Re: [PATCH 3/5] kasan, mm: integrate page_alloc init with HW_TAGS

This change uses the previously added memory initialization feature
of HW_TAGS KASAN routines for page_alloc memory when init_on_alloc/free
is enabled.

With this change, kernel_init_free_pages() is no longer called when
both HW_TAGS KASAN and init_on_alloc/free are enabled. Instead, memory
is initialized in KASAN runtime.

To avoid discrepancies with which memory gets initialized that can be
caused by future changes, both KASAN and kernel_init_free_pages() hooks
are put together and a warning comment is added.

This patch changes the order in which memory initialization and page
poisoning hooks are called. This doesn't lead to any side-effects, as
whenever page poisoning is enabled, memory initialization gets disabled.

Combining setting allocation tags with memory initialization improves
HW_TAGS KASAN performance when init_on_alloc/free is enabled.

Signed-off-by: Andrey Konovalov <redacted>
---
 include/linux/kasan.h | 16 ++++++++--------
 mm/kasan/common.c     |  8 ++++----
 mm/mempool.c          |  4 ++--
 mm/page_alloc.c       | 37 ++++++++++++++++++++++++++-----------
 4 files changed, 40 insertions(+), 25 deletions(-)

diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index 1d89b8175027..4c0f414a893b 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h

@@ -120,20 +120,20 @@ static __always_inline void kasan_unpoison_range(const void *addr, size_t size)
 		__kasan_unpoison_range(addr, size);
 }
 
-void __kasan_alloc_pages(struct page *page, unsigned int order);
+void __kasan_alloc_pages(struct page *page, unsigned int order, bool init);
 static __always_inline void kasan_alloc_pages(struct page *page,
-						unsigned int order)
+						unsigned int order, bool init)
 {
 	if (kasan_enabled())
-		__kasan_alloc_pages(page, order);
+		__kasan_alloc_pages(page, order, init);
 }
 
-void __kasan_free_pages(struct page *page, unsigned int order);
+void __kasan_free_pages(struct page *page, unsigned int order, bool init);
 static __always_inline void kasan_free_pages(struct page *page,
-						unsigned int order)
+						unsigned int order, bool init)
 {
 	if (kasan_enabled())
-		__kasan_free_pages(page, order);
+		__kasan_free_pages(page, order, init);
 }
 
 void __kasan_cache_create(struct kmem_cache *cache, unsigned int *size,

@@ -282,8 +282,8 @@ static inline slab_flags_t kasan_never_merge(void)
 	return 0;
 }
 static inline void kasan_unpoison_range(const void *address, size_t size) {}
-static inline void kasan_alloc_pages(struct page *page, unsigned int order) {}
-static inline void kasan_free_pages(struct page *page, unsigned int order) {}
+static inline void kasan_alloc_pages(struct page *page, unsigned int order, bool init) {}
+static inline void kasan_free_pages(struct page *page, unsigned int order, bool init) {}
 static inline void kasan_cache_create(struct kmem_cache *cache,
 				      unsigned int *size,
 				      slab_flags_t *flags) {}

diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 316f7f8cd8e6..6107c795611f 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c

@@ -97,7 +97,7 @@ slab_flags_t __kasan_never_merge(void)
 	return 0;
 }
 
-void __kasan_alloc_pages(struct page *page, unsigned int order)
+void __kasan_alloc_pages(struct page *page, unsigned int order, bool init)
 {
 	u8 tag;
 	unsigned long i;

@@ -108,14 +108,14 @@ void __kasan_alloc_pages(struct page *page, unsigned int order)
 	tag = kasan_random_tag();
 	for (i = 0; i < (1 << order); i++)
 		page_kasan_tag_set(page + i, tag);
-	kasan_unpoison(page_address(page), PAGE_SIZE << order, false);
+	kasan_unpoison(page_address(page), PAGE_SIZE << order, init);
 }
 
-void __kasan_free_pages(struct page *page, unsigned int order)
+void __kasan_free_pages(struct page *page, unsigned int order, bool init)
 {
 	if (likely(!PageHighMem(page)))
 		kasan_poison(page_address(page), PAGE_SIZE << order,
-			     KASAN_FREE_PAGE, false);
+			     KASAN_FREE_PAGE, init);
 }
 
