mm/kasan: get rid of speculative shadow checks
authorAndrey Ryabinin <aryabinin@virtuozzo.com>
Mon, 10 Jul 2017 22:50:24 +0000 (15:50 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Mon, 10 Jul 2017 23:32:33 +0000 (16:32 -0700)
commitc634d807d98e3e7def43e72d28528c84c612ab98
treef716e5888283eda8dcfa084b28c4badd29bdfe09
parent458f7920f9b1e6c313944d498c440f8599b8a136
mm/kasan: get rid of speculative shadow checks

For some unaligned memory accesses we have to check additional byte of
the shadow memory.  Currently we load that byte speculatively to have
only single load + branch on the optimistic fast path.

However, this approach has some downsides:

 - It's unaligned access, so this prevents porting KASAN on
   architectures which doesn't support unaligned accesses.

 - We have to map additional shadow page to prevent crash if speculative
   load happens near the end of the mapped memory. This would
   significantly complicate upcoming memory hotplug support.

I wasn't able to notice any performance degradation with this patch.  So
these speculative loads is just a pain with no gain, let's remove them.

Link: http://lkml.kernel.org/r/20170601162338.23540-1-aryabinin@virtuozzo.com
Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Acked-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm/kasan/kasan.c