[RFC 2/7] mm: add page consistency checker header

[Sasha Levin <sashal@kernel.org>]

From: Sasha Levin <sashal@nvidia.com>

Define the interface for CONFIG_DEBUG_PAGE_CONSISTENCY. The API mirrors
the pattern used by page_table_check: inline wrapper functions check a
static key before calling the out-of-line tracking implementation, so
that callers in the allocator hot path only pay for a predicted-not-taken
branch when the feature is built in but not active.

The header is kept separate from the implementation so the hooks in
page_alloc.c can be added without pulling in implementation details.

Based-on-patch-by: Sanif Veeras <sveeras@nvidia.com>
Assisted-by: Claude:claude-opus-4-7 <noreply@anthropic.com>
Signed-off-by: Sasha Levin <sashal@nvidia.com>
---
 include/linux/page_consistency.h | 84 ++++++++++++++++++++++++++++++++
 1 file changed, 84 insertions(+)
 create mode 100644 include/linux/page_consistency.h

diff --git a/include/linux/page_consistency.h b/include/linux/page_consistency.h
new file mode 100644
index 000000000000..f335fa3d6c5d
--- /dev/null
+++ b/include/linux/page_consistency.h
@@ -0,0 +1,84 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Dual-bitmap page consistency checking
+ *
+ * Provides corruption detection for page allocations using complementary
+ * bitmaps where the invariant (primary == ~secondary) must hold.
+ *
+ * Based on NVIDIA safety research.
+ */
+#ifndef _LINUX_PAGE_CONSISTENCY_H
+#define _LINUX_PAGE_CONSISTENCY_H
+
+#include <linux/types.h>
+#include <linux/mm_types.h>
+
+/* Return codes for page consistency checking */
+enum page_consistency_result {
+	PAGE_CONSISTENCY_OK = 0,
+	PAGE_CONSISTENCY_MISMATCH,
+	PAGE_CONSISTENCY_NOT_TRACKED,
+};
+
+#ifdef CONFIG_DEBUG_PAGE_CONSISTENCY
+
+#include <linux/jump_label.h>
+DECLARE_STATIC_KEY_FALSE(page_consistency_enabled);
+
+/* Initialization - called during mm_core_init() */
+void __init page_consistency_init(void);
+
+/* Core tracking functions */
+void __page_consistency_alloc(struct page *page, unsigned int order);
+void __page_consistency_free(struct page *page, unsigned int order);
+
+/* Validation functions */
+enum page_consistency_result page_consistency_check_page(struct page *page);
+enum page_consistency_result page_consistency_validate_all(void);
+
+/**
+ * page_consistency_alloc - Track page allocation
+ * @page: Allocated page
+ * @order: Allocation order
+ *
+ * Called from post_alloc_hook() to track page allocations.
+ * The static key avoids the out-of-line tracking call until initialization.
+ */
+static inline void page_consistency_alloc(struct page *page, unsigned int order)
+{
+	if (static_branch_unlikely(&page_consistency_enabled))
+		__page_consistency_alloc(page, order);
+}
+
+/**
+ * page_consistency_free - Track page free
+ * @page: Page being freed
+ * @order: Free order
+ *
+ * Called from free_pages_prepare() to track page frees.
+ * The static key avoids the out-of-line tracking call until initialization.
+ */
+static inline void page_consistency_free(struct page *page, unsigned int order)
+{
+	if (static_branch_unlikely(&page_consistency_enabled))
+		__page_consistency_free(page, order);
+}
+
+#else /* !CONFIG_DEBUG_PAGE_CONSISTENCY */
+
+static inline void __init page_consistency_init(void) {}
+static inline void page_consistency_alloc(struct page *page, unsigned int order) {}
+static inline void page_consistency_free(struct page *page, unsigned int order) {}
+
+static inline enum page_consistency_result page_consistency_check_page(struct page *page)
+{
+	return PAGE_CONSISTENCY_OK;
+}
+
+static inline enum page_consistency_result page_consistency_validate_all(void)
+{
+	return PAGE_CONSISTENCY_OK;
+}
+
+#endif /* CONFIG_DEBUG_PAGE_CONSISTENCY */
+#endif /* _LINUX_PAGE_CONSISTENCY_H */
-- 
2.53.0