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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>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.