/sub_fdts/@name`` when kernel is configured with\nkernel/liveupdate/kexec_handover.c:798: * CONFIG_KEXEC_HANDOVER_DEBUGFS\nkernel/liveupdate/kexec_handover.c-799- *\n--\nkernel/liveupdate/kexec_handover_internal.h-8-\nkernel/liveupdate/kexec_handover_internal.h:9:#ifdef CONFIG_KEXEC_HANDOVER_DEBUGFS\nkernel/liveupdate/kexec_handover_internal.h-10-#include \u003clinux/debugfs.h\u003e\n--\nkernel/liveupdate/kexec_handover_internal.h=23=extern unsigned int kho_scratch_cnt;\nkernel/liveupdate/kexec_handover_internal.h-24-\nkernel/liveupdate/kexec_handover_internal.h:25:#ifdef CONFIG_KEXEC_HANDOVER_DEBUGFS\nkernel/liveupdate/kexec_handover_internal.h-26-int kho_debugfs_init(void);\n--\nkernel/liveupdate/kexec_handover_internal.h=40=static inline void kho_debugfs_blob_remove(struct kho_debugfs *dbg,\nkernel/liveupdate/kexec_handover_internal.h-41-\t\t\t\t\t   void *blob) { }\nkernel/liveupdate/kexec_handover_internal.h:42:#endif /* CONFIG_KEXEC_HANDOVER_DEBUGFS */\nkernel/liveupdate/kexec_handover_internal.h-43-\nkernel/liveupdate/kexec_handover_internal.h:44:#ifdef CONFIG_KEXEC_HANDOVER_DEBUG\nkernel/liveupdate/kexec_handover_internal.h-45-bool kho_scratch_overlap(phys_addr_t phys, size_t size);\n--\nkernel/liveupdate/kexec_handover_internal.h=47=static inline bool kho_scratch_overlap(phys_addr_t phys, size_t size)\n--\nkernel/liveupdate/kexec_handover_internal.h-50-}\nkernel/liveupdate/kexec_handover_internal.h:51:#endif /* CONFIG_KEXEC_HANDOVER_DEBUG */\nkernel/liveupdate/kexec_handover_internal.h-52-\n--\nmm/memblock.c-21-\nmm/memblock.c:22:#ifdef CONFIG_KEXEC_HANDOVER\nmm/memblock.c-23-#include \u003clinux/libfdt.h\u003e\n--\nmm/memblock.c-25-#include \u003clinux/kho/abi/memblock.h\u003e\nmm/memblock.c:26:#endif /* CONFIG_KEXEC_HANDOVER */\nmm/memblock.c-27-\n--\nmm/memblock.c=2515=bool __init_memblock memblock_is_kho_scratch_memory(phys_addr_t addr)\n--\nmm/memblock.c-2525-\nmm/memblock.c:2526:#ifdef CONFIG_KEXEC_HANDOVER\nmm/memblock.c-2527-\n--\nmm/memblock.c=2708=static bool __init reserve_mem_kho_revive(const char *name, phys_addr_t size,\n--\nmm/memblock.c-2712-}\nmm/memblock.c:2713:#endif /* CONFIG_KEXEC_HANDOVER */\nmm/memblock.c-2714-\n--\ntools/testing/selftests/kho/vmtest.sh=60=CONFIG_BLK_DEV_INITRD=y\ntools/testing/selftests/kho/vmtest.sh:61:CONFIG_KEXEC_HANDOVER=y\ntools/testing/selftests/kho/vmtest.sh:62:CONFIG_KEXEC_HANDOVER_DEBUG=y\ntools/testing/selftests/kho/vmtest.sh:63:CONFIG_KEXEC_HANDOVER_DEBUGFS=y\ntools/testing/selftests/kho/vmtest.sh-64-CONFIG_TEST_KEXEC_HANDOVER=y\n--\ntools/testing/selftests/liveupdate/config=2=CONFIG_KEXEC_FILE=y\ntools/testing/selftests/liveupdate/config:3:CONFIG_KEXEC_HANDOVER=y\ntools/testing/selftests/liveupdate/config:4:CONFIG_KEXEC_HANDOVER_ENABLE_DEFAULT=y\ntools/testing/selftests/liveupdate/config:5:CONFIG_KEXEC_HANDOVER_DEBUGFS=y\ntools/testing/selftests/liveupdate/config:6:CONFIG_KEXEC_HANDOVER_DEBUG=y\ntools/testing/selftests/liveupdate/config-7-CONFIG_LIVEUPDATE=y\n"
}

gemini-3.1-pro-preview

null

null

							input: 8380
							output: 19
							thoughts: 170
						

**Analyzing the Kexec Handover Patch**

Okay, so this patch is introducing three new functions: `kho_preserve_page`, `kho_unpreserve_page`, and `kho_restore_page`. They're being exported with `EXPORT_SYMBOL_GPL`, which is interesting. It strongly suggests these are intended for use by GPL-licensed kernel modules. And they're part of the Kexec Handover (KHO) feature, which is only enabled if `CONFIG_KEXEC_HANDOVER` is set. Right, KHO is all about preserving memory across a `kexec` call.

The core of this patch seems focused on handling high-order pages. That makes sense, as these are more likely to get fragmented and lost during a handover. The key question now becomes: is there any way for this to be called from user space? If so, that opens a huge can of worms in terms of security. KHO is a kernel-side feature, used by kexec, a mechanism to switch to a new kernel. So the intended consumers are definitely drivers. I need to understand the mechanism here: these functions, as APIs, are for drivers to preserve their own high-order pages during a `kexec`.

Now, the real value of the patch is going to depend on *who* is using it. Are there any drivers actually leveraging these APIs? That’s the critical piece of information. I'll need to do a quick search for `kho_preserve_page` within the codebase to see how it's being used. That'll tell me if this is purely theoretical or if this has any measurable effect on performance, stability, or security.

{
  "Expression": "kho_preserve_page"
}

{
  "Output": "include/linux/kexec_handover.h=24=void kho_unpreserve_folio(struct folio *folio);\ninclude/linux/kexec_handover.h:25:int kho_preserve_page(struct page *page, unsigned int order);\ninclude/linux/kexec_handover.h-26-void kho_unpreserve_page(struct page *page, unsigned int order);\ninclude/linux/kexec_handover.h:27:int kho_preserve_pages(struct page *page, unsigned long nr_pages);\ninclude/linux/kexec_handover.h-28-void kho_unpreserve_pages(struct page *page, unsigned long nr_pages);\n--\ninclude/linux/kexec_handover.h=62=static inline void kho_unpreserve_folio(struct folio *folio) { }\ninclude/linux/kexec_handover.h-63-\ninclude/linux/kexec_handover.h:64:static inline int kho_preserve_pages(struct page *page, unsigned int nr_pages)\ninclude/linux/kexec_handover.h-65-{\n--\ninclude/linux/kexec_handover.h=69=static inline void kho_unpreserve_pages(struct page *page, unsigned int nr_pages) { }\ninclude/linux/kexec_handover.h-70-\ninclude/linux/kexec_handover.h:71:static inline int kho_preserve_page(struct page *page, unsigned int order)\ninclude/linux/kexec_handover.h-72-{\n--\nkernel/liveupdate/kexec_handover.c=441=EXPORT_SYMBOL_GPL(kho_restore_folio);\n--\nkernel/liveupdate/kexec_handover.c-447- * Restore a high-order page block that was preserved with\nkernel/liveupdate/kexec_handover.c:448: * kho_preserve_page().\nkernel/liveupdate/kexec_handover.c-449- *\n--\nkernel/liveupdate/kexec_handover.c=464=EXPORT_SYMBOL_GPL(kho_restore_page);\n--\nkernel/liveupdate/kexec_handover.c-471- * Restore a contiguous list of order 0 pages that was preserved with\nkernel/liveupdate/kexec_handover.c:472: * kho_preserve_pages().\nkernel/liveupdate/kexec_handover.c-473- *\n--\nkernel/liveupdate/kexec_handover.c=919=EXPORT_SYMBOL_GPL(kho_unpreserve_folio);\n--\nkernel/liveupdate/kexec_handover.c-921-/**\nkernel/liveupdate/kexec_handover.c:922: * kho_preserve_page - preserve a high-order page block.\nkernel/liveupdate/kexec_handover.c-923- * @page: head page of the block.\n--\nkernel/liveupdate/kexec_handover.c-932- * perform the split, and then re-preserve the individual pages using\nkernel/liveupdate/kexec_handover.c:933: * kho_preserve_pages().\nkernel/liveupdate/kexec_handover.c-934- *\n--\nkernel/liveupdate/kexec_handover.c-936- */\nkernel/liveupdate/kexec_handover.c:937:int kho_preserve_page(struct page *page, unsigned int order)\nkernel/liveupdate/kexec_handover.c-938-{\n--\nkernel/liveupdate/kexec_handover.c-946-}\nkernel/liveupdate/kexec_handover.c:947:EXPORT_SYMBOL_GPL(kho_preserve_page);\nkernel/liveupdate/kexec_handover.c-948-\n--\nkernel/liveupdate/kexec_handover.c-954- * Instructs KHO to unpreserve a high-order block that was preserved by\nkernel/liveupdate/kexec_handover.c:955: * kho_preserve_page() before.\nkernel/liveupdate/kexec_handover.c-956- */\n--\nkernel/liveupdate/kexec_handover.c=964=EXPORT_SYMBOL_GPL(kho_unpreserve_page);\nkernel/liveupdate/kexec_handover.c-965-\nkernel/liveupdate/kexec_handover.c:966:static unsigned int __kho_preserve_pages_order(unsigned long start_pfn,\nkernel/liveupdate/kexec_handover.c-967-\t\t\t\t\t       unsigned long end_pfn)\n--\nkernel/liveupdate/kexec_handover.c=983=static void __kho_unpreserve(struct kho_radix_tree *tree,\n--\nkernel/liveupdate/kexec_handover.c-988-\twhile (pfn \u003c end_pfn) {\nkernel/liveupdate/kexec_handover.c:989:\t\torder = __kho_preserve_pages_order(pfn, end_pfn);\nkernel/liveupdate/kexec_handover.c-990-\n--\nkernel/liveupdate/kexec_handover.c-997-/**\nkernel/liveupdate/kexec_handover.c:998: * kho_preserve_pages - preserve contiguous pages across kexec\nkernel/liveupdate/kexec_handover.c-999- * @page: first page in the list.\n--\nkernel/liveupdate/kexec_handover.c-1007- */\nkernel/liveupdate/kexec_handover.c:1008:int kho_preserve_pages(struct page *page, unsigned long nr_pages)\nkernel/liveupdate/kexec_handover.c-1009-{\n--\nkernel/liveupdate/kexec_handover.c-1022-\twhile (pfn \u003c end_pfn) {\nkernel/liveupdate/kexec_handover.c:1023:\t\tunsigned int order = __kho_preserve_pages_order(pfn, end_pfn);\nkernel/liveupdate/kexec_handover.c-1024-\n--\nkernel/liveupdate/kexec_handover.c-1038-}\nkernel/liveupdate/kexec_handover.c:1039:EXPORT_SYMBOL_GPL(kho_preserve_pages);\nkernel/liveupdate/kexec_handover.c-1040-\n--\nkernel/liveupdate/kexec_handover.c-1047- * This must be called with the same @page and @nr_pages as the corresponding\nkernel/liveupdate/kexec_handover.c:1048: * kho_preserve_pages() call. Unpreserving arbitrary sub-ranges of larger\nkernel/liveupdate/kexec_handover.c-1049- * preserved blocks is not supported.\n--\nkernel/liveupdate/kexec_handover.c=1092=static struct kho_vmalloc_chunk *new_vmalloc_chunk(struct kho_vmalloc_chunk *cur)\n--\nkernel/liveupdate/kexec_handover.c-1100-\nkernel/liveupdate/kexec_handover.c:1101:\terr = kho_preserve_pages(virt_to_page(chunk), 1);\nkernel/liveupdate/kexec_handover.c-1102-\tif (err)\n--\nkernel/liveupdate/kexec_handover.c=1142=int kho_preserve_vmalloc(void *ptr, struct kho_vmalloc *preservation)\n--\nkernel/liveupdate/kexec_handover.c-1167-\nkernel/liveupdate/kexec_handover.c:1168:\t\terr = kho_preserve_pages(vm-\u003epages[i], nr_contig_pages);\nkernel/liveupdate/kexec_handover.c-1169-\t\tif (err)\n--\nmm/memblock.c=2528=static int __init reserved_mem_preserve(void)\n--\nmm/memblock.c-2537-\nmm/memblock.c:2538:\t\terr = kho_preserve_pages(page, nr_pages);\nmm/memblock.c-2539-\t\tif (err)\n--\nmm/memblock.c=2557=static int __init prepare_kho_fdt(void)\n--\nmm/memblock.c-2569-\tfdt = page_to_virt(fdt_page);\nmm/memblock.c:2570:\terr = kho_preserve_pages(fdt_page, 1);\nmm/memblock.c-2571-\tif (err)\n"
}

gemini-3.1-pro-preview

null

null

							input: 11063
							output: 19
							thoughts: 77
						

Okay, let's see what we have here.

**Initial Assessment of the Memory Management Patch**

Alright, this patch introduces `kho_preserve_page`, `kho_unpreserve_page`, and `kho_restore_page`. That's interesting, potential new primitives for page management, perhaps some form of caching or delayed freeing? But hold on a second... running a quick `grep` confirms my suspicion: `kho_preserve_page` isn't *actually* being used anywhere in the kernel source, at least not yet. That's a red flag. Before I dig deeper into the intricacies of these functions, I need to understand the calling context. Let's make sure that `kho_preserve_page` or `kho_restore_page` aren't being called by something else. Back to the `grep`, I'll check for any immediate callers of those functions.

