RE: [PATCH v5 1/5] x86/asm: Carve out a generic movdir64b() helper for general usage
From: David Laight <hidden>
Date: 2020-09-24 08:24:53
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- 2020-09-24 · Re: [PATCH v5 1/5] x86/asm: Carve out a generic movdir64b() helper for general usage · Dave Jiang <dave.jiang@intel.com>
- 2020-09-24 · RE: [PATCH v5 1/5] x86/asm: Carve out a generic movdir64b() helper for general usage · David Laight <hidden>
- 2020-09-24 · Re: [PATCH v5 1/5] x86/asm: Carve out a generic movdir64b() helper for general usage · Borislav Petkov <bp@alien8.de>
From: Dave Jiang
quoted hunk
Sent: 24 September 2020 00:11 The MOVDIR64B instruction can be used by other wrapper instructions. Move the asm code to special_insns.h and have iosubmit_cmds512() call the asm function. Signed-off-by: Dave Jiang <dave.jiang@intel.com> Reviewed-by: Tony Luck <tony.luck@intel.com> --- arch/x86/include/asm/io.h | 17 +++-------------- arch/x86/include/asm/special_insns.h | 19 +++++++++++++++++++ 2 files changed, 22 insertions(+), 14 deletions(-)diff --git a/arch/x86/include/asm/io.h b/arch/x86/include/asm/io.h index e1aa17a468a8..d726459d08e5 100644 --- a/arch/x86/include/asm/io.h +++ b/arch/x86/include/asm/io.h
...
quoted hunk
diff --git a/arch/x86/include/asm/special_insns.h b/arch/x86/include/asm/special_insns.h index 59a3e13204c3..2a5abd27bb86 100644 --- a/arch/x86/include/asm/special_insns.h +++ b/arch/x86/include/asm/special_insns.h@@ -234,6 +234,25 @@ static inline void clwb(volatile void *__p) #define nop() asm volatile ("nop") +/* The dst parameter must be 64-bytes aligned */ +static inline void movdir64b(void *dst, const void *src) +{ + /* + * Note that this isn't an "on-stack copy", just definition of "dst" + * as a pointer to 64-bytes of stuff that is going to be overwritten. + * In the MOVDIR64B case that may be needed as you can use the + * MOVDIR64B instruction to copy arbitrary memory around. This trick + * lets the compiler know how much gets clobbered. + */ + volatile struct { char _[64]; } *__dst = dst; + + /* MOVDIR64B [rdx], rax */ + asm volatile(".byte 0x66, 0x0f, 0x38, 0xf8, 0x02" + : + : "m" (*(struct { char _[64];} **)src), "a" (__dst) + : "memory"); +} + #endif /* __KERNEL__ */
You've lost the "d" (src).
You don't need the 'memory' clobber, just:
static inline void movdir64b(void *dst, const void *src)
{
/*
* 64 bytes from dst are marked as modified for completeness.
* Since the writes bypass the cache later reads may return
* old data anyway.
*/
/* MOVDIR64B [rdx], rax */
asm volatile (".byte 0x66, 0x0f, 0x38, 0xf8, 0x02"
: "=m" ((struct { char _[64];} *)dst),
: "m" ((struct { char _[64];} *)src), "d" (src), "a" (dst));
}
I've checked that the "m" constraint on src does force (at least one
version of) gcc to actually write to the supplied buffer.
David
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