From: Vlastimil Babka <vbabka@xxxxxxx>
Subject: mm, slub: restore the original intention of prefetch_freepointer()
In SLUB, prefetch_freepointer() is used when allocating an object from
cache's freelist, to make sure the next object in the list is cache-hot,
since it's probable it will be allocated soon.
Commit 2482ddec670f ("mm: add SLUB free list pointer obfuscation") has
unintentionally changed the prefetch in a way where the prefetch is turned
to a real fetch, and only the next->next pointer is prefetched. In case
there is not a stream of allocations that would benefit from prefetching,
the extra real fetch might add a useless cache miss to the allocation.
Restore the previous behavior.
Link: http://lkml.kernel.org/r/20180809085245.22448-1-vbabka@xxxxxxx
Fixes: 2482ddec670f ("mm: add SLUB free list pointer obfuscation")
Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
Acked-by: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Daniel Micay <danielmicay@xxxxxxxxx>
Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Pekka Enberg <penberg@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/slub.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
--- a/mm/slub.c~mm-slub-restore-the-original-intention-of-prefetch_freepointer
+++ a/mm/slub.c
@@ -271,8 +271,7 @@ static inline void *get_freepointer(stru
static void prefetch_freepointer(const struct kmem_cache *s, void *object)
{
- if (object)
- prefetch(freelist_dereference(s, object + s->offset));
+ prefetch(object + s->offset);
}
static inline void *get_freepointer_safe(struct kmem_cache *s, void *object)
_