{
  "Expression": "kho_restore_page"
}

{
  "Output": "include/linux/kexec_handover.h=34=struct folio *kho_restore_folio(phys_addr_t phys);\ninclude/linux/kexec_handover.h:35:struct page *kho_restore_page(phys_addr_t phys);\ninclude/linux/kexec_handover.h:36:struct page *kho_restore_pages(phys_addr_t phys, unsigned long nr_pages);\ninclude/linux/kexec_handover.h-37-void *kho_restore_vmalloc(const struct kho_vmalloc *preservation);\n--\ninclude/linux/kexec_handover.h=94=static inline struct folio *kho_restore_folio(phys_addr_t phys)\n--\ninclude/linux/kexec_handover.h-98-\ninclude/linux/kexec_handover.h:99:static inline struct page *kho_restore_pages(phys_addr_t phys,\ninclude/linux/kexec_handover.h-100-\t\t\t\t\t     unsigned int nr_pages)\n--\nkernel/liveupdate/kexec_handover.c=388=static void kho_init_folio(struct page *page, unsigned int order)\n--\nkernel/liveupdate/kexec_handover.c-395-\nkernel/liveupdate/kexec_handover.c:396:static struct page *__kho_restore_page(phys_addr_t phys, unsigned int *order)\nkernel/liveupdate/kexec_handover.c-397-{\n--\nkernel/liveupdate/kexec_handover.c=429=struct folio *kho_restore_folio(phys_addr_t phys)\n--\nkernel/liveupdate/kexec_handover.c-431-\tunsigned int order;\nkernel/liveupdate/kexec_handover.c:432:\tstruct page *page = __kho_restore_page(phys, \u0026order);\nkernel/liveupdate/kexec_handover.c-433-\n--\nkernel/liveupdate/kexec_handover.c=441=EXPORT_SYMBOL_GPL(kho_restore_folio);\n--\nkernel/liveupdate/kexec_handover.c-443-/**\nkernel/liveupdate/kexec_handover.c:444: * kho_restore_page - restore a high-order page block.\nkernel/liveupdate/kexec_handover.c-445- * @phys: physical address of the first page.\n--\nkernel/liveupdate/kexec_handover.c-451- */\nkernel/liveupdate/kexec_handover.c:452:struct page *kho_restore_page(phys_addr_t phys)\nkernel/liveupdate/kexec_handover.c-453-{\nkernel/liveupdate/kexec_handover.c-454-\tunsigned int order;\nkernel/liveupdate/kexec_handover.c:455:\tstruct page *page = __kho_restore_page(phys, \u0026order);\nkernel/liveupdate/kexec_handover.c-456-\n--\nkernel/liveupdate/kexec_handover.c-463-}\nkernel/liveupdate/kexec_handover.c:464:EXPORT_SYMBOL_GPL(kho_restore_page);\nkernel/liveupdate/kexec_handover.c-465-\nkernel/liveupdate/kexec_handover.c-466-/**\nkernel/liveupdate/kexec_handover.c:467: * kho_restore_pages - restore list of contiguous order 0 pages.\nkernel/liveupdate/kexec_handover.c-468- * @phys: physical address of the first page.\n--\nkernel/liveupdate/kexec_handover.c-475- */\nkernel/liveupdate/kexec_handover.c:476:struct page *kho_restore_pages(phys_addr_t phys, unsigned long nr_pages)\nkernel/liveupdate/kexec_handover.c-477-{\n--\nkernel/liveupdate/kexec_handover.c-485-\t\tunsigned int info_order;\nkernel/liveupdate/kexec_handover.c:486:\t\tstruct page *page = __kho_restore_page(PFN_PHYS(pfn), \u0026info_order);\nkernel/liveupdate/kexec_handover.c-487-\n--\nkernel/liveupdate/kexec_handover.c-496-}\nkernel/liveupdate/kexec_handover.c:497:EXPORT_SYMBOL_GPL(kho_restore_pages);\nkernel/liveupdate/kexec_handover.c-498-\n--\nkernel/liveupdate/kexec_handover.c=919=EXPORT_SYMBOL_GPL(kho_unpreserve_folio);\n--\nkernel/liveupdate/kexec_handover.c-926- * Instructs KHO to preserve a high-order contiguous allocation (like a DMA\nkernel/liveupdate/kexec_handover.c:927: * buffer) as a single unit. It must be restored using kho_restore_page() to\nkernel/liveupdate/kexec_handover.c-928- * ensure the tail pages are correctly initialized with a zero refcount.\n--\nkernel/liveupdate/kexec_handover.c=983=static void __kho_unpreserve(struct kho_radix_tree *tree,\n--\nkernel/liveupdate/kexec_handover.c-1002- * Preserve a contiguous list of order 0 pages. Must be restored using\nkernel/liveupdate/kexec_handover.c:1003: * kho_restore_pages() to ensure the pages are restored properly as order 0\nkernel/liveupdate/kexec_handover.c-1004- * with each page having a reference count of 1 (split).\n--\nkernel/liveupdate/kexec_handover.c=1227=void *kho_restore_vmalloc(const struct kho_vmalloc *preservation)\n--\nkernel/liveupdate/kexec_handover.c-1260-\nkernel/liveupdate/kexec_handover.c:1261:\t\t\tpage = kho_restore_pages(phys, contig_pages);\nkernel/liveupdate/kexec_handover.c-1262-\t\t\tif (!page)\n--\nkernel/liveupdate/kexec_handover.c-1270-\nkernel/liveupdate/kexec_handover.c:1271:\t\tpage = kho_restore_pages(virt_to_phys(chunk), 1);\nkernel/liveupdate/kexec_handover.c-1272-\t\tif (!page)\n"
}

gemini-3.1-pro-preview

null

null

							input: 12983
							output: 20
							thoughts: 41
						

Okay, here's my take on those thoughts, tailored for an expert audience:

**Unused Kernel Functions Investigation**

Hmm, `kho_preserve_page` and `kho_restore_page` are exported symbols. That immediately raises a red flag. Typically, kernel functions are exported for use by other modules or subsystems. But if they're *exported* and *unused* within the kernel's source tree itself, that's a potential issue. It suggests dead code, a possible oversight during development, or maybe even remnants of a refactoring that wasn't fully cleaned up.

Before I jump to any conclusions, I need to verify this claim. My immediate instinct is to check for any callers of those functions within the entire kernel codebase. I need to make *absolutely* sure there are no calls to those functions lurking somewhere unexpected, perhaps in a different architecture or a less-frequently audited section. I'll need to use my preferred tool to perform a comprehensive search through the source. Let me double-check that first... no point in assuming something I haven't confirmed.

{
  "Expression": "kho_preserve_page\\("
}

{
  "Output": "include/linux/kexec_handover.h=24=void kho_unpreserve_folio(struct folio *folio);\ninclude/linux/kexec_handover.h:25:int kho_preserve_page(struct page *page, unsigned int order);\ninclude/linux/kexec_handover.h-26-void kho_unpreserve_page(struct page *page, unsigned int order);\n--\ninclude/linux/kexec_handover.h=69=static inline void kho_unpreserve_pages(struct page *page, unsigned int nr_pages) { }\ninclude/linux/kexec_handover.h-70-\ninclude/linux/kexec_handover.h:71:static inline int kho_preserve_page(struct page *page, unsigned int order)\ninclude/linux/kexec_handover.h-72-{\n--\nkernel/liveupdate/kexec_handover.c=441=EXPORT_SYMBOL_GPL(kho_restore_folio);\n--\nkernel/liveupdate/kexec_handover.c-447- * Restore a high-order page block that was preserved with\nkernel/liveupdate/kexec_handover.c:448: * kho_preserve_page().\nkernel/liveupdate/kexec_handover.c-449- *\n--\nkernel/liveupdate/kexec_handover.c=919=EXPORT_SYMBOL_GPL(kho_unpreserve_folio);\n--\nkernel/liveupdate/kexec_handover.c-936- */\nkernel/liveupdate/kexec_handover.c:937:int kho_preserve_page(struct page *page, unsigned int order)\nkernel/liveupdate/kexec_handover.c-938-{\n--\nkernel/liveupdate/kexec_handover.c=947=EXPORT_SYMBOL_GPL(kho_preserve_page);\n--\nkernel/liveupdate/kexec_handover.c-954- * Instructs KHO to unpreserve a high-order block that was preserved by\nkernel/liveupdate/kexec_handover.c:955: * kho_preserve_page() before.\nkernel/liveupdate/kexec_handover.c-956- */\n"
}

gemini-3.1-pro-preview

null

null

							input: 13816
							output: 21
							thoughts: 38
						

Okay, here's my take on those thoughts, tailored for an expert audience:

**Investigating Memory Preservation/Restoration in the Kernel**

Alright, let's see... I'm looking at the call graph for `kho_preserve_page` and `kho_restore_page`. Huh, that's odd, according to the static analysis, neither of those functions seems to be directly called anywhere within the kernel code. That's unexpected. I would have assumed we'd find at least *some* instances, even in obscure corner cases. My immediate reaction is to double check my tooling, maybe the call graph generation is missing something, or there's some indirect call mechanism I'm not accounting for. 

But wait a minute, I'm missing one, what about `kho_unpreserve_page`? That one is related to the others, I need to check the call graph for that function as well, just in case there's some design using that in place of the others. That would be interesting, and worth investigating.

{
  "Expression": "kho_unpreserve_page\\("
}

{
  "Output": "include/linux/kexec_handover.h=25=int kho_preserve_page(struct page *page, unsigned int order);\ninclude/linux/kexec_handover.h:26:void kho_unpreserve_page(struct page *page, unsigned int order);\ninclude/linux/kexec_handover.h-27-int kho_preserve_pages(struct page *page, unsigned long nr_pages);\n--\ninclude/linux/kexec_handover.h=71=static inline int kho_preserve_page(struct page *page, unsigned int order)\n--\ninclude/linux/kexec_handover.h-75-\ninclude/linux/kexec_handover.h:76:static inline void kho_unpreserve_page(struct page *page, unsigned int order) { }\ninclude/linux/kexec_handover.h-77-\n--\nkernel/liveupdate/kexec_handover.c=919=EXPORT_SYMBOL_GPL(kho_unpreserve_folio);\n--\nkernel/liveupdate/kexec_handover.c-930- * If a driver needs to split a block that has been preserved with this\nkernel/liveupdate/kexec_handover.c:931: * function, it must first unpreserve the block using kho_unpreserve_page(),\nkernel/liveupdate/kexec_handover.c-932- * perform the split, and then re-preserve the individual pages using\n--\nkernel/liveupdate/kexec_handover.c=947=EXPORT_SYMBOL_GPL(kho_preserve_page);\n--\nkernel/liveupdate/kexec_handover.c-956- */\nkernel/liveupdate/kexec_handover.c:957:void kho_unpreserve_page(struct page *page, unsigned int order)\nkernel/liveupdate/kexec_handover.c-958-{\n"
}

gemini-3.1-pro-preview

null

null

							input: 14558
							output: 33
							thoughts: 61
						

**Initial Assessment: API Implementations**

Okay, so I'm looking at these new functions – they've been introduced as APIs, which is fine, that's how it starts, but they haven't actually been integrated into the kernel's core logic yet. My initial thought is, "Where are these being used? Where's the rubber meeting the road?" We have to test this.

My mind immediately jumps to testing. I need to figure out if there is any testing for these. I need to locate where tests are. Let's explore the testing directory, I’ll start by checking the `tools/testing/selftests/kho/` directory or perhaps `tools/testing/selftests/liveupdate/`. Let's see if either of these locations has any tests.

no matches

{
  "Expression": "kho_preserve_page",
  "PathPrefix": "tools/testing/selftests/"
}

{
  "error": "no matches"
}

gemini-3.1-pro-preview

null

null

							input: 14836
							output: 19
							thoughts: 199
						

**Unused Code and Potential KHO Implications**

Okay, so I'm looking at this patch and my initial thought is, "These functions are completely untouched, unused". If they aren't being used, then obviously, they aren't going to be hit by any fuzzing, that's just a given. But hold on a second… could there be some other Kernel Handover (KHO) mechanism that *could* reach them? Let's see... Ah, `kho_preserve_page` is an `EXPORT_SYMBOL_GPL` function, so it's intended for drivers to call. If no driver actually utilizes it, then it’s just dead code, a no-op.

Now, let me dig a bit deeper into this patch to see if anything else is happening. Okay, the file changes include modifications to `kernel/liveupdate/kexec_handover.c` and `include/linux/kexec_handover.h`. It looks like we're introducing `kho_preserve_page`, `kho_unpreserve_page`, `kho_restore_page` and, critically, modifying `kho_restore_folio` and `kho_restore_pages` to use `__kho_restore_page`. But wait, are `kho_restore_folio` and `kho_restore_pages` actually *used* anywhere? I need to verify their call sites; that's the key to understanding the full impact here. This could be a significant change if those functions are active.

{
  "Expression": "kho_restore_folio"
}

{
  "Output": "include/linux/kexec_handover.h=33=void kho_restore_free(void *mem);\ninclude/linux/kexec_handover.h:34:struct folio *kho_restore_folio(phys_addr_t phys);\ninclude/linux/kexec_handover.h-35-struct page *kho_restore_page(phys_addr_t phys);\n--\ninclude/linux/kexec_handover.h=92=static inline void kho_restore_free(void *mem) { }\ninclude/linux/kexec_handover.h-93-\ninclude/linux/kexec_handover.h:94:static inline struct folio *kho_restore_folio(phys_addr_t phys)\ninclude/linux/kexec_handover.h-95-{\n--\nkernel/liveupdate/kexec_handover.c=396=static struct page *__kho_restore_page(phys_addr_t phys, unsigned int *order)\n--\nkernel/liveupdate/kexec_handover.c-423-/**\nkernel/liveupdate/kexec_handover.c:424: * kho_restore_folio - recreates the folio from the preserved memory.\nkernel/liveupdate/kexec_handover.c-425- * @phys: physical address of the folio.\n--\nkernel/liveupdate/kexec_handover.c-428- */\nkernel/liveupdate/kexec_handover.c:429:struct folio *kho_restore_folio(phys_addr_t phys)\nkernel/liveupdate/kexec_handover.c-430-{\n--\nkernel/liveupdate/kexec_handover.c-440-}\nkernel/liveupdate/kexec_handover.c:441:EXPORT_SYMBOL_GPL(kho_restore_folio);\nkernel/liveupdate/kexec_handover.c-442-\n--\nkernel/liveupdate/kexec_handover.c=1388=void kho_restore_free(void *mem)\n--\nkernel/liveupdate/kexec_handover.c-1394-\nkernel/liveupdate/kexec_handover.c:1395:\tfolio = kho_restore_folio(__pa(mem));\nkernel/liveupdate/kexec_handover.c-1396-\tif (!WARN_ON(!folio))\n--\nlib/test_kho.c=235=static int kho_test_restore_data(const void *fdt, int node)\n--\nlib/test_kho.c-267-\nlib/test_kho.c:268:\t\tfolio = kho_restore_folio(phys);\nlib/test_kho.c-269-\t\tif (!folio)\n--\nmm/memfd_luo.c=362=static void memfd_luo_discard_folios(const struct memfd_luo_folio_ser *folios_ser,\n--\nmm/memfd_luo.c-375-\t\tphys = PFN_PHYS(pfolio-\u003epfn);\nmm/memfd_luo.c:376:\t\tfolio = kho_restore_folio(phys);\nmm/memfd_luo.c-377-\t\tif (!folio) {\n--\nmm/memfd_luo.c=417=static int memfd_luo_retrieve_folios(struct file *file,\n--\nmm/memfd_luo.c-437-\t\tphys = PFN_PHYS(pfolio-\u003epfn);\nmm/memfd_luo.c:438:\t\tfolio = kho_restore_folio(phys);\nmm/memfd_luo.c-439-\t\tif (!folio) {\n--\nmm/memfd_luo.c-507-\t\tphys = PFN_PHYS(pfolio-\u003epfn);\nmm/memfd_luo.c:508:\t\tfolio = kho_restore_folio(phys);\nmm/memfd_luo.c-509-\t\tif (folio)\n"
}

gemini-3.1-pro-preview

null

null

							input: 16362
							output: 19
							thoughts: 604
						

**Analyzing the Impact of the `kho_restore_folio` Patch**

Okay, so I see that `kho_restore_folio` is used in both `lib/test_kho.c` and `mm/memfd_luo.c`. This patch modifies the function. Let's dig in. I need to understand if the core functionality has changed or if it's just a refactoring.

Looking at the diff, it seems that the original `kho_restore_page` function, which served as the workhorse behind restoring pages, has now been split into `__kho_restore_page` and `kho_restore_folio`. The `kho_restore_page` function is removed in favour of using `kho_restore_folio` and now contains much cleaner logic.

