arm64/kasan: don't allocate extra shadow memory

arm64/kasan: don't allocate extra shadow memory

We used to read several bytes of the shadow memory in advance.
Therefore additional shadow memory mapped to prevent crash if
speculative load would happen near the end of the mapped shadow memory.

Now we don't have such speculative loads, so we no longer need to map
additional shadow memory.

Link: http://lkml.kernel.org/r/20170601162338.23540-3-aryabinin@virtuozzo.com
Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Acked-by: 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: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>