Messages in this thread Patch in this message | | | Date | Mon, 19 Oct 2015 12:16:12 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH] x86: Add an explicit barrier() to clflushopt() |
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On Mon, Oct 19, 2015 at 10:58:55AM +0100, Chris Wilson wrote: > During testing we observed that the last cacheline was not being flushed > from a > > mb() > for (addr = addr & -clflush_size; addr < end; addr += clflush_size) > clflushopt(); > mb() > > loop (where the initial addr and end were not cacheline aligned). > > Changing the loop from addr < end to addr <= end, or replacing the > clflushopt() with clflush() both fixed the testcase. Hinting that GCC > was miscompling the assembly within the loop and specifically the > alternative within clflushopt() was confusing the loop optimizer. > > Adding a barrier() into clflushopt() is enough for GCC to dtrt, but > solving why GCC is not seeing the constraints from the alternative_io() > would be smarter...
Hmm, would something like adding the memory clobber to the alternative_io() definition work?
--- diff --git a/arch/x86/include/asm/alternative.h b/arch/x86/include/asm/alternative.h index 7bfc85bbb8ff..d923e5dacdb1 100644 --- a/arch/x86/include/asm/alternative.h +++ b/arch/x86/include/asm/alternative.h @@ -207,7 +207,7 @@ static inline int alternatives_text_reserved(void *start, void *end) /* Like alternative_input, but with a single output argument */ #define alternative_io(oldinstr, newinstr, feature, output, input...) \ asm volatile (ALTERNATIVE(oldinstr, newinstr, feature) \ - : output : "i" (0), ## input) + : output : "i" (0), ## input : "memory") /* Like alternative_io, but for replacing a direct call with another one. */ #define alternative_call(oldfunc, newfunc, feature, output, input...) \ -- Regards/Gruss, Boris.
ECO tip #101: Trim your mails when you reply.
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