The crucial change seems to involve the use of `order` which now seems to be passed by reference. I see that the `is_folio` flag has been removed. I am interested to see how that impacts the original behaviour.

I notice the original logic inside the `if (is_folio)` block is now in `kho_restore_folio` and, there's a new `order` variable, and its value is assigned to the `*order`. The new `__kho_restore_page` now receives an `order` pointer and `kho_init_folio` uses the restored `order`.

The core logic remains the same: retrieve a `struct page` given a physical address, validate a magic number, clear the `private` field, and then initialize the folio. It looks like the handling of the order has been made more explicit, and it's cleaner in the new refactoring.
The removal of the `is_folio` flag is interesting; the implication here is that `kho_restore_folio` now *always* assumes it's dealing with a folio.

I need to confirm if `kho_restore_pages` is still in use, or if this patch subsumes all its functionality. That will be the key to understanding the full scope of the change.

{
  "Expression": "kho_restore_pages"
}

{
  "Output": "include/linux/kexec_handover.h=35=struct page *kho_restore_page(phys_addr_t phys);\ninclude/linux/kexec_handover.h:36:struct page *kho_restore_pages(phys_addr_t phys, unsigned long nr_pages);\ninclude/linux/kexec_handover.h-37-void *kho_restore_vmalloc(const struct kho_vmalloc *preservation);\n--\ninclude/linux/kexec_handover.h=94=static inline struct folio *kho_restore_folio(phys_addr_t phys)\n--\ninclude/linux/kexec_handover.h-98-\ninclude/linux/kexec_handover.h:99:static inline struct page *kho_restore_pages(phys_addr_t phys,\ninclude/linux/kexec_handover.h-100-\t\t\t\t\t     unsigned int nr_pages)\n--\nkernel/liveupdate/kexec_handover.c=464=EXPORT_SYMBOL_GPL(kho_restore_page);\n--\nkernel/liveupdate/kexec_handover.c-466-/**\nkernel/liveupdate/kexec_handover.c:467: * kho_restore_pages - restore list of contiguous order 0 pages.\nkernel/liveupdate/kexec_handover.c-468- * @phys: physical address of the first page.\n--\nkernel/liveupdate/kexec_handover.c-475- */\nkernel/liveupdate/kexec_handover.c:476:struct page *kho_restore_pages(phys_addr_t phys, unsigned long nr_pages)\nkernel/liveupdate/kexec_handover.c-477-{\n--\nkernel/liveupdate/kexec_handover.c-496-}\nkernel/liveupdate/kexec_handover.c:497:EXPORT_SYMBOL_GPL(kho_restore_pages);\nkernel/liveupdate/kexec_handover.c-498-\n--\nkernel/liveupdate/kexec_handover.c=983=static void __kho_unpreserve(struct kho_radix_tree *tree,\n--\nkernel/liveupdate/kexec_handover.c-1002- * Preserve a contiguous list of order 0 pages. Must be restored using\nkernel/liveupdate/kexec_handover.c:1003: * kho_restore_pages() to ensure the pages are restored properly as order 0\nkernel/liveupdate/kexec_handover.c-1004- * with each page having a reference count of 1 (split).\n--\nkernel/liveupdate/kexec_handover.c=1227=void *kho_restore_vmalloc(const struct kho_vmalloc *preservation)\n--\nkernel/liveupdate/kexec_handover.c-1260-\nkernel/liveupdate/kexec_handover.c:1261:\t\t\tpage = kho_restore_pages(phys, contig_pages);\nkernel/liveupdate/kexec_handover.c-1262-\t\t\tif (!page)\n--\nkernel/liveupdate/kexec_handover.c-1270-\nkernel/liveupdate/kexec_handover.c:1271:\t\tpage = kho_restore_pages(virt_to_phys(chunk), 1);\nkernel/liveupdate/kexec_handover.c-1272-\t\tif (!page)\n"
}

gemini-3.1-pro-preview

null

null

							input: 18266
							output: 20
							thoughts: 30
						

Okay, here's my interpretation of those thoughts, framed as my own, given my expertise:

**Checking the Restoration Dependencies**

Alright, let me see... I'm looking at `kho_restore_pages` and how it's being used. It looks like it's employed within the `kho_restore_vmalloc` function. The key question now becomes, is `kho_restore_vmalloc` itself actually utilized anywhere? I need to trace the call graph further. If `kho_restore_vmalloc` is unused, then `kho_restore_pages` might be dead code as well, or at the very least, potentially only used in edge cases that need to be explicitly evaluated. It's all about ensuring that this particular restoration path remains relevant. I'll need to follow the connections and see where everything leads.

{
  "Expression": "kho_restore_vmalloc"
}

{
  "Output": "include/linux/kexec_handover.h=36=struct page *kho_restore_pages(phys_addr_t phys, unsigned long nr_pages);\ninclude/linux/kexec_handover.h:37:void *kho_restore_vmalloc(const struct kho_vmalloc *preservation);\ninclude/linux/kexec_handover.h-38-int kho_add_subtree(const char *name, void *blob, size_t size);\n--\ninclude/linux/kexec_handover.h=99=static inline struct page *kho_restore_pages(phys_addr_t phys,\n--\ninclude/linux/kexec_handover.h-104-\ninclude/linux/kexec_handover.h:105:static inline void *kho_restore_vmalloc(const struct kho_vmalloc *preservation)\ninclude/linux/kexec_handover.h-106-{\n--\nkernel/liveupdate/kexec_handover.c=1215=EXPORT_SYMBOL_GPL(kho_unpreserve_vmalloc);\n--\nkernel/liveupdate/kexec_handover.c-1217-/**\nkernel/liveupdate/kexec_handover.c:1218: * kho_restore_vmalloc - recreates and populates an area in vmalloc address\nkernel/liveupdate/kexec_handover.c-1219- * space from the preserved memory.\n--\nkernel/liveupdate/kexec_handover.c-1226- */\nkernel/liveupdate/kexec_handover.c:1227:void *kho_restore_vmalloc(const struct kho_vmalloc *preservation)\nkernel/liveupdate/kexec_handover.c-1228-{\n--\nkernel/liveupdate/kexec_handover.c-1312-}\nkernel/liveupdate/kexec_handover.c:1313:EXPORT_SYMBOL_GPL(kho_restore_vmalloc);\nkernel/liveupdate/kexec_handover.c-1314-\n--\nlib/test_kho.c=235=static int kho_test_restore_data(const void *fdt, int node)\n--\nlib/test_kho.c-257-\nlib/test_kho.c:258:\tfolios_info = kho_restore_vmalloc(folios_info_phys);\nlib/test_kho.c-259-\tif (!folios_info)\n--\nmm/memfd_luo.c=387=static void memfd_luo_finish(struct liveupdate_file_op_args *args)\n--\nmm/memfd_luo.c-404-\tif (ser-\u003enr_folios) {\nmm/memfd_luo.c:405:\t\tfolios_ser = kho_restore_vmalloc(\u0026ser-\u003efolios);\nmm/memfd_luo.c-406-\t\tif (!folios_ser)\n--\nmm/memfd_luo.c=518=static int memfd_luo_retrieve(struct liveupdate_file_op_args *args)\n--\nmm/memfd_luo.c-555-\tif (ser-\u003enr_folios) {\nmm/memfd_luo.c:556:\t\tfolios_ser = kho_restore_vmalloc(\u0026ser-\u003efolios);\nmm/memfd_luo.c-557-\t\tif (!folios_ser) {\n"
}

gemini-3.1-pro-preview

null

null

							input: 19338
							output: 17
							thoughts: 1082
						

**Analyzing the KHO Page Restore Patch**

Okay, let's break this down. My initial thought is to trace the usage of these functions. `kho_restore_pages` is used by `kho_restore_vmalloc`, which is then used by both `lib/test_kho.c` and `mm/memfd_luo.c`. This refactoring of `kho_restore_page` into `__kho_restore_page`, and exposing `kho_restore_page` as a new exported function, is interesting. It's used by `kho_restore_folio` and `kho_restore_pages` now too. Since `kho_restore_pages` is actually *used*, the logic in `__kho_restore_page` and `kho_init_pages` is definitely reachable.

Now, I'm focusing on the initialization and restoration logic. `kho_init_pages`, `kho_init_folio`, and `kho_init_high_order_page` are the key functions here. The code for `kho_init_high_order_page` caught my eye:

```c
+/* For physically contiguous pages. */
+static void kho_init_high_order_page(struct page *page, unsigned int order)
+{
+	unsigned long nr_pages = (1UL << order);
+
+	/* Head page gets refcount of 1. */
+	set_page_count(page, 1);
+	/* Clear head page's codetag to avoid accounting mismatch. */
+	clear_page_tag_ref(page);
+
+	/* For high-order blocks, tail pages get a page count of zero. */
+	for (unsigned long i = 1; i < nr_pages; i++) {
+		set_page_count(page + i, 0);
+		/* Clear each page's codetag to avoid accounting mismatch. */
+		clear_page_tag_ref(page + i);
+	}
+}
```

This is important because `kho_init_high_order_page` is called by `kho_init_folio` and `kho_restore_page`. `kho_init_folio` is called by `kho_restore_folio`, and `kho_restore_folio` is used by `memfd_luo_retrieve_folios` and `test_kho`.  So the new code in `kho_init_high_order_page` is definitely accessible. It’s essentially the same as the old `kho_init_folio`, but with a `clear_page_tag_ref(page + i)` added for the tail pages.

Let's look at the old `kho_init_folio` code:

```c
-static void kho_init_folio(struct page *page, unsigned int order)
-{
-	unsigned long nr_pages = (1 << order);
-
-	/* Head page gets refcount of 1. */
-	set_page_count(page, 1);
-	/* Clear head page's codetag to avoid accounting mismatch. */
-	clear_page_tag_ref(page);
-
-	/* For higher order folios, tail pages get a page count of zero. */
-	for (unsigned long i = 1; i < nr_pages; i++)
-		set_page_count(page + i, 0);
+	kho_init_high_order_page(page, order);
 
 	if (order > 0)
 		prep_compound_page(page, order);
 }
```

Right, it just moved the initialization of the high-order page to another function. It looks like the main change is the inclusion of `clear_page_tag_ref(page + i)` for tail pages in `kho_init_high_order_page`. We now have these new functions, `kho_preserve_page`, `kho_unpreserve_page`, and `kho_restore_page`. But those are *unused* at the moment.  The relevant changes are the refactoring using `__kho_restore_page`, and the addition of `clear_page_tag_ref(page + i)` in `kho_init_high_order_page`.

Okay, the crucial part: `clear_page_tag_ref` is now being called on tail pages. *That's* a functional change. It's designed to fix an accounting mismatch by clearing page tags for the tail pages, which is good. But is it worth spending time fuzzing for it?

`kho_restore_folio` is the main

{
  "Expression": "test_kho"
}

{
  "Output": "MAINTAINERS=14343=F:\tkernel/liveupdate/kexec_handover*\nMAINTAINERS:14344:F:\tlib/test_kho.c\nMAINTAINERS-14345-F:\ttools/testing/selftests/kho/\n--\nlib/Makefile=106=obj-$(CONFIG_TEST_OBJPOOL) += test_objpool.o\nlib/Makefile:107:obj-$(CONFIG_TEST_KEXEC_HANDOVER) += test_kho.o\nlib/Makefile-108-\n"
}

gemini-3.1-pro-preview

null

null

							input: 21612
							output: 30
							thoughts: 32
						

Okay, here's my summary, considering my expertise:

**Checking for Syzkaller-Triggerable Interfaces in `lib/test_kho.c`**

Alright, before I dive into fuzzing with syzkaller, I need to take a quick peek at `lib/test_kho.c`. My primary goal here is to determine whether this module, or any part of it, exposes a debugfs or sysfs interface. These are prime targets for syzkaller, as they often provide mechanisms to interact with kernel internals in ways that might be vulnerable to fuzzing. A debugfs or sysfs entry could be directly manipulated to feed unusual data or trigger specific code paths. If I can identify such an interface within this file, I can significantly narrow the scope of my fuzzing efforts and increase the likelihood of finding interesting bugs. Essentially, I'm trying to identify low-hanging fruit for syzkaller exploitation within the context of this specific code.

{
  "Expression": "module_init",
  "PathPrefix": "lib/test_kho.c"
}

{
  "Output": "lib/test_kho.c=314=static int __init kho_test_init(void)\n--\nlib/test_kho.c-339-}\nlib/test_kho.c:340:module_init(kho_test_init);\nlib/test_kho.c-341-\n"
}

gemini-3.1-pro-preview

null

null

							input: 21960
							output: 35
							thoughts: 21
						

Here's my analysis of the provided text, rendered as though I were thinking it:

**Diving into `kho_test_init`**

Alright, let's get down to it. The task before me is to understand `kho_test_init`.  My first instinct, as always, is to locate the source code. It's telling me to look in `lib/test_kho.c`, so that's where I'll start. This file likely holds the core implementation of the testing framework for, or related to, this `kho` module. I need to understand what this `kho_test_init` function *does*. Is it setting up test environments? Initializing shared resources? Perhaps registering test cases or fixtures? My experience tells me that `init` functions are usually critical setup routines. I'll be looking for memory allocations, file operations, global variable assignments, or any other operations that prime the system for testing. I'll need to pay close attention to the return value, too; is it a success indicator, or does it return a pointer to some testing context? This is my starting point, let's see what's in there.

{
  "File": "lib/test_kho.c",
  "FirstLine": 314,
  "LineCount": 30
}

{
  "Contents": " 314:\tstatic int __init kho_test_init(void)\n 315:\t{\n 316:\t\tphys_addr_t fdt_phys;\n 317:\t\tint err;\n 318:\t\n 319:\t\tif (!kho_is_enabled())\n 320:\t\t\treturn 0;\n 321:\t\n 322:\t\terr = kho_retrieve_subtree(KHO_TEST_FDT, \u0026fdt_phys, NULL);\n 323:\t\tif (!err) {\n 324:\t\t\terr = kho_test_restore(fdt_phys);\n 325:\t\t\tif (err)\n 326:\t\t\t\tpr_err(\"KHO restore failed\\n\");\n 327:\t\t\telse\n 328:\t\t\t\tpr_info(\"KHO restore succeeded\\n\");\n 329:\t\n 330:\t\t\treturn err;\n 331:\t\t}\n 332:\t\n 333:\t\tif (err != -ENOENT) {\n 334:\t\t\tpr_warn(\"failed to retrieve %s FDT: %d\\n\", KHO_TEST_FDT, err);\n 335:\t\t\treturn err;\n 336:\t\t}\n 337:\t\n 338:\t\treturn kho_test_save();\n 339:\t}\n 340:\tmodule_init(kho_test_init);\n 341:\t\n 342:\tstatic void kho_test_cleanup(void)\n 343:\t{\n"
}

gemini-3.1-pro-preview

null

null

							input: 22667
							output: 23
							thoughts: 112
						

**Analyzing the KHO Subsystem Initialization**

Okay, let's break down this `test_kho` behavior. My understanding is that this function, `test_kho`, is essentially an automatic test that kicks off upon module load. If it's baked into the kernel, it runs right at boot. The core logic here is interesting. When KHO is active, it attempts to fetch a subtree. If that fails with an -ENOENT, that's a key indicator—it means the subtree isn't there, so it calls `kho_test_save()`. This implies a single initial run, probably during system startup.

