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x86/cpufeatures: Add support for fast short REP; MOVSB 

>From the Intel Optimization Reference Manual:

3.7.6.1 Fast Short REP MOVSB
Beginning with processors based on Ice Lake Client microarchitecture,
REP MOVSB performance of short operations is enhanced. The enhancement
applies to string lengths between 1 and 128 bytes long.  Support for
fast-short REP MOVSB is enumerated by the CPUID feature flag: CPUID
[EAX=7H, ECX=0H).EDX.FAST_SHORT_REP_MOVSB[bit 4] = 1. There is no change
in the REP STOS performance.

Add an X86_FEATURE_FSRM flag for this.

memmove() avoids REP MOVSB for short (< 32 byte) copies. Check FSRM and
use REP MOVSB for short copies on systems that support it.

 [ bp: Massage and add comment. ]

Signed-off-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20191216214254.26492-1-tony.luck@intel.com
This commit is contained in:
Tony Luck 2019-12-16 13:42:54 -08:00 committed by Borislav Petkov
parent 50cc02e599
commit f444a5ff95
2 changed files with 5 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
arch/x86/include/asm/cpufeatures.h
View File

@ -357,6 +357,7 @@
/* Intel-defined CPU features, CPUID level 0x00000007:0 (EDX), word 18 */
#define X86_FEATURE_AVX512_4VNNIW (18*32+ 2) /* AVX-512 Neural Network Instructions */
#define X86_FEATURE_AVX512_4FMAPS (18*32+ 3) /* AVX-512 Multiply Accumulation Single precision */
#define X86_FEATURE_FSRM (18*32+ 4) /* Fast Short Rep Mov */
#define X86_FEATURE_AVX512_VP2INTERSECT (18*32+ 8) /* AVX-512 Intersect for D/Q */
#define X86_FEATURE_MD_CLEAR (18*32+10) /* VERW clears CPU buffers */
#define X86_FEATURE_TSX_FORCE_ABORT (18*32+13) /* "" TSX_FORCE_ABORT */

7
arch/x86/lib/memmove_64.S
View File

@ -29,10 +29,7 @@
SYM_FUNC_START_ALIAS(memmove)
SYM_FUNC_START(__memmove)
/* Handle more 32 bytes in loop */
mov %rdi, %rax
cmp $0x20, %rdx
jb 1f
/* Decide forward/backward copy mode */
cmp %rdi, %rsi
@ -42,7 +39,9 @@ SYM_FUNC_START(__memmove)
cmp %rdi, %r8
jg 2f
/* FSRM implies ERMS => no length checks, do the copy directly */
.Lmemmove_begin_forward:
ALTERNATIVE "cmp $0x20, %rdx; jb 1f", "", X86_FEATURE_FSRM
ALTERNATIVE "", "movq %rdx, %rcx; rep movsb; retq", X86_FEATURE_ERMS
/*
@ -114,6 +113,8 @@ SYM_FUNC_START(__memmove)
*/
.p2align 4
2:
cmp $0x20, %rdx
jb 1f
cmp $680, %rdx
jb 6f
cmp %dil, %sil