[PATCH v2 3/3] mm, slab, kasan: replace kasan_never_merge() with SLAB_NO_MERGE

[Vlastimil Babka]

The SLAB_KASAN flag prevents merging of caches in some configurations,
which is handled in a rather complicated way via kasan_never_merge().
Since we now have a generic SLAB_NO_MERGE flag, we can instead use it
for KASAN caches in addition to SLAB_KASAN in those configurations,
and simplify the SLAB_NEVER_MERGE handling.

Tested-by: Xiongwei Song <xiongwei.song@xxxxxxxxxxxxx>
Reviewed-by: Chengming Zhou <chengming.zhou@xxxxxxxxx>
Reviewed-by: Andrey Konovalov <andreyknvl@xxxxxxxxx>
Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
---
 include/linux/kasan.h |  6 ------
 mm/kasan/generic.c    | 22 ++++++----------------
 mm/slab_common.c      |  2 +-
 3 files changed, 7 insertions(+), 23 deletions(-)

diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index dbb06d789e74..70d6a8f6e25d 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -429,7 +429,6 @@ struct kasan_cache {
 };
 
 size_t kasan_metadata_size(struct kmem_cache *cache, bool in_object);
-slab_flags_t kasan_never_merge(void);
 void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
 			slab_flags_t *flags);
 
@@ -446,11 +445,6 @@ static inline size_t kasan_metadata_size(struct kmem_cache *cache,
 {
 	return 0;
 }
-/* And thus nothing prevents cache merging. */
-static inline slab_flags_t kasan_never_merge(void)
-{
-	return 0;
-}
 /* And no cache-related metadata initialization is required. */
 static inline void kasan_cache_create(struct kmem_cache *cache,
 				      unsigned int *size,
diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
index df6627f62402..27297dc4a55b 100644
--- a/mm/kasan/generic.c
+++ b/mm/kasan/generic.c
@@ -334,14 +334,6 @@ DEFINE_ASAN_SET_SHADOW(f3);
 DEFINE_ASAN_SET_SHADOW(f5);
 DEFINE_ASAN_SET_SHADOW(f8);
 
-/* Only allow cache merging when no per-object metadata is present. */
-slab_flags_t kasan_never_merge(void)
-{
-	if (!kasan_requires_meta())
-		return 0;
-	return SLAB_KASAN;
-}
-
 /*
  * Adaptive redzone policy taken from the userspace AddressSanitizer runtime.
  * For larger allocations larger redzones are used.
@@ -370,15 +362,13 @@ void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
 		return;
 
 	/*
-	 * SLAB_KASAN is used to mark caches that are sanitized by KASAN
-	 * and that thus have per-object metadata.
-	 * Currently this flag is used in two places:
-	 * 1. In slab_ksize() to account for per-object metadata when
-	 *    calculating the size of the accessible memory within the object.
-	 * 2. In slab_common.c via kasan_never_merge() to prevent merging of
-	 *    caches with per-object metadata.
+	 * SLAB_KASAN is used to mark caches that are sanitized by KASAN and
+	 * that thus have per-object metadata. Currently, this flag is used in
+	 * slab_ksize() to account for per-object metadata when calculating the
+	 * size of the accessible memory within the object. Additionally, we use
+	 * SLAB_NO_MERGE to prevent merging of caches with per-object metadata.
 	 */
-	*flags |= SLAB_KASAN;
+	*flags |= SLAB_KASAN | SLAB_NO_MERGE;
 
 	ok_size = *size;
 
diff --git a/mm/slab_common.c b/mm/slab_common.c
index 238293b1dbe1..7cfa2f1ce655 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -50,7 +50,7 @@ static DECLARE_WORK(slab_caches_to_rcu_destroy_work,
  */
 #define SLAB_NEVER_MERGE (SLAB_RED_ZONE | SLAB_POISON | SLAB_STORE_USER | \
 		SLAB_TRACE | SLAB_TYPESAFE_BY_RCU | SLAB_NOLEAKTRACE | \
-		SLAB_FAILSLAB | SLAB_NO_MERGE | kasan_never_merge())
+		SLAB_FAILSLAB | SLAB_NO_MERGE)
 
 #define SLAB_MERGE_SAME (SLAB_RECLAIM_ACCOUNT | SLAB_CACHE_DMA | \
 			 SLAB_CACHE_DMA32 | SLAB_ACCOUNT)

-- 
2.43.2