The implication here is that Syzkaller won't be able to easily trigger this repeatedly unless it has some mechanism for module unloading and reloading. Without that capability, it's essentially a one-shot process.

Now, that `memfd_luo` mention caught my attention. It's time to shift gears and delve into `memfd_luo_retrieve_folios` to see if there's any related functionality that needs evaluation.

{
  "Expression": "memfd_luo_retrieve_folios"
}

{
  "Output": "mm/memfd_luo.c=387=static void memfd_luo_finish(struct liveupdate_file_op_args *args)\n--\nmm/memfd_luo.c-416-\nmm/memfd_luo.c:417:static int memfd_luo_retrieve_folios(struct file *file,\nmm/memfd_luo.c-418-\t\t\t\t     struct memfd_luo_folio_ser *folios_ser,\n--\nmm/memfd_luo.c=518=static int memfd_luo_retrieve(struct liveupdate_file_op_args *args)\n--\nmm/memfd_luo.c-561-\nmm/memfd_luo.c:562:\t\terr = memfd_luo_retrieve_folios(file, folios_ser, ser-\u003enr_folios);\nmm/memfd_luo.c-563-\t\tvfree(folios_ser);\n"
}

gemini-3.1-pro-preview

null

null

							input: 23279
							output: 21
							thoughts: 12
						

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

**Unpacking `memfd_luo_retrieve`**

Alright, so I'm presented with this term, `memfd_luo_retrieve`. My initial reaction is, "Hmm, never come across that specific function name before." Given my background, I immediately start breaking it down. `memfd` strongly suggests it deals with `memfd_create`, which, as we know, is a Linux-specific feature for creating anonymous, memory-backed files. That part's familiar territory – lightweight, ephemeral storage in memory, useful for security, IPC, and avoiding disk I/O. But the `luo_retrieve` bit… that’s what's intriguing. I have to guess it's specific to an extension or enhancement. Is this from a custom library? Maybe a specific project's implementation?

My mind is racing: I need to quickly establish the context. Is this related to data retrieval? Given the name, it *suggests* it, but without more context it's premature to jump to conclusions. Could it be about retrieving data from a previously created `memfd`? Maybe a control mechanism? I need to know how it's used. Is it a function for accessing the data, perhaps a form of data serialization for this type of file? Does it work only in this one system, or is it common in others?

My immediate steps would be to search for this function name within codebases I'm familiar with, or to start googling for documentation around memfd extensions. I'd be looking for a function signature, usage examples, and any explanations of its purpose. The goal is to rapidly determine what this extension does in relation to memfd.

{
  "Expression": "memfd_luo_retrieve"
}

{
  "Output": "mm/memfd_luo.c=387=static void memfd_luo_finish(struct liveupdate_file_op_args *args)\n--\nmm/memfd_luo.c-416-\nmm/memfd_luo.c:417:static int memfd_luo_retrieve_folios(struct file *file,\nmm/memfd_luo.c-418-\t\t\t\t     struct memfd_luo_folio_ser *folios_ser,\n--\nmm/memfd_luo.c-517-\nmm/memfd_luo.c:518:static int memfd_luo_retrieve(struct liveupdate_file_op_args *args)\nmm/memfd_luo.c-519-{\n--\nmm/memfd_luo.c-561-\nmm/memfd_luo.c:562:\t\terr = memfd_luo_retrieve_folios(file, folios_ser, ser-\u003enr_folios);\nmm/memfd_luo.c-563-\t\tvfree(folios_ser);\n--\nmm/memfd_luo.c=593=static const struct liveupdate_file_ops memfd_luo_file_ops = {\n--\nmm/memfd_luo.c-595-\t.finish = memfd_luo_finish,\nmm/memfd_luo.c:596:\t.retrieve = memfd_luo_retrieve,\nmm/memfd_luo.c-597-\t.preserve = memfd_luo_preserve,\n"
}

gemini-3.1-pro-preview

null

null

							input: 24084
							output: 20
							thoughts: 48
						

Okay, here's my interpretation of those thoughts, presented as my own mental process, given my expertise:

**Examining the Live Update File Operations**

Right, so `memfd_luo_file_ops` – that rings a bell. It's connected to `liveupdate_file_ops`. I know those are low-level file operation structures, usually providing custom implementations for specific functionalities. This suggests we're dealing with live updates, which automatically means I need to think about `CONFIG_LIVEUPDATE`. The key question popping into my head is, is that `CONFIG_LIVEUPDATE` functionality accessible from user space? That’s where the real complexity, and potential security implications, lie. If user space can trigger live updates, we've got a whole new level of concerns. I need to dig deeper into the code to trace the paths and security implications if this feature is available to user space.

{
  "Expression": "liveupdate_file_ops"
}

{
  "Output": "include/linux/liveupdate.h=46=struct liveupdate_file_op_args {\n--\ninclude/linux/liveupdate.h-54-/**\ninclude/linux/liveupdate.h:55: * struct liveupdate_file_ops - Callbacks for live-updatable files.\ninclude/linux/liveupdate.h-56- * @can_preserve: Required. Lightweight check to see if this handler is\n--\ninclude/linux/liveupdate.h-73- */\ninclude/linux/liveupdate.h:74:struct liveupdate_file_ops {\ninclude/linux/liveupdate.h-75-\tbool (*can_preserve)(struct liveupdate_file_handler *handler,\n--\ninclude/linux/liveupdate.h=101=struct liveupdate_file_handler {\ninclude/linux/liveupdate.h:102:\tconst struct liveupdate_file_ops *ops;\ninclude/linux/liveupdate.h-103-\tconst char compatible[LIVEUPDATE_HNDL_COMPAT_LENGTH];\n--\nmm/memfd_luo.c=588=static unsigned long memfd_luo_get_id(struct file *file)\n--\nmm/memfd_luo.c-592-\nmm/memfd_luo.c:593:static const struct liveupdate_file_ops memfd_luo_file_ops = {\nmm/memfd_luo.c-594-\t.freeze = memfd_luo_freeze,\n"
}

gemini-3.1-pro-preview

null

null

							input: 24717
							output: 20
							thoughts: 16
						

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

**Investigating the Usage of `liveupdate_file_ops`**

Right, so I need to understand where `liveupdate_file_ops` is actually being utilized within this system. That function name sounds like it's pretty critical for the live update process – dealing with file operations during an update, I'd imagine. Therefore, the first step is to trace its calls. I need to figure out the scope of its impact. Knowing where it’s called will provide a pretty solid understanding of the update flow. This will hopefully allow me to start tracing through its call stack to understand what functionality is impacted.

{
  "Expression": "liveupdate_file_handler"
}

{
  "Output": "include/linux/liveupdate.h-19-\ninclude/linux/liveupdate.h:20:struct liveupdate_file_handler;\ninclude/linux/liveupdate.h-21-struct liveupdate_flb;\n--\ninclude/linux/liveupdate.h=46=struct liveupdate_file_op_args {\ninclude/linux/liveupdate.h:47:\tstruct liveupdate_file_handler *handler;\ninclude/linux/liveupdate.h-48-\tint retrieve_status;\n--\ninclude/linux/liveupdate.h=74=struct liveupdate_file_ops {\ninclude/linux/liveupdate.h:75:\tbool (*can_preserve)(struct liveupdate_file_handler *handler,\ninclude/linux/liveupdate.h-76-\t\t\t     struct file *file);\n--\ninclude/linux/liveupdate.h-88-/**\ninclude/linux/liveupdate.h:89: * struct liveupdate_file_handler - Represents a handler for a live-updatable file type.\ninclude/linux/liveupdate.h-90- * @ops:                Callback functions\n--\ninclude/linux/liveupdate.h-100- */\ninclude/linux/liveupdate.h:101:struct liveupdate_file_handler {\ninclude/linux/liveupdate.h-102-\tconst struct liveupdate_file_ops *ops;\n--\ninclude/linux/liveupdate.h=232=int liveupdate_reboot(void);\ninclude/linux/liveupdate.h-233-\ninclude/linux/liveupdate.h:234:int liveupdate_register_file_handler(struct liveupdate_file_handler *fh);\ninclude/linux/liveupdate.h:235:void liveupdate_unregister_file_handler(struct liveupdate_file_handler *fh);\ninclude/linux/liveupdate.h-236-\ninclude/linux/liveupdate.h:237:int liveupdate_register_flb(struct liveupdate_file_handler *fh,\ninclude/linux/liveupdate.h-238-\t\t\t    struct liveupdate_flb *flb);\ninclude/linux/liveupdate.h:239:void liveupdate_unregister_flb(struct liveupdate_file_handler *fh,\ninclude/linux/liveupdate.h-240-\t\t\t       struct liveupdate_flb *flb);\n--\ninclude/linux/liveupdate.h=254=static inline int liveupdate_reboot(void)\n--\ninclude/linux/liveupdate.h-258-\ninclude/linux/liveupdate.h:259:static inline int liveupdate_register_file_handler(struct liveupdate_file_handler *fh)\ninclude/linux/liveupdate.h-260-{\n--\ninclude/linux/liveupdate.h-263-\ninclude/linux/liveupdate.h:264:static inline void liveupdate_unregister_file_handler(struct liveupdate_file_handler *fh)\ninclude/linux/liveupdate.h-265-{\n--\ninclude/linux/liveupdate.h-267-\ninclude/linux/liveupdate.h:268:static inline int liveupdate_register_flb(struct liveupdate_file_handler *fh,\ninclude/linux/liveupdate.h-269-\t\t\t\t\t  struct liveupdate_flb *flb)\n--\ninclude/linux/liveupdate.h-273-\ninclude/linux/liveupdate.h:274:static inline void liveupdate_unregister_flb(struct liveupdate_file_handler *fh,\ninclude/linux/liveupdate.h-275-\t\t\t\t\t     struct liveupdate_flb *flb)\n--\nkernel/liveupdate/luo_file.c-20- * Kernel modules responsible for a specific file type (e.g., memfd, vfio)\nkernel/liveupdate/luo_file.c:21: * register a \u0026struct liveupdate_file_handler. This handler provides a set of\nkernel/liveupdate/luo_file.c-22- * callbacks that LUO invokes at different stages of the update process, most\n--\nkernel/liveupdate/luo_file.c=119=static DEFINE_XARRAY(luo_preserved_files);\n--\nkernel/liveupdate/luo_file.c-122- * struct luo_file - Represents a single preserved file instance.\nkernel/liveupdate/luo_file.c:123: * @fh:            Pointer to the \u0026struct liveupdate_file_handler that manages\nkernel/liveupdate/luo_file.c-124- *                 this type of file.\n--\nkernel/liveupdate/luo_file.c=161=struct luo_file {\nkernel/liveupdate/luo_file.c:162:\tstruct liveupdate_file_handler *fh;\nkernel/liveupdate/luo_file.c-163-\tstruct file *file;\n--\nkernel/liveupdate/luo_file.c-171-\nkernel/liveupdate/luo_file.c:172:static unsigned long luo_get_id(struct liveupdate_file_handler *fh,\nkernel/liveupdate/luo_file.c-173-\t\t\t\tstruct file *file)\n--\nkernel/liveupdate/luo_file.c=230=int luo_preserve_file(struct luo_file_set *file_set, u64 token, int fd)\n--\nkernel/liveupdate/luo_file.c-232-\tstruct liveupdate_file_op_args args = {0};\nkernel/liveupdate/luo_file.c:233:\tstruct liveupdate_file_handler *fh;\nkernel/liveupdate/luo_file.c-234-\tstruct luo_file *luo_file;\n--\nkernel/liveupdate/luo_file.c=719=static int luo_file_deserialize_one(struct luo_file_set *file_set,\n--\nkernel/liveupdate/luo_file.c-721-{\nkernel/liveupdate/luo_file.c:722:\tstruct liveupdate_file_handler *fh;\nkernel/liveupdate/luo_file.c-723-\tbool handler_found = false;\n--\nkernel/liveupdate/luo_file.c=855=void luo_file_set_destroy(struct luo_file_set *file_set)\n--\nkernel/liveupdate/luo_file.c-863- * liveupdate_register_file_handler - Register a file handler with LUO.\nkernel/liveupdate/luo_file.c:864: * @fh: Pointer to a caller-allocated \u0026struct liveupdate_file_handler.\nkernel/liveupdate/luo_file.c-865- * The caller must initialize this structure, including a unique\n--\nkernel/liveupdate/luo_file.c-873- */\nkernel/liveupdate/luo_file.c:874:int liveupdate_register_file_handler(struct liveupdate_file_handler *fh)\nkernel/liveupdate/luo_file.c-875-{\nkernel/liveupdate/luo_file.c:876:\tstruct liveupdate_file_handler *fh_iter;\nkernel/liveupdate/luo_file.c-877-\tint err;\n--\nkernel/liveupdate/luo_file.c-919- */\nkernel/liveupdate/luo_file.c:920:void liveupdate_unregister_file_handler(struct liveupdate_file_handler *fh)\nkernel/liveupdate/luo_file.c-921-{\n--\nkernel/liveupdate/luo_flb.c=207=void liveupdate_flb_put_incoming(struct liveupdate_flb *flb)\n--\nkernel/liveupdate/luo_flb.c-248- */\nkernel/liveupdate/luo_flb.c:249:int luo_flb_file_preserve(struct liveupdate_file_handler *fh)\nkernel/liveupdate/luo_flb.c-250-{\n--\nkernel/liveupdate/luo_flb.c-284- */\nkernel/liveupdate/luo_flb.c:285:void luo_flb_file_unpreserve(struct liveupdate_file_handler *fh)\nkernel/liveupdate/luo_flb.c-286-{\n--\nkernel/liveupdate/luo_flb.c-305- */\nkernel/liveupdate/luo_flb.c:306:void luo_flb_file_finish(struct liveupdate_file_handler *fh)\nkernel/liveupdate/luo_flb.c-307-{\n--\nkernel/liveupdate/luo_flb.c-315-\nkernel/liveupdate/luo_flb.c:316:static void luo_flb_unregister_one(struct liveupdate_file_handler *fh,\nkernel/liveupdate/luo_flb.c-317-\t\t\t\t   struct liveupdate_flb *flb)\n--\nkernel/liveupdate/luo_flb.c-358- */\nkernel/liveupdate/luo_flb.c:359:void luo_flb_unregister_all(struct liveupdate_file_handler *fh)\nkernel/liveupdate/luo_flb.c-360-{\n--\nkernel/liveupdate/luo_flb.c-393- */\nkernel/liveupdate/luo_flb.c:394:int liveupdate_register_flb(struct liveupdate_file_handler *fh,\nkernel/liveupdate/luo_flb.c-395-\t\t\t    struct liveupdate_flb *flb)\n--\nkernel/liveupdate/luo_flb.c-473- */\nkernel/liveupdate/luo_flb.c:474:void liveupdate_unregister_flb(struct liveupdate_file_handler *fh,\nkernel/liveupdate/luo_flb.c-475-\t\t\t       struct liveupdate_flb *flb)\n--\nkernel/liveupdate/luo_internal.h=99=void luo_file_set_destroy(struct luo_file_set *file_set);\nkernel/liveupdate/luo_internal.h-100-\nkernel/liveupdate/luo_internal.h:101:int luo_flb_file_preserve(struct liveupdate_file_handler *fh);\nkernel/liveupdate/luo_internal.h:102:void luo_flb_file_unpreserve(struct liveupdate_file_handler *fh);\nkernel/liveupdate/luo_internal.h:103:void luo_flb_file_finish(struct liveupdate_file_handler *fh);\nkernel/liveupdate/luo_internal.h:104:void luo_flb_unregister_all(struct liveupdate_file_handler *fh);\nkernel/liveupdate/luo_internal.h-105-int __init luo_flb_setup_outgoing(u64 *flbs_pa);\n--\nkernel/liveupdate/luo_internal.h=107=void luo_flb_serialize(void);\n--\nkernel/liveupdate/luo_internal.h-109-#ifdef CONFIG_LIVEUPDATE_TEST\nkernel/liveupdate/luo_internal.h:110:void liveupdate_test_register(struct liveupdate_file_handler *fh);\nkernel/liveupdate/luo_internal.h-111-#else\nkernel/liveupdate/luo_internal.h:112:static inline void liveupdate_test_register(struct liveupdate_file_handler *fh) { }\nkernel/liveupdate/luo_internal.h-113-#endif\n--\nlib/tests/liveupdate.c=87=static void liveupdate_test_init(void)\n--\nlib/tests/liveupdate.c-114-\nlib/tests/liveupdate.c:115:void liveupdate_test_register(struct liveupdate_file_handler *fh)\nlib/tests/liveupdate.c-116-{\n--\nmm/memfd_luo.c=518=static int memfd_luo_retrieve(struct liveupdate_file_op_args *args)\n--\nmm/memfd_luo.c-579-\nmm/memfd_luo.c:580:static bool memfd_luo_can_preserve(struct liveupdate_file_handler *handler,\nmm/memfd_luo.c-581-\t\t\t\t   struct file *file)\n--\nmm/memfd_luo.c=593=static const struct liveupdate_file_ops memfd_luo_file_ops = {\n--\nmm/memfd_luo.c-603-\nmm/memfd_luo.c:604:static struct liveupdate_file_handler memfd_luo_handler = {\nmm/memfd_luo.c-605-\t.ops = \u0026memfd_luo_file_ops,\n"
}

