On Tue, Nov 10, 2020 at 11:20PM +0100, Andrey Konovalov wrote: > The reason cache merging is disabled with KASAN is because KASAN puts its > metadata right after the allocated object. When the merged caches have > slightly different sizes, the metadata ends up in different places, which > KASAN doesn't support. > > It might be possible to adjust the metadata allocation algorithm and make > it friendly to the cache merging code. Instead this change takes a simpler > approach and allows merging caches when no metadata is present. Which is > the case for hardware tag-based KASAN with kasan.mode=prod. > > Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx> > Link: https://linux-review.googlesource.com/id/Ia114847dfb2244f297d2cb82d592bf6a07455dba > --- > include/linux/kasan.h | 26 ++++++++++++++++++++++++-- > mm/kasan/common.c | 11 +++++++++++ > mm/slab_common.c | 11 ++++++++--- > 3 files changed, 43 insertions(+), 5 deletions(-) > > diff --git a/include/linux/kasan.h b/include/linux/kasan.h > index 534ab3e2935a..c754eca356f7 100644 > --- a/include/linux/kasan.h > +++ b/include/linux/kasan.h > @@ -81,17 +81,35 @@ struct kasan_cache { > }; > > #ifdef CONFIG_KASAN_HW_TAGS > + > DECLARE_STATIC_KEY_FALSE(kasan_flag_enabled); > + > static inline kasan_enabled(void) > { > return static_branch_likely(&kasan_flag_enabled); > } > -#else > + > +slab_flags_t __kasan_never_merge(slab_flags_t flags); > +static inline slab_flags_t kasan_never_merge(slab_flags_t flags) > +{ > + if (kasan_enabled()) > + return __kasan_never_merge(flags); > + return flags; > +} > + > +#else /* CONFIG_KASAN_HW_TAGS */ > + > static inline kasan_enabled(void) > { > return true; > } > -#endif > + > +static inline slab_flags_t kasan_never_merge(slab_flags_t flags) > +{ > + return flags; > +} > + > +#endif /* CONFIG_KASAN_HW_TAGS */ > > void __kasan_alloc_pages(struct page *page, unsigned int order); > static inline void kasan_alloc_pages(struct page *page, unsigned int order) > @@ -240,6 +258,10 @@ static inline kasan_enabled(void) > { > return false; > } > +static inline slab_flags_t kasan_never_merge(slab_flags_t flags) > +{ > + return flags; > +} > 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_cache_create(struct kmem_cache *cache, > diff --git a/mm/kasan/common.c b/mm/kasan/common.c > index 940b42231069..25b18c145b06 100644 > --- a/mm/kasan/common.c > +++ b/mm/kasan/common.c > @@ -81,6 +81,17 @@ asmlinkage void kasan_unpoison_task_stack_below(const void *watermark) > } > #endif /* CONFIG_KASAN_STACK */ > > +/* > + * Only allow cache merging when stack collection is disabled and no metadata > + * is present. > + */ > +slab_flags_t __kasan_never_merge(slab_flags_t flags) > +{ > + if (kasan_stack_collection_enabled()) > + return flags; > + return flags & ~SLAB_KASAN; > +} > + > void __kasan_alloc_pages(struct page *page, unsigned int order) > { > u8 tag; > diff --git a/mm/slab_common.c b/mm/slab_common.c > index f1b0c4a22f08..3042ee8ea9ce 100644 > --- a/mm/slab_common.c > +++ b/mm/slab_common.c > @@ -18,6 +18,7 @@ > #include <linux/seq_file.h> > #include <linux/proc_fs.h> > #include <linux/debugfs.h> > +#include <linux/kasan.h> > #include <asm/cacheflush.h> > #include <asm/tlbflush.h> > #include <asm/page.h> > @@ -49,12 +50,16 @@ static DECLARE_WORK(slab_caches_to_rcu_destroy_work, > slab_caches_to_rcu_destroy_workfn); > > /* > - * Set of flags that will prevent slab merging > + * Set of flags that will prevent slab merging. > + * Use slab_never_merge() instead. > */ > #define SLAB_NEVER_MERGE (SLAB_RED_ZONE | SLAB_POISON | SLAB_STORE_USER | \ > SLAB_TRACE | SLAB_TYPESAFE_BY_RCU | SLAB_NOLEAKTRACE | \ > SLAB_FAILSLAB | SLAB_KASAN) Rather than changing this to require using slab_never_merge() which removes SLAB_KASAN, could we not just have a function kasan_never_merge() that returns KASAN-specific flags that should never result in merging -- because as-is now, making kasan_never_merge() remove the SLAB_KASAN flag seems the wrong way around. Could we not just do this: #define SLAB_NEVER_MERGE (SLAB_RED_ZONE | SLAB_POISON | SLAB_STORE_USER | \ SLAB_TRACE | SLAB_TYPESAFE_BY_RCU | SLAB_NOLEAKTRACE | \ SLAB_FAILSLAB | kasan_never_merge()) ?? Of course that might be problematic if this always needs to be a compile-time constant, but currently that's not a requirement. > +/* KASAN allows merging in some configurations and will remove SLAB_KASAN. */ > +#define slab_never_merge() (kasan_never_merge(SLAB_NEVER_MERGE)) Braces unnecessary. > #define SLAB_MERGE_SAME (SLAB_RECLAIM_ACCOUNT | SLAB_CACHE_DMA | \ > SLAB_CACHE_DMA32 | SLAB_ACCOUNT) > > @@ -164,7 +169,7 @@ static unsigned int calculate_alignment(slab_flags_t flags, > */ > int slab_unmergeable(struct kmem_cache *s) > { > - if (slab_nomerge || (s->flags & SLAB_NEVER_MERGE)) > + if (slab_nomerge || (s->flags & slab_never_merge())) > return 1; > > if (s->ctor) > @@ -198,7 +203,7 @@ struct kmem_cache *find_mergeable(unsigned int size, unsigned int align, > size = ALIGN(size, align); > flags = kmem_cache_flags(size, flags, name, NULL); > > - if (flags & SLAB_NEVER_MERGE) > + if (flags & slab_never_merge()) > return NULL; > > list_for_each_entry_reverse(s, &slab_caches, list) { > -- > 2.29.2.222.g5d2a92d10f8-goog >