 /*

diff --git a/mm/mempool.c b/mm/mempool.c
index 79959fac27d7..fe19d290a301 100644
--- a/mm/mempool.c
+++ b/mm/mempool.c

@@ -106,7 +106,7 @@ static __always_inline void kasan_poison_element(mempool_t *pool, void *element)
 	if (pool->alloc == mempool_alloc_slab || pool->alloc == mempool_kmalloc)
 		kasan_slab_free_mempool(element);
 	else if (pool->alloc == mempool_alloc_pages)
-		kasan_free_pages(element, (unsigned long)pool->pool_data);
+		kasan_free_pages(element, (unsigned long)pool->pool_data, false);
 }
 
 static void kasan_unpoison_element(mempool_t *pool, void *element)

@@ -114,7 +114,7 @@ static void kasan_unpoison_element(mempool_t *pool, void *element)
 	if (pool->alloc == mempool_alloc_slab || pool->alloc == mempool_kmalloc)
 		kasan_unpoison_range(element, __ksize(element));
 	else if (pool->alloc == mempool_alloc_pages)
-		kasan_alloc_pages(element, (unsigned long)pool->pool_data);
+		kasan_alloc_pages(element, (unsigned long)pool->pool_data, false);
 }
 
 static __always_inline void add_element(mempool_t *pool, void *element)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 0efb07b5907c..175bdb36d113 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c

@@ -396,14 +396,14 @@ static DEFINE_STATIC_KEY_TRUE(deferred_pages);
  * initialization is done, but this is not likely to happen.
  */
 static inline void kasan_free_nondeferred_pages(struct page *page, int order,
-							fpi_t fpi_flags)
+						bool init, fpi_t fpi_flags)
 {
 	if (static_branch_unlikely(&deferred_pages))
 		return;
 	if (!IS_ENABLED(CONFIG_KASAN_GENERIC) &&
 			(fpi_flags & FPI_SKIP_KASAN_POISON))
 		return;
-	kasan_free_pages(page, order);
+	kasan_free_pages(page, order, init);
 }
 
 /* Returns true if the struct page for the pfn is uninitialised */

@@ -455,12 +455,12 @@ defer_init(int nid, unsigned long pfn, unsigned long end_pfn)
 }
 #else
 static inline void kasan_free_nondeferred_pages(struct page *page, int order,
-							fpi_t fpi_flags)
+						bool init, fpi_t fpi_flags)
 {
 	if (!IS_ENABLED(CONFIG_KASAN_GENERIC) &&
 			(fpi_flags & FPI_SKIP_KASAN_POISON))
 		return;
-	kasan_free_pages(page, order);
+	kasan_free_pages(page, order, init);
 }
 
 static inline bool early_page_uninitialised(unsigned long pfn)

@@ -1242,6 +1242,7 @@ static __always_inline bool free_pages_prepare(struct page *page,
 			unsigned int order, bool check_free, fpi_t fpi_flags)
 {
 	int bad = 0;
+	bool init;
 
 	VM_BUG_ON_PAGE(PageTail(page), page);
 

@@ -1299,16 +1300,21 @@ static __always_inline bool free_pages_prepare(struct page *page,
 		debug_check_no_obj_freed(page_address(page),
 					   PAGE_SIZE << order);
 	}
-	if (want_init_on_free())
-		kernel_init_free_pages(page, 1 << order);
 
 	kernel_poison_pages(page, 1 << order);
 
 	/*
+	 * As memory initialization is integrated with hardware tag-based
+	 * KASAN, kasan_free_pages and kernel_init_free_pages must be
+	 * kept together to avoid discrepancies in behavior.
+	 *
 	 * With hardware tag-based KASAN, memory tags must be set before the
 	 * page becomes unavailable via debug_pagealloc or arch_free_page.
 	 */
-	kasan_free_nondeferred_pages(page, order, fpi_flags);
+	init = want_init_on_free();
+	if (init && !IS_ENABLED(CONFIG_KASAN_HW_TAGS))