gemini-3.1-pro-preview

null

null

							input: 28125
							output: 22
							thoughts: 208
						

**Analyzing the Live Update Feature's Implementation**

Okay, so I'm diving into this `CONFIG_LIVEUPDATE` feature, specifically the memfd-backed implementation, `memfd_luo`. The goal here is clearly to preserve files across a `kexec` transition. My focus is on understanding the interaction between this memfd backend and the file restoration process.

I see that the patch touches `kho_restore_folio` and `kho_restore_pages`. These routines are critical because they're directly used within `memfd_luo_retrieve_folios` and `kho_restore_vmalloc`. Hmm, hold on a second… these `kho_restore_*` functions are called *during* the retrieval phase. This retrieval phase is triggered when a file is brought back into memory via `memfd_luo_retrieve`.

The key question is, can a user space process directly call `memfd_luo_retrieve`?  I need to verify the call path. Let's see... looking at the code, `memfd_luo_retrieve` is called through `memfd_luo_file_ops.retrieve`.  This then points to the function  `luo_file_deserialize_one` or something similar, which will be the one that likely triggers the call. I need to understand that call chain thoroughly, as that is where a security vulnerability may lie. I'll need to check the parameters and data that are deserialized as part of this process. Let's dig deeper into `luo_file_deserialize_one`.

{
  "Expression": "luo_file_deserialize_one"
}

{
  "Output": "kernel/liveupdate/luo_file.c=680=int luo_file_finish(struct luo_file_set *file_set)\n--\nkernel/liveupdate/luo_file.c-718-\nkernel/liveupdate/luo_file.c:719:static int luo_file_deserialize_one(struct luo_file_set *file_set,\nkernel/liveupdate/luo_file.c-720-\t\t\t\t    struct luo_file_ser *ser)\n--\nkernel/liveupdate/luo_file.c=784=int luo_file_deserialize(struct luo_file_set *file_set,\n--\nkernel/liveupdate/luo_file.c-817-\twhile ((file_ser = kho_block_set_it_read_entry(\u0026it))) {\nkernel/liveupdate/luo_file.c:818:\t\terr = luo_file_deserialize_one(file_set, file_ser);\nkernel/liveupdate/luo_file.c-819-\t\tif (err)\n"
}

gemini-3.1-pro-preview

null

null

							input: 28964
							output: 20
							thoughts: 13
						

Here's my thought process, as if I were considering this function:

**Tracing the Call Stack for `luo_file_deserialize`**

Okay, so `luo_file_deserialize`... I need to figure out where that function is actually being *called* from. That's the crucial first step. I can't just operate in a vacuum. Where's it used? What parts of the system rely on it? Is there a clearly defined entry point, or is it buried deep within a nested module?

I need to quickly identify the places where `luo_file_deserialize` is invoked. I can't start optimizing it, refactoring it, or even fully *understanding* its role until I understand its context. Is this a top-level function in a critical path, or a utility function for a very specific task? The location of its calls will inform all of that. I'm thinking I'll need to use my IDE's search function and the cross-reference functionality to track down every instance. I'm looking for the immediate callers, but also considering the indirect paths that might lead to it.

{
  "Expression": "luo_file_deserialize"
}

{
  "Output": "kernel/liveupdate/luo_file.c-55- *\nkernel/liveupdate/luo_file.c:56: * 3. Deserialize: After kexec, luo_file_deserialize() runs when session gets\nkernel/liveupdate/luo_file.c-57- *    deserialized (which is when /dev/liveupdate is first opened). It reads the\n--\nkernel/liveupdate/luo_file.c=119=static DEFINE_XARRAY(luo_preserved_files);\n--\nkernel/liveupdate/luo_file.c-157- * during the .freeze() callback before being serialized for the next kernel.\nkernel/liveupdate/luo_file.c:158: * After reboot, these structures are recreated by luo_file_deserialize() and\nkernel/liveupdate/luo_file.c-159- * are finally cleaned up by luo_file_finish().\n--\nkernel/liveupdate/luo_file.c=680=int luo_file_finish(struct luo_file_set *file_set)\n--\nkernel/liveupdate/luo_file.c-718-\nkernel/liveupdate/luo_file.c:719:static int luo_file_deserialize_one(struct luo_file_set *file_set,\nkernel/liveupdate/luo_file.c-720-\t\t\t\t    struct luo_file_ser *ser)\n--\nkernel/liveupdate/luo_file.c-759-/**\nkernel/liveupdate/luo_file.c:760: * luo_file_deserialize - Reconstructs the list of preserved files in the new kernel.\nkernel/liveupdate/luo_file.c-761- * @file_set:     The incoming file_set to fill with deserialized data.\n--\nkernel/liveupdate/luo_file.c-783- */\nkernel/liveupdate/luo_file.c:784:int luo_file_deserialize(struct luo_file_set *file_set,\nkernel/liveupdate/luo_file.c-785-\t\t\t struct luo_file_set_ser *file_set_ser)\n--\nkernel/liveupdate/luo_file.c-817-\twhile ((file_ser = kho_block_set_it_read_entry(\u0026it))) {\nkernel/liveupdate/luo_file.c:818:\t\terr = luo_file_deserialize_one(file_set, file_ser);\nkernel/liveupdate/luo_file.c-819-\t\tif (err)\n--\nkernel/liveupdate/luo_internal.h=95=int luo_file_finish(struct luo_file_set *file_set);\nkernel/liveupdate/luo_internal.h:96:int luo_file_deserialize(struct luo_file_set *file_set,\nkernel/liveupdate/luo_internal.h-97-\t\t\t struct luo_file_set_ser *file_set_ser);\n--\nkernel/liveupdate/luo_session.c=551=static int luo_session_deserialize_one(struct luo_session_header *sh,\n--\nkernel/liveupdate/luo_session.c-572-\tscoped_guard(mutex, \u0026session-\u003emutex) {\nkernel/liveupdate/luo_session.c:573:\t\terr = luo_file_deserialize(\u0026session-\u003efile_set,\nkernel/liveupdate/luo_session.c-574-\t\t\t\t\t   \u0026ser-\u003efile_set_ser);\n"
}

gemini-3.1-pro-preview

null

null

							input: 30123
							output: 22
							thoughts: 73
						

Okay, let's break this down.

**Initial Impressions on Liveupdate and Deserialization**

Right, `luo_file_deserialize`. My initial thought is, that function is triggered when `/dev/liveupdate` is accessed for the first time, or if a session is being deserialized. That makes sense, a live update would need to deserialize something. Now, hang on a second... `luo_session_deserialize_one` is also called during boot, or when `/dev/liveupdate` is opened, is it not? That deserves further investigation. Let's start by looking into `luo_session_deserialize_one` - that seems like the key function to understand how these processes intertwine during initial startup and live update operations.

{
  "Expression": "luo_session_deserialize_one"
}

{
  "Output": "kernel/liveupdate/luo_session.c=535=int __init luo_session_setup_incoming(u64 sessions_pa)\n--\nkernel/liveupdate/luo_session.c-550-\nkernel/liveupdate/luo_session.c:551:static int luo_session_deserialize_one(struct luo_session_header *sh,\nkernel/liveupdate/luo_session.c-552-\t\t\t\t       struct luo_session_ser *ser)\n--\nkernel/liveupdate/luo_session.c=585=int luo_session_deserialize(void)\n--\nkernel/liveupdate/luo_session.c-618-\twhile ((ser = kho_block_set_it_read_entry(\u0026it))) {\nkernel/liveupdate/luo_session.c:619:\t\terr = luo_session_deserialize_one(sh, ser);\nkernel/liveupdate/luo_session.c-620-\t\tif (err)\n"
}

gemini-3.1-pro-preview

null

null

							input: 30635
							output: 20
							thoughts: 13
						

Here's a summary of my thought process, focusing on understanding the context of `luo_session_deserialize`:

**Understanding the Function's Origins**

Okay, so `luo_session_deserialize`. The first thing I'm doing is trying to pinpoint its invocation. Where *exactly* is this function being called from? Is it within the core session management module? Is it triggered by a specific event, perhaps a user login, a request for session data, or during application startup? Knowing the caller is critical to understanding its purpose and potential vulnerabilities. I need to trace the call stack to see where the call originates. Am I looking at code within the core framework, a third-party library, or something specific to this application? This will influence the assumptions I can make about the data being deserialized and the security implications. I'm going to need to dig into the codebase and find the references to the function.

{
  "Expression": "luo_session_deserialize"
}

{
  "Output": "kernel/liveupdate/luo_core.c=330=static int luo_open(struct inode *inodep, struct file *filep)\n--\nkernel/liveupdate/luo_core.c-339-\t/* Always return -EIO to user if deserialization fail */\nkernel/liveupdate/luo_core.c:340:\tif (luo_session_deserialize()) {\nkernel/liveupdate/luo_core.c-341-\t\tatomic_set(\u0026ldev-\u003ein_use, 0);\n--\nkernel/liveupdate/luo_internal.h=84=int luo_session_serialize(void);\nkernel/liveupdate/luo_internal.h:85:int luo_session_deserialize(void);\nkernel/liveupdate/luo_internal.h-86-\n--\nkernel/liveupdate/luo_session.c-41- *\nkernel/liveupdate/luo_session.c:42: * 3.  Deserialization (in new kernel): After kexec, `luo_session_deserialize()`\nkernel/liveupdate/luo_session.c-43- *     runs, reading the serialized data and creating a list of `struct\n--\nkernel/liveupdate/luo_session.c=535=int __init luo_session_setup_incoming(u64 sessions_pa)\n--\nkernel/liveupdate/luo_session.c-550-\nkernel/liveupdate/luo_session.c:551:static int luo_session_deserialize_one(struct luo_session_header *sh,\nkernel/liveupdate/luo_session.c-552-\t\t\t\t       struct luo_session_ser *ser)\n--\nkernel/liveupdate/luo_session.c-584-\nkernel/liveupdate/luo_session.c:585:int luo_session_deserialize(void)\nkernel/liveupdate/luo_session.c-586-{\n--\nkernel/liveupdate/luo_session.c-618-\twhile ((ser = kho_block_set_it_read_entry(\u0026it))) {\nkernel/liveupdate/luo_session.c:619:\t\terr = luo_session_deserialize_one(sh, ser);\nkernel/liveupdate/luo_session.c-620-\t\tif (err)\n"
}

gemini-3.1-pro-preview

null

null

							input: 31442
							output: 39
							thoughts: 143
						

**Analyzing the Live Update Mechanism**

Okay, so I'm tracing the path of `/dev/liveupdate` here. The entry point I'm seeing is `luo_open`, and that's the handler for the device. If syzkaller opens that device, it's going to hit `luo_session_deserialize`. Now, here's where it gets interesting, because `luo_session_deserialize` is *supposed* to handle KHO data that might be passed from a previous kernel – think `kexec` or a similar scenario. But, during a standard boot, without that KHO data, it's very likely `luo_session_deserialize` is going to either return zero or just quietly do nothing. I need to verify that; my next step is definitely to dive into the code of `luo_session_deserialize` itself and confirm this behavior. Gotta see exactly what that function does in the absence of KHO data.

{
  "File": "kernel/liveupdate/luo_session.c",
  "FirstLine": 585,
  "LineCount": 40
}

{
  "Contents": " 585:\tint luo_session_deserialize(void)\n 586:\t{\n 587:\t\tstruct luo_session_header *sh = \u0026luo_session_global.incoming;\n 588:\t\tstatic bool is_deserialized;\n 589:\t\tstruct luo_session_ser *ser;\n 590:\t\tstruct kho_block_set_it it;\n 591:\t\tstatic int saved_err;\n 592:\t\tint err;\n 593:\t\n 594:\t\t/* If has been deserialized, always return the same error code */\n 595:\t\tif (is_deserialized)\n 596:\t\t\treturn saved_err;\n 597:\t\n 598:\t\tis_deserialized = true;\n 599:\t\tif (!sh-\u003eactive)\n 600:\t\t\treturn 0;\n 601:\t\n 602:\t\t/*\n 603:\t\t * Note on error handling:\n 604:\t\t *\n 605:\t\t * If deserialization fails (e.g., allocation failure or corrupt data),\n 606:\t\t * we intentionally skip cleanup of sessions that were already restored.\n 607:\t\t *\n 608:\t\t * A partial failure leaves the preserved state inconsistent.\n 609:\t\t * Implementing a safe \"undo\" to unwind complex dependencies (sessions,\n 610:\t\t * files, hardware state) is error-prone and provides little value, as\n 611:\t\t * the system is effectively in a broken state.\n 612:\t\t *\n 613:\t\t * We treat these resources as leaked. The expected recovery path is for\n 614:\t\t * userspace to detect the failure and trigger a reboot, which will\n 615:\t\t * reliably reset devices and reclaim memory.\n 616:\t\t */\n 617:\t\tkho_block_set_it_init(\u0026it, \u0026sh-\u003eblock_set);\n 618:\t\twhile ((ser = kho_block_set_it_read_entry(\u0026it))) {\n 619:\t\t\terr = luo_session_deserialize_one(sh, ser);\n 620:\t\t\tif (err)\n 621:\t\t\t\tgoto save_err;\n 622:\t\t}\n 623:\t\n 624:\t\tkho_block_set_destroy(\u0026sh-\u003eblock_set);\n"
}

gemini-3.1-pro-preview

null

null

							input: 32437
							output: 39
							thoughts: 31
						

Okay, here's my interpretation of this logic, tailored as though I, a seasoned expert, am thinking it through:

**Checking Session Activity**

Alright, so the first thing I see is a very concise check: `!sh->active`. This immediately tells me we're looking at a critical guard condition. If this evaluates to true, the function instantly returns a zero value. No further processing occurs. I can infer that the function's purpose is likely tied to handling a "session" identified by `sh`. The `active` flag within that session structure, `sh`, is the key.

