Re: [PATCH 11/12] kasan: always inline HW_TAGS helper functions
From: Marco Elver <elver@google.com>
Date: 2021-02-03 15:53:30
Also in:
linux-arm-kernel, lkml
On Mon, Feb 01, 2021 at 08:43PM +0100, Andrey Konovalov wrote:
Mark all static functions in common.c and kasan.h that are used for hardware tag-based KASAN as __always_inline to avoid unnecessary function calls. Signed-off-by: Andrey Konovalov <redacted>
Does objtool complain about any of these? I'm not sure this is unconditionally a good idea. If there isn't a quantifiable performance bug or case where we cannot call a function, perhaps we can just let the compiler decide? More comments below.
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--- mm/kasan/common.c | 13 +++++++------ mm/kasan/kasan.h | 6 +++--- 2 files changed, 10 insertions(+), 9 deletions(-)diff --git a/mm/kasan/common.c b/mm/kasan/common.c index 5691cca69397..2004ecd6e43c 100644 --- a/mm/kasan/common.c +++ b/mm/kasan/common.c@@ -279,7 +279,8 @@ void __kasan_poison_object_data(struct kmem_cache *cache, void *object) * based on objects indexes, so that objects that are next to each other * get different tags. */ -static u8 assign_tag(struct kmem_cache *cache, const void *object, bool init) +static __always_inline u8 assign_tag(struct kmem_cache *cache, + const void *object, bool init)
This function might be small enough that it's fine.
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{ if (IS_ENABLED(CONFIG_KASAN_GENERIC)) return 0xff;@@ -321,8 +322,8 @@ void * __must_check __kasan_init_slab_obj(struct kmem_cache *cache, return (void *)object; } -static bool ____kasan_slab_free(struct kmem_cache *cache, void *object, - unsigned long ip, bool quarantine) +static __always_inline bool ____kasan_slab_free(struct kmem_cache *cache, + void *object, unsigned long ip, bool quarantine) {
Because ____kasan_slab_free() is tail-called by __kasan_slab_free() and __kasan_slab_free_mempool(), there should never be a call (and if there is we need to figure out why). The additional code-bloat and I-cache pressure might be worse vs. just a jump. I'd let the compiler decide.
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u8 tag; void *tagged_object;@@ -366,7 +367,7 @@ bool __kasan_slab_free(struct kmem_cache *cache, void *object, unsigned long ip) return ____kasan_slab_free(cache, object, ip, true); } -static bool ____kasan_kfree_large(void *ptr, unsigned long ip) +static __always_inline bool ____kasan_kfree_large(void *ptr, unsigned long ip) {
This one is tail-called by __kasan_kfree_large(). The usage in __kasan_slab_free_mempool() is in an unlikely branch.
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if (ptr != page_address(virt_to_head_page(ptr))) { kasan_report_invalid_free(ptr, ip);@@ -461,8 +462,8 @@ void * __must_check __kasan_slab_alloc(struct kmem_cache *cache, return tagged_object; } -static void *____kasan_kmalloc(struct kmem_cache *cache, const void *object, - size_t size, gfp_t flags) +static __always_inline void *____kasan_kmalloc(struct kmem_cache *cache, + const void *object, size_t size, gfp_t flags) {
Also only tail-called.
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unsigned long redzone_start; unsigned long redzone_end;diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h index 2f7400a3412f..d5fe72747a53 100644 --- a/mm/kasan/kasan.h +++ b/mm/kasan/kasan.h@@ -321,7 +321,7 @@ static inline u8 kasan_random_tag(void) { return 0; } #ifdef CONFIG_KASAN_HW_TAGS -static inline void kasan_poison(const void *addr, size_t size, u8 value) +static __always_inline void kasan_poison(const void *addr, size_t size, u8 value) { addr = kasan_reset_tag(addr);@@ -337,7 +337,7 @@ static inline void kasan_poison(const void *addr, size_t size, u8 value) hw_set_mem_tag_range((void *)addr, size, value); } -static inline void kasan_unpoison(const void *addr, size_t size) +static __always_inline void kasan_unpoison(const void *addr, size_t size) {
Not sure about these 2. They should be small, but it's hard to say what is ideal on which architecture.
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u8 tag = get_tag(addr);@@ -354,7 +354,7 @@ static inline void kasan_unpoison(const void *addr, size_t size) hw_set_mem_tag_range((void *)addr, size, tag); } -static inline bool kasan_byte_accessible(const void *addr) +static __always_inline bool kasan_byte_accessible(const void *addr)
This function feels like a macro and if the compiler uninlined it, we could argue it's a bug. But not sure if we need the __always_inline, unless you've seen this uninlined.
{
u8 ptr_tag = get_tag(addr);
u8 mem_tag = hw_get_mem_tag((void *)addr);
--
2.30.0.365.g02bc693789-goog