Then I see where the `active` flag gets set. It happens inside `luo_session_setup_incoming`. So, setting up an incoming session is what makes `sh->active` true. Any call to a method in the session that does not have an active session likely returns 0, indicating an error.

Essentially, this is a quick and efficient way to bail out if a session hasn't been properly initialized or activated, likely protecting against null pointer exceptions or unexpected behavior from using a session that isn't ready. Good defensive programming practice.

{
  "File": "kernel/liveupdate/luo_session.c",
  "FirstLine": 535,
  "LineCount": 20
}

{
  "Contents": " 535:\tint __init luo_session_setup_incoming(u64 sessions_pa)\n 536:\t{\n 537:\t\tstruct luo_session_header *sh = \u0026luo_session_global.incoming;\n 538:\t\tint err;\n 539:\t\n 540:\t\tif (!sessions_pa)\n 541:\t\t\treturn 0;\n 542:\t\n 543:\t\terr = kho_block_set_restore(\u0026sh-\u003eblock_set, sessions_pa);\n 544:\t\tif (err)\n 545:\t\t\treturn err;\n 546:\t\n 547:\t\tsh-\u003eactive = true;\n 548:\t\treturn 0;\n 549:\t}\n 550:\t\n 551:\tstatic int luo_session_deserialize_one(struct luo_session_header *sh,\n 552:\t\t\t\t\t       struct luo_session_ser *ser)\n 553:\t{\n 554:\t\tstruct luo_session *session;\n"
}

gemini-3.1-pro-preview

null

null

							input: 33034
							output: 35
							thoughts: 305
						

**Analyzing the Kernel Object Handover (KHO) Initialization and Restore Path**

Okay, so `luo_session_setup_incoming` is invoked on boot with `sessions_pa`, and if no KHO data exists, which is the norm for a fresh Syzkaller boot, `sessions_pa` is zero. That means `sh->active` stays false. Consequently, `luo_session_deserialize` does nothing, returning zero, and the entire restore mechanism is effectively bypassed. I need to figure out if there is a viable path to reach the preserve path at all.

Let's see… I should check `kho_preserve_page`. Looks like it's unused, that's a dead end. Okay, let's look at `kho_init_high_order_page`. Ah, it's called exclusively from `kho_init_folio` and `kho_restore_page`, and then `kho_init_folio` itself is only called from `kho_restore_folio`. Makes sense. Now `kho_restore_folio` is only triggered through `kho_restore_free`, `kho_test_restore_data`, and the `memfd_luo_discard_folios` and `memfd_luo_retrieve_folios` operations. All those are part of the restore path.

The crucial question is this: Can the restore path be entered if KHO data isn't present? No, it's impossible. Because either `kho_is_enabled()` will be false or `sh->active` will be false. So I need to dig deeper. I need to go over the edge cases and not assume a fresh boot.

Wait, the `test_kho` module! I need to re-examine `kho_test_init`.

{
  "File": "lib/test_kho.c",
  "FirstLine": 314,
  "LineCount": 30
}

{
  "Contents": " 314:\tstatic int __init kho_test_init(void)\n 315:\t{\n 316:\t\tphys_addr_t fdt_phys;\n 317:\t\tint err;\n 318:\t\n 319:\t\tif (!kho_is_enabled())\n 320:\t\t\treturn 0;\n 321:\t\n 322:\t\terr = kho_retrieve_subtree(KHO_TEST_FDT, \u0026fdt_phys, NULL);\n 323:\t\tif (!err) {\n 324:\t\t\terr = kho_test_restore(fdt_phys);\n 325:\t\t\tif (err)\n 326:\t\t\t\tpr_err(\"KHO restore failed\\n\");\n 327:\t\t\telse\n 328:\t\t\t\tpr_info(\"KHO restore succeeded\\n\");\n 329:\t\n 330:\t\t\treturn err;\n 331:\t\t}\n 332:\t\n 333:\t\tif (err != -ENOENT) {\n 334:\t\t\tpr_warn(\"failed to retrieve %s FDT: %d\\n\", KHO_TEST_FDT, err);\n 335:\t\t\treturn err;\n 336:\t\t}\n 337:\t\n 338:\t\treturn kho_test_save();\n 339:\t}\n 340:\tmodule_init(kho_test_init);\n 341:\t\n 342:\tstatic void kho_test_cleanup(void)\n 343:\t{\n"
}

gemini-3.1-pro-preview

null

null

							input: 34156
							output: 19
							thoughts: 60
						

Here's my take on the thought process:

**KHO Feature Logic Check**

Okay, so I'm looking at this piece of code. It looks like we're trying to figure out if the KHO feature is enabled. The core of this logic hinges on `kho_is_enabled()`. My immediate thought is, "Right, `kho_is_enabled()` acts as the gatekeeper here." If that function returns false, meaning KHO isn't enabled, then the entire section likely zeroes out whatever value it's dealing with. A quick check of `kho_is_enabled()` reveals that it verifies whether the kernel was booted with KHO data in order to make its determination. I should just confirm how that function is implemented and what factors make KHO enabled. Let's make sure I understand the conditional execution inside `kho_is_enabled()`. Need to double-check that part.

{
  "Expression": "kho_is_enabled"
}

{
  "Output": "include/linux/kexec_handover.h=17=struct page;\n--\ninclude/linux/kexec_handover.h-19-#ifdef CONFIG_KEXEC_HANDOVER\ninclude/linux/kexec_handover.h:20:bool kho_is_enabled(void);\ninclude/linux/kexec_handover.h-21-bool is_kho_boot(void);\n--\ninclude/linux/kexec_handover.h=44=void kho_populate(phys_addr_t fdt_phys, u64 fdt_len, phys_addr_t scratch_phys,\n--\ninclude/linux/kexec_handover.h-46-#else\ninclude/linux/kexec_handover.h:47:static inline bool kho_is_enabled(void)\ninclude/linux/kexec_handover.h-48-{\n--\nkernel/liveupdate/kexec_handover.c=58=static bool kho_enable __ro_after_init = IS_ENABLED(CONFIG_KEXEC_HANDOVER_ENABLE_DEFAULT);\nkernel/liveupdate/kexec_handover.c-59-\nkernel/liveupdate/kexec_handover.c:60:bool kho_is_enabled(void)\nkernel/liveupdate/kexec_handover.c-61-{\n--\nkernel/liveupdate/kexec_handover.c-63-}\nkernel/liveupdate/kexec_handover.c:64:EXPORT_SYMBOL_GPL(kho_is_enabled);\nkernel/liveupdate/kexec_handover.c-65-\n--\nkernel/liveupdate/luo_core.c=84=static int __init luo_early_startup(void)\n--\nkernel/liveupdate/luo_core.c-90-\nkernel/liveupdate/luo_core.c:91:\tif (!kho_is_enabled()) {\nkernel/liveupdate/luo_core.c-92-\t\tif (liveupdate_enabled())\n--\nlib/test_kho.c=314=static int __init kho_test_init(void)\n--\nlib/test_kho.c-318-\nlib/test_kho.c:319:\tif (!kho_is_enabled())\nlib/test_kho.c-320-\t\treturn 0;\n--\nmm/memblock.c=2616=static int __init reserve_mem_init(void)\n--\nmm/memblock.c-2619-\nmm/memblock.c:2620:\tif (!kho_is_enabled() || !reserved_mem_count)\nmm/memblock.c-2621-\t\treturn 0;\n"
}

gemini-3.1-pro-preview

null

null

							input: 35090
							output: 39
							thoughts: 13
						

Here's my take on those thoughts, tailored for an expert audience:

**Analyzing the `kho_is_enabled` Implementation**

Okay, so the mental gears are already turning. I need to take a look at the `kho_is_enabled` implementation. My initial concern is always around its potential impact on performance and maintainability, especially if this function is frequently called or deeply nested within critical paths. I'm already thinking about potential bottlenecks – is it checking a static variable, querying a database, or performing more complex logic? I need to quickly identify its dependencies and its intended purpose within the broader system. I also need to think about the possible side effects, especially if it modifies any shared state. Are there any known issues associated with it in our existing code base? I'm anticipating that it's probably written by someone else, so I want to get an overview of its potential vulnerabilities. Is there a chance of any race conditions? I'll probably start by grepping for its usage throughout the codebase to understand its scope and context. Time to dig in and understand this function.

{
  "File": "kernel/liveupdate/kexec_handover.c",
  "FirstLine": 58,
  "LineCount": 10
}

{
  "Contents": "  58:\tstatic bool kho_enable __ro_after_init = IS_ENABLED(CONFIG_KEXEC_HANDOVER_ENABLE_DEFAULT);\n  59:\t\n  60:\tbool kho_is_enabled(void)\n  61:\t{\n  62:\t\treturn kho_enable;\n  63:\t}\n  64:\tEXPORT_SYMBOL_GPL(kho_is_enabled);\n  65:\t\n  66:\tstatic int __init kho_parse_enable(char *p)\n  67:\t{\n"
}

gemini-3.1-pro-preview

null

null

							input: 35513
							output: 35
							thoughts: 75
						

**Analyzing the Kexec Handover Enable Logic**

Okay, so I'm looking at this `kho_is_enabled` function and it's pretty straightforward. It simply returns the value of `kho_enable`. Which, as I see it, defaults to `CONFIG_KEXEC_HANDOVER_ENABLE_DEFAULT`. So essentially, if the configuration option `CONFIG_KEXEC_HANDOVER_ENABLE_DEFAULT` is set to true, then `kho_is_enabled()` will return true. That's good. Now, to be sure, I need to check `test_kho.c` again.

{
  "File": "lib/test_kho.c",
  "FirstLine": 314,
  "LineCount": 30
}

{
  "Contents": " 314:\tstatic int __init kho_test_init(void)\n 315:\t{\n 316:\t\tphys_addr_t fdt_phys;\n 317:\t\tint err;\n 318:\t\n 319:\t\tif (!kho_is_enabled())\n 320:\t\t\treturn 0;\n 321:\t\n 322:\t\terr = kho_retrieve_subtree(KHO_TEST_FDT, \u0026fdt_phys, NULL);\n 323:\t\tif (!err) {\n 324:\t\t\terr = kho_test_restore(fdt_phys);\n 325:\t\t\tif (err)\n 326:\t\t\t\tpr_err(\"KHO restore failed\\n\");\n 327:\t\t\telse\n 328:\t\t\t\tpr_info(\"KHO restore succeeded\\n\");\n 329:\t\n 330:\t\t\treturn err;\n 331:\t\t}\n 332:\t\n 333:\t\tif (err != -ENOENT) {\n 334:\t\t\tpr_warn(\"failed to retrieve %s FDT: %d\\n\", KHO_TEST_FDT, err);\n 335:\t\t\treturn err;\n 336:\t\t}\n 337:\t\n 338:\t\treturn kho_test_save();\n 339:\t}\n 340:\tmodule_init(kho_test_init);\n 341:\t\n 342:\tstatic void kho_test_cleanup(void)\n 343:\t{\n"
}

gemini-3.1-pro-preview

null

null

							input: 36156
							output: 35
							thoughts: 69
						

**Analyzing the KHO Data Retrieval Process**

Okay, so the code's operating under a conditional. If `kho_is_enabled()` returns true, that triggers a call to `kho_retrieve_subtree`. My immediate thought is, what's the expected behavior if there's *no* KHO data available? Aha, the text says `kho_retrieve_subtree` will return `-ENOENT`. That makes sense; a standard error code to indicate "no such entity." Now, after that retrieval (or lack thereof), the code jumps to `kho_test_save()`. I need to understand what this `kho_test_save()` function is doing in this context. It's the critical next step in understanding the complete flow. I'll need to dig into its implementation to see how it reacts to or incorporates the result (or lack thereof) from `kho_retrieve_subtree`.

{
  "File": "lib/test_kho.c",
  "FirstLine": 276,
  "LineCount": 40
}

{
  "Contents": " 276:\t\t\tfolio_put(folio);\n 277:\t\t}\n 278:\t\n 279:\t\tvfree(folios_info);\n 280:\t\n 281:\t\tif (csum != *old_csum)\n 282:\t\t\treturn -EINVAL;\n 283:\t\n 284:\t\treturn 0;\n 285:\t}\n 286:\t\n 287:\tstatic int kho_test_restore(phys_addr_t fdt_phys)\n 288:\t{\n 289:\t\tvoid *fdt = phys_to_virt(fdt_phys);\n 290:\t\tconst unsigned int *magic;\n 291:\t\tint node, len, err;\n 292:\t\n 293:\t\tnode = fdt_path_offset(fdt, \"/\");\n 294:\t\tif (node \u003c 0)\n 295:\t\t\treturn -EINVAL;\n 296:\t\n 297:\t\tif (fdt_node_check_compatible(fdt, node, KHO_TEST_COMPAT))\n 298:\t\t\treturn -EINVAL;\n 299:\t\n 300:\t\tmagic = fdt_getprop(fdt, node, \"magic\", \u0026len);\n 301:\t\tif (!magic || len != sizeof(*magic))\n 302:\t\t\treturn -EINVAL;\n 303:\t\n 304:\t\tif (*magic != KHO_TEST_MAGIC)\n 305:\t\t\treturn -EINVAL;\n 306:\t\n 307:\t\terr = kho_test_restore_data(fdt, node);\n 308:\t\tif (err)\n 309:\t\t\treturn err;\n 310:\t\n 311:\t\treturn 0;\n 312:\t}\n 313:\t\n 314:\tstatic int __init kho_test_init(void)\n 315:\t{\n"
}

gemini-3.1-pro-preview

null

null

							input: 36970
							output: 19
							thoughts: 13
						

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

**Analyzing the Workflow: `kho_test_save`**

Okay, first things first, I need to get my head back in the game and re-orient myself. That `kho_test_save` file... it's a critical piece, and I need to review it. It probably contains the crucial state information or data manipulation steps that I was working on. I need to understand exactly where I left off. Is it a checkpoint save? A test configuration? Or something else entirely? I should know. I’ll be looking for any clues that jump out about that previous testing iteration, or about the architecture as a whole. Time to dive in and get up to speed.

{
  "Expression": "kho_test_save"
}

{
  "Output": "lib/test_kho.c=162=static int kho_test_generate_data(struct kho_test_state *state)\n--\nlib/test_kho.c-204-\nlib/test_kho.c:205:static int kho_test_save(void)\nlib/test_kho.c-206-{\n--\nlib/test_kho.c=314=static int __init kho_test_init(void)\n--\nlib/test_kho.c-337-\nlib/test_kho.c:338:\treturn kho_test_save();\nlib/test_kho.c-339-}\n"
}

gemini-3.1-pro-preview

null

null

							input: 37333
							output: 35
							thoughts: 11
						

Okay, here's my interpretation of that thought process, tailored for an expert audience, and written in the first person:

**Analyzing the Data Set: kho\_test\_save**

Alright, the next step is to examine this file, `kho_test_save`. Immediately, I’m thinking about what assumptions I can make about its contents based on the naming convention. "kho" might suggest a particular data format or source – perhaps a specific research group's output, a particular experiment, or a specific type of data encoding. "test" indicates it's likely a temporary or developmental file, maybe a validation or preliminary output. And "save" tells me this is probably a snapshot of the data at a certain point, a checkpoint in the workflow. I need to keep in mind, of course, that these are just initial clues. I have to resist the urge to jump to conclusions until I've actually looked at the file itself. Now, I need to figure out how to parse this appropriately. Is this a custom binary format? Is it text-based, like CSV, JSON, or XML? Or is it something a bit more esoteric? The first priority is to determine how to read the data, so that I can figure out its structure and then start analyzing it.

{
  "File": "lib/test_kho.c",
  "FirstLine": 205,
  "LineCount": 30
}

{
  "Contents": " 205:\tstatic int kho_test_save(void)\n 206:\t{\n 207:\t\tstruct kho_test_state *state = \u0026kho_test_state;\n 208:\t\tstruct folio **folios;\n 209:\t\tunsigned long max_nr;\n 210:\t\tint err;\n 211:\t\n 212:\t\tmax_mem = PAGE_ALIGN(max_mem);\n 213:\t\tmax_nr = max_mem \u003e\u003e PAGE_SHIFT;\n 214:\t\n 215:\t\tfolios = kvmalloc_objs(*state-\u003efolios, max_nr);\n 216:\t\tif (!folios)\n 217:\t\t\treturn -ENOMEM;\n 218:\t\tstate-\u003efolios = folios;\n 219:\t\n 220:\t\terr = kho_test_generate_data(state);\n 221:\t\tif (err)\n 222:\t\t\tgoto err_free_folios;\n 223:\t\n 224:\t\terr = kho_test_preserve(state);\n 225:\t\tif (err)\n 226:\t\t\tgoto err_free_folios;\n 227:\t\n 228:\t\treturn 0;\n 229:\t\n 230:\terr_free_folios:\n 231:\t\tkvfree(folios);\n 232:\t\treturn err;\n 233:\t}\n 234:\t\n"
}

gemini-3.1-pro-preview

null

null

							input: 38027
							output: 19
							thoughts: 15
						

Okay, here's my interpretation of that process, thinking as the code itself might:

**The Preservation Dance: A Look at Data Handling**

Alright, so `kho_test_save` is initiating a critical operation. It's essentially saying, "Hey, before I do something potentially risky, I need to make sure the data is safe and sound." The code is specifically calling `kho_test_preserve`. That's a clear signal to me that `kho_test_save`'s functionality, whatever it might be, depends on a preliminary data safeguarding step. This looks like a common pattern, and a good one! It's likely that `kho_test_preserve` does some kind of backup, snapshotting, serialization, or versioning. I'm inferring, with my expert eye, that the system is engineered to prioritize data integrity.

{
  "Expression": "kho_test_preserve"
}

{
  "Output": "lib/test_kho.c=45=static void kho_test_unpreserve_data(struct kho_test_state *state)\n--\nlib/test_kho.c-53-\nlib/test_kho.c:54:static int kho_test_preserve_data(struct kho_test_state *state)\nlib/test_kho.c-55-{\n--\nlib/test_kho.c=97=static int kho_test_prepare_fdt(struct kho_test_state *state, ssize_t fdt_size)\n--\nlib/test_kho.c-123-\nlib/test_kho.c:124:static int kho_test_preserve(struct kho_test_state *state)\nlib/test_kho.c-125-{\n--\nlib/test_kho.c-137-\nlib/test_kho.c:138:\terr = kho_test_preserve_data(state);\nlib/test_kho.c-139-\tif (err)\n--\nlib/test_kho.c=205=static int kho_test_save(void)\n--\nlib/test_kho.c-223-\nlib/test_kho.c:224:\terr = kho_test_preserve(state);\nlib/test_kho.c-225-\tif (err)\n"
}

gemini-3.1-pro-preview

null

null

							input: 38584
							output: 34
							thoughts: 13
						

Okay, let's dive into this. Here's my take on processing this task, focusing on what I'd be thinking as a seasoned expert:

**Analyzing the Task: `kho_test_preserve_data`**

Alright, the file or test suite I need to look at is named `kho_test_preserve_data`. Immediately, a few things jump out. The name suggests a specific focus on *data preservation*. This is key. We're not just running tests, we're making sure data integrity is maintained, potentially during some kind of operation or process. "Kho" is a prefix I haven't seen before, I'll need to figure out what that signifies; it might be a specific library, project, or context. My initial mental model is that this is a test designed to confirm that some operation, maybe a data migration, a system update, or a specific data transformation, doesn't inadvertently lead to data loss or corruption. I'll be looking for asserts that focus on data structures, checksums, data sizes, or specific data values before and after the action being tested. My focus will be on the edge cases, where things are most likely to go wrong, like concurrency issues, error handling, or unusual data inputs. I'll need to assess the test's scope – does it cover the entire data set, or is it sampling specific key areas? Is the testing environment clearly defined? This is crucial for replication and reliability of results. Is there documentation accompanying this test? That would be fantastic! The goal is to figure out whether the test is sufficient to validate this data preservation process.

{
  "File": "lib/test_kho.c",
  "FirstLine": 54,
  "LineCount": 40
}

{
  "Contents": "  54:\tstatic int kho_test_preserve_data(struct kho_test_state *state)\n  55:\t{\n  56:\t\tstruct kho_vmalloc folios_info_phys;\n  57:\t\tphys_addr_t *folios_info;\n  58:\t\tint err;\n  59:\t\n  60:\t\tfolios_info = vmalloc_array(state-\u003enr_folios, sizeof(*folios_info));\n  61:\t\tif (!folios_info)\n  62:\t\t\treturn -ENOMEM;\n  63:\t\n  64:\t\terr = kho_preserve_vmalloc(folios_info, \u0026folios_info_phys);\n  65:\t\tif (err)\n  66:\t\t\tgoto err_free_info;\n  67:\t\n  68:\t\tstate-\u003efolios_info_phys = folios_info_phys;\n  69:\t\tstate-\u003efolios_info = folios_info;\n  70:\t\n  71:\t\tfor (int i = 0; i \u003c state-\u003enr_folios; i++) {\n  72:\t\t\tstruct folio *folio = state-\u003efolios[i];\n  73:\t\t\tunsigned int order = folio_order(folio);\n  74:\t\n  75:\t\t\tfolios_info[i] = virt_to_phys(folio_address(folio)) | order;\n  76:\t\t\terr = kho_preserve_folio(folio);\n  77:\t\t\tif (err)\n  78:\t\t\t\tgoto err_unpreserve;\n  79:\t\t\tstate-\u003enr_folios_preserved++;\n  80:\t\t}\n  81:\t\n  82:\t\treturn 0;\n  83:\t\n  84:\terr_unpreserve:\n  85:\t\t/*\n  86:\t\t * kho_test_unpreserve_data frees folio_info, bail out immediately to\n  87:\t\t * avoid double free\n  88:\t\t */\n  89:\t\tkho_test_unpreserve_data(state);\n  90:\t\treturn err;\n  91:\t\n  92:\terr_free_info:\n  93:\t\tvfree(folios_info);\n"
}

gemini-3.1-pro-preview

null

null

							input: 39508
							output: 19
							thoughts: 538
						

**Analyzing the KHO Data Preservation Code**

Okay, let's break this down. `kho_test_preserve_data` calls `kho_preserve_folio`, but not `kho_preserve_page`.  That immediately makes me wonder why `kho_preserve_page` exists at all. It appears completely unused, unless... wait, what about `kho_preserve_pages`? I remember it being used within `kho_preserve_vmalloc`.

Now, if I recall correctly, `kho_preserve_vmalloc` *is* called by `kho_test_preserve_data`. And `kho_test_save()` is called at module load if KHO is not enabled, which is the default for a normal boot. So `kho_preserve_pages` is reachable via `kho_test_save()` as long as KHO is disabled.

Hold on, if `kho_is_enabled()` is false, `kho_test_init()` should return 0. Let me just quickly confirm that by looking at the code for `kho_test_init()`.

```c
static int __init kho_test_init(void)
{
	phys_addr_t fdt_phys;
	int err;

	if (!kho_is_enabled())
		return 0;

	err = kho_retrieve_subtree(KHO_TEST_FDT, &fdt_phys, NULL);
	if (!err) {
		err = kho_test_restore(fdt_phys);
		if (err)
			pr_err("KHO restore failed\n");
		else
			pr_info("KHO restore succeeded\n");

		return err;
	}

	if (err != -ENOENT) {
		pr_warn("failed to retrieve %s FDT: %d\n", KHO_TEST_FDT, err);
		return err;
	}

	return kho_test_save();
}
```

Okay, yes, I was right. If `!kho_is_enabled()`, the function returns 0. So, now it is clear: `kho_test_save()` is *only* called if `kho_is_enabled()` is TRUE, *and* `kho_retrieve_subtree` returns `-ENOENT`. That's the critical condition here.

So, when *is* `kho_is_enabled()` true? Ah, it's true if `CONFIG_KEXEC_HANDOVER_ENABLE_DEFAULT` is set, or if the user specifically passes `kho=on` on the kernel command line. Got it. So, if KHO is supposed to be enabled, but we are doing a normal boot (i.e., there is no KHO data), `kho_retrieve_subtree` *will* return `-ENOENT`. And then, `kho_test_save()` *will* be called.

Now, let me just quickly refresh my memory on the workings of `kho_retrieve_subtree`...

{
  "Expression": "kho_retrieve_subtree"
}

{
  "Output": "include/linux/kexec_handover.h=39=void kho_remove_subtree(void *blob);\ninclude/linux/kexec_handover.h:40:int kho_retrieve_subtree(const char *name, phys_addr_t *phys, size_t *size);\ninclude/linux/kexec_handover.h-41-\n--\ninclude/linux/kexec_handover.h=115=static inline void kho_remove_subtree(void *blob) { }\ninclude/linux/kexec_handover.h-116-\ninclude/linux/kexec_handover.h:117:static inline int kho_retrieve_subtree(const char *name, phys_addr_t *phys,\ninclude/linux/kexec_handover.h-118-\t\t\t\t       size_t *size)\n--\nkernel/liveupdate/kexec_handover.c=1435=EXPORT_SYMBOL_GPL(is_kho_boot);\n--\nkernel/liveupdate/kexec_handover.c-1437-/**\nkernel/liveupdate/kexec_handover.c:1438: * kho_retrieve_subtree - retrieve a preserved sub blob by its name.\nkernel/liveupdate/kexec_handover.c-1439- * @name: the name of the sub blob passed to kho_add_subtree().\n--\nkernel/liveupdate/kexec_handover.c-1447- */\nkernel/liveupdate/kexec_handover.c:1448:int kho_retrieve_subtree(const char *name, phys_addr_t *phys, size_t *size)\nkernel/liveupdate/kexec_handover.c-1449-{\n--\nkernel/liveupdate/kexec_handover.c-1481-}\nkernel/liveupdate/kexec_handover.c:1482:EXPORT_SYMBOL_GPL(kho_retrieve_subtree);\nkernel/liveupdate/kexec_handover.c-1483-\n--\nkernel/liveupdate/kexec_handover.c=1530=static void __init kho_in_kexec_metadata(void)\n--\nkernel/liveupdate/kexec_handover.c-1536-\nkernel/liveupdate/kexec_handover.c:1537:\terr = kho_retrieve_subtree(KHO_METADATA_NODE_NAME, \u0026metadata_phys,\nkernel/liveupdate/kexec_handover.c-1538-\t\t\t\t   \u0026blob_size);\n--\nkernel/liveupdate/luo_core.c=84=static int __init luo_early_startup(void)\n--\nkernel/liveupdate/luo_core.c-98-\t/* Retrieve LUO state from KHO. */\nkernel/liveupdate/luo_core.c:99:\terr = kho_retrieve_subtree(LUO_KHO_ENTRY_NAME, \u0026luo_ser_phys, \u0026len);\nkernel/liveupdate/luo_core.c-100-\tif (err) {\n--\nlib/test_kho.c=314=static int __init kho_test_init(void)\n--\nlib/test_kho.c-321-\nlib/test_kho.c:322:\terr = kho_retrieve_subtree(KHO_TEST_FDT, \u0026fdt_phys, NULL);\nlib/test_kho.c-323-\tif (!err) {\n--\nmm/memblock.c=2630=static void *__init reserve_mem_kho_retrieve_fdt(void)\n--\nmm/memblock.c-2638-\nmm/memblock.c:2639:\terr = kho_retrieve_subtree(MEMBLOCK_KHO_FDT, \u0026fdt_phys, NULL);\nmm/memblock.c-2640-\tif (err) {\n"
}

gemini-3.1-pro-preview

null

null

							input: 41676
							output: 23
							thoughts: 428
						

**Analyzing the KHO Data Flow**

Okay, let me break this down. If `kho_is_enabled()` is on and `kho_retrieve_subtree` fails with an `-ENOENT` error, then `kho_test_save()` gets called. `kho_test_save()` seems to trigger a cascade of function calls: `kho_test_generate_data()`, `kho_test_preserve()`, which in turn calls `kho_test_preserve_data()`. Then this leads to `kho_preserve_vmalloc()` and `kho_preserve_folio()`. Eventually, `kho_preserve_vmalloc()` calls `kho_preserve_pages()`. So, under the right configuration (`CONFIG_KEXEC_HANDOVER_ENABLE_DEFAULT=y` and `CONFIG_TEST_KEXEC_HANDOVER=y`), `kho_preserve_pages` should be reachable during boot.

But wait a minute! I'm seeing `kho_preserve_page` (singular) added in the patch. And those functions, `kho_preserve_page`, `kho_unpreserve_page`, and `kho_restore_page`, are completely unused in the current tree! That's strange. The only *usable* changes in the patch seem to be the refactoring, which utilizes `__kho_restore_page` within `kho_restore_folio` and `kho_restore_pages`. Plus, there's the addition of `clear_page_tag_ref(page + i)` in `kho_init_high_order_page`.

However, the bigger issue is that `kho_restore_folio` and `kho_restore_pages` are *only* called during the restore phase. The restore phase is *only* triggered if `kho_retrieve_subtree` succeeds.  `kho_retrieve_subtree` can only succeed if there's KHO data passed from a previous kernel. And syzkaller, based on my understanding, doesn't actually perform kexec with KHO data. It starts with a fresh VM image. That means the entire restore phase is unreachable in a standard syzkaller setup!

Hmm, is there any way to possibly trigger `kho_restore_folio` from user space somehow? Maybe `memfd_luo_retrieve_folios`? I should probably check that...

{
  "Expression": "memfd_luo_retrieve_folios"
}

{
  "Output": "mm/memfd_luo.c=387=static void memfd_luo_finish(struct liveupdate_file_op_args *args)\n--\nmm/memfd_luo.c-416-\nmm/memfd_luo.c:417:static int memfd_luo_retrieve_folios(struct file *file,\nmm/memfd_luo.c-418-\t\t\t\t     struct memfd_luo_folio_ser *folios_ser,\n--\nmm/memfd_luo.c=518=static int memfd_luo_retrieve(struct liveupdate_file_op_args *args)\n--\nmm/memfd_luo.c-561-\nmm/memfd_luo.c:562:\t\terr = memfd_luo_retrieve_folios(file, folios_ser, ser-\u003enr_folios);\nmm/memfd_luo.c-563-\t\tvfree(folios_ser);\n"
}

gemini-3.1-pro-preview

null

null

							input: 42871
							output: 21
							thoughts: 470
						

**Analysis of the Unreachable Code Path**

Okay, let me break this down. `memfd_luo_retrieve` is buried pretty deep, called through a chain of functions: `luo_file_deserialize_one`, `luo_file_deserialize`, `luo_session_deserialize_one`, `luo_session_deserialize`, and finally, initiated by a call to `luo_open` on `/dev/liveupdate`.  The critical point is that `luo_session_deserialize` immediately returns if a flag, `sh->active`, is false.

This `sh->active` flag is only set in `luo_session_setup_incoming`, which, I now recall, is called during boot with `sessions_pa`. If, and this is the crux of the issue, there is *no* KHO data, `sessions_pa` is zero, and that crucial `sh->active` flag stays false. That means the whole deserialization process is short-circuited – `luo_session_deserialize` does nothing. Consequently, `memfd_luo_retrieve` is *never* called, and therefore all the functions *downstream* from it, including `kho_restore_folio`, `__kho_restore_page`, and `kho_init_high_order_page`, are also inaccessible.

The patch itself appears to introduce:
1.  Unused functions: `kho_preserve_page`, `kho_unpreserve_page`, and `kho_restore_page`.
2.  Refactoring that, again, depends on that inaccessible deserialization path.
3.  Some `clear_page_tag_ref` calls within the initialization logic, also unreachable.

Given that a standard syzkaller environment, which doesn't boot with KHO data, will never reach any of these modified or added functions, it seems that there's no point in fuzzing this patch as it stands.

Hold on, though. I need to be completely sure. Syzkaller is capable of clever tricks.  Can it write something to `/sys/kernel/kexec_handover` or similar to inject KHO data into the system, potentially making this code path accessible?  I should check the available debugfs or sysfs interfaces to see if there's any mechanism to inject that data directly. If there is, then we *might* have a target.

no matches

{
  "Expression": "kho_session_setup_incoming"
}

{
  "error": "no matches"
}

gemini-3.1-pro-preview

null

null

							input: 43888
							output: 22
							thoughts: 14
						

Okay, here's my interpretation of that thought process, assuming I'm deeply familiar with code and debugging, especially in a network or session-related context:

**Analyzing `luo_session_setup_incoming`**

Alright, that's where we're starting. "Let's check `luo_session_setup_incoming`." This indicates a specific, likely crucial, piece of code related to incoming sessions. My initial thought process is geared towards understanding its role and potential issues. I'm probably facing a problem with incoming sessions, and this is where I've decided to start my investigation. It could be anything from a connection problem, authentication failure, or data handling issue. Knowing the name suggests this specific function handles the initial setup of an incoming communication session, a pivotal point where things can go right or, more often in my line of work, terribly wrong. I'll need to rapidly recall or locate the code for this function and start mentally tracing the execution flow. My goal is to quickly pinpoint any logical flaws, potential race conditions, or obvious errors in the implementation. This initial check is a critical first step.

{
  "Expression": "luo_session_setup_incoming"
}

{
  "Output": "kernel/liveupdate/luo_core.c=84=static int __init luo_early_startup(void)\n--\nkernel/liveupdate/luo_core.c-124-\nkernel/liveupdate/luo_core.c:125:\terr = luo_session_setup_incoming(luo_ser-\u003esessions_pa);\nkernel/liveupdate/luo_core.c-126-\tif (err)\n--\nkernel/liveupdate/luo_internal.h=82=void __init luo_session_setup_outgoing(u64 *sessions_pa);\nkernel/liveupdate/luo_internal.h:83:int __init luo_session_setup_incoming(u64 sessions_pa);\nkernel/liveupdate/luo_internal.h-84-int luo_session_serialize(void);\n--\nkernel/liveupdate/luo_session.c=529=void __init luo_session_setup_outgoing(u64 *sessions_pa)\n--\nkernel/liveupdate/luo_session.c-534-\nkernel/liveupdate/luo_session.c:535:int __init luo_session_setup_incoming(u64 sessions_pa)\nkernel/liveupdate/luo_session.c-536-{\n"
}

gemini-3.1-pro-preview

null

null

							input: 44491
							output: 19
							thoughts: 274
						

**My Assessment of the Patch Series**

Okay, so this patch series... I see it's called from `luo_early_startup`. Right, and `luo_early_startup` is triggered during the boot process. That means it's inherently dependent on the KHO data, specifically `luo_ser_phys`, which it gets via `kho_retrieve_subtree`. This data is passed from the bootloader or potentially the previous kernel. There's no way to inject anything from userspace after boot – it's all pre-boot configuration.

Now, my task is to decide if this needs fuzzing. The instructions are clear: I *must* examine the code itself, not rely on what I *think* I know. Fine. Let's look into this `kho_preserve_page` function. The documentation says to consider it, so I checked. Initially, I found it's *not* used anywhere in the kernel source. The changes appear limited to adding unused functions and refactoring unreachable code. So, on the surface, it looks like there are no functional changes to be fuzzed.

However, I'm going to double check and make sure that `kho_preserve_page` isn't lurking in some macro definition or something that could potentially make it relevant. This is a thorough review, after all, and I need to be certain. I'll make sure there's no hidden usage before I reach a final conclusion. After my check, I'll return `WorthFuzzing=false`.

{
  "Expression": "kho_preserve_page"
}

{
  "Output": "include/linux/kexec_handover.h=24=void kho_unpreserve_folio(struct folio *folio);\ninclude/linux/kexec_handover.h:25:int kho_preserve_page(struct page *page, unsigned int order);\ninclude/linux/kexec_handover.h-26-void kho_unpreserve_page(struct page *page, unsigned int order);\ninclude/linux/kexec_handover.h:27:int kho_preserve_pages(struct page *page, unsigned long nr_pages);\ninclude/linux/kexec_handover.h-28-void kho_unpreserve_pages(struct page *page, unsigned long nr_pages);\n--\ninclude/linux/kexec_handover.h=62=static inline void kho_unpreserve_folio(struct folio *folio) { }\ninclude/linux/kexec_handover.h-63-\ninclude/linux/kexec_handover.h:64:static inline int kho_preserve_pages(struct page *page, unsigned int nr_pages)\ninclude/linux/kexec_handover.h-65-{\n--\ninclude/linux/kexec_handover.h=69=static inline void kho_unpreserve_pages(struct page *page, unsigned int nr_pages) { }\ninclude/linux/kexec_handover.h-70-\ninclude/linux/kexec_handover.h:71:static inline int kho_preserve_page(struct page *page, unsigned int order)\ninclude/linux/kexec_handover.h-72-{\n--\nkernel/liveupdate/kexec_handover.c=441=EXPORT_SYMBOL_GPL(kho_restore_folio);\n--\nkernel/liveupdate/kexec_handover.c-447- * Restore a high-order page block that was preserved with\nkernel/liveupdate/kexec_handover.c:448: * kho_preserve_page().\nkernel/liveupdate/kexec_handover.c-449- *\n--\nkernel/liveupdate/kexec_handover.c=464=EXPORT_SYMBOL_GPL(kho_restore_page);\n--\nkernel/liveupdate/kexec_handover.c-471- * Restore a contiguous list of order 0 pages that was preserved with\nkernel/liveupdate/kexec_handover.c:472: * kho_preserve_pages().\nkernel/liveupdate/kexec_handover.c-473- *\n--\nkernel/liveupdate/kexec_handover.c=919=EXPORT_SYMBOL_GPL(kho_unpreserve_folio);\n--\nkernel/liveupdate/kexec_handover.c-921-/**\nkernel/liveupdate/kexec_handover.c:922: * kho_preserve_page - preserve a high-order page block.\nkernel/liveupdate/kexec_handover.c-923- * @page: head page of the block.\n--\nkernel/liveupdate/kexec_handover.c-932- * perform the split, and then re-preserve the individual pages using\nkernel/liveupdate/kexec_handover.c:933: * kho_preserve_pages().\nkernel/liveupdate/kexec_handover.c-934- *\n--\nkernel/liveupdate/kexec_handover.c-936- */\nkernel/liveupdate/kexec_handover.c:937:int kho_preserve_page(struct page *page, unsigned int order)\nkernel/liveupdate/kexec_handover.c-938-{\n--\nkernel/liveupdate/kexec_handover.c-946-}\nkernel/liveupdate/kexec_handover.c:947:EXPORT_SYMBOL_GPL(kho_preserve_page);\nkernel/liveupdate/kexec_handover.c-948-\n--\nkernel/liveupdate/kexec_handover.c-954- * Instructs KHO to unpreserve a high-order block that was preserved by\nkernel/liveupdate/kexec_handover.c:955: * kho_preserve_page() before.\nkernel/liveupdate/kexec_handover.c-956- */\n--\nkernel/liveupdate/kexec_handover.c=964=EXPORT_SYMBOL_GPL(kho_unpreserve_page);\nkernel/liveupdate/kexec_handover.c-965-\nkernel/liveupdate/kexec_handover.c:966:static unsigned int __kho_preserve_pages_order(unsigned long start_pfn,\nkernel/liveupdate/kexec_handover.c-967-\t\t\t\t\t       unsigned long end_pfn)\n--\nkernel/liveupdate/kexec_handover.c=983=static void __kho_unpreserve(struct kho_radix_tree *tree,\n--\nkernel/liveupdate/kexec_handover.c-988-\twhile (pfn \u003c end_pfn) {\nkernel/liveupdate/kexec_handover.c:989:\t\torder = __kho_preserve_pages_order(pfn, end_pfn);\nkernel/liveupdate/kexec_handover.c-990-\n--\nkernel/liveupdate/kexec_handover.c-997-/**\nkernel/liveupdate/kexec_handover.c:998: * kho_preserve_pages - preserve contiguous pages across kexec\nkernel/liveupdate/kexec_handover.c-999- * @page: first page in the list.\n--\nkernel/liveupdate/kexec_handover.c-1007- */\nkernel/liveupdate/kexec_handover.c:1008:int kho_preserve_pages(struct page *page, unsigned long nr_pages)\nkernel/liveupdate/kexec_handover.c-1009-{\n--\nkernel/liveupdate/kexec_handover.c-1022-\twhile (pfn \u003c end_pfn) {\nkernel/liveupdate/kexec_handover.c:1023:\t\tunsigned int order = __kho_preserve_pages_order(pfn, end_pfn);\nkernel/liveupdate/kexec_handover.c-1024-\n--\nkernel/liveupdate/kexec_handover.c-1038-}\nkernel/liveupdate/kexec_handover.c:1039:EXPORT_SYMBOL_GPL(kho_preserve_pages);\nkernel/liveupdate/kexec_handover.c-1040-\n--\nkernel/liveupdate/kexec_handover.c-1047- * This must be called with the same @page and @nr_pages as the corresponding\nkernel/liveupdate/kexec_handover.c:1048: * kho_preserve_pages() call. Unpreserving arbitrary sub-ranges of larger\nkernel/liveupdate/kexec_handover.c-1049- * preserved blocks is not supported.\n--\nkernel/liveupdate/kexec_handover.c=1092=static struct kho_vmalloc_chunk *new_vmalloc_chunk(struct kho_vmalloc_chunk *cur)\n--\nkernel/liveupdate/kexec_handover.c-1100-\nkernel/liveupdate/kexec_handover.c:1101:\terr = kho_preserve_pages(virt_to_page(chunk), 1);\nkernel/liveupdate/kexec_handover.c-1102-\tif (err)\n--\nkernel/liveupdate/kexec_handover.c=1142=int kho_preserve_vmalloc(void *ptr, struct kho_vmalloc *preservation)\n--\nkernel/liveupdate/kexec_handover.c-1167-\nkernel/liveupdate/kexec_handover.c:1168:\t\terr = kho_preserve_pages(vm-\u003epages[i], nr_contig_pages);\nkernel/liveupdate/kexec_handover.c-1169-\t\tif (err)\n--\nmm/memblock.c=2528=static int __init reserved_mem_preserve(void)\n--\nmm/memblock.c-2537-\nmm/memblock.c:2538:\t\terr = kho_preserve_pages(page, nr_pages);\nmm/memblock.c-2539-\t\tif (err)\n--\nmm/memblock.c=2557=static int __init prepare_kho_fdt(void)\n--\nmm/memblock.c-2569-\tfdt = page_to_virt(fdt_page);\nmm/memblock.c:2570:\terr = kho_preserve_pages(fdt_page, 1);\nmm/memblock.c-2571-\tif (err)\n"
}

gemini-3.1-pro-preview

null

null

							input: 47253
							output: 194
							thoughts: 41
						

**Unused Code and WorthFuzzing=False**

Okay, so I've taken a look at `kho_preserve_page` and, as I suspected, it's completely unused. Digging deeper, it's clear the only changes associated with it consist of unused functions and code that's fundamentally unreachable without any KHO data in play. Considering the effort to value ratio, and knowing that I'm dealing with code that essentially does nothing in the current context, I'm confident in setting `WorthFuzzing` to `false`. There's no value in further investigation or fuzzing efforts on this particular element, at least not in its present state.

{
  "EnableConfigs": [],
  "FocusSymbols": [],
  "Reasoning": "The patch introduces new APIs (`kho_preserve_page`, `kho_unpreserve_page`, `kho_restore_page`) for Kexec Handover (KHO) which are currently unused anywhere in the kernel tree. It also refactors `kho_restore_folio` and `kho_restore_pages` to use a new internal helper `__kho_restore_page`, and modifies `kho_init_high_order_page` to clear page tags for tail pages. However, all of these modified code paths are only reachable during the KHO restore phase, which strictly requires the kernel to be booted with KHO data passed from a previous kernel. Since syzkaller boots from a fresh VM image without KHO data, this code is completely unreachable in a standard fuzzing environment.",
  "WorthFuzzing": false
}

{
  "EnableConfigs": null,
  "FocusSymbols": [],
  "Reasoning": "The patch introduces new APIs (`kho_preserve_page`, `kho_unpreserve_page`, `kho_restore_page`) for Kexec Handover (KHO) which are currently unused anywhere in the kernel tree. It also refactors `kho_restore_folio` and `kho_restore_pages` to use a new internal helper `__kho_restore_page`, and modifies `kho_init_high_order_page` to clear page tags for tail pages. However, all of these modified code paths are only reachable during the KHO restore phase, which strictly requires the kernel to be booted with KHO data passed from a previous kernel. Since syzkaller boots from a fresh VM image without KHO data, this code is completely unreachable in a standard fuzzing environment.",
  "WorthFuzzing": false
}