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x86, mem: clear_page_64.S: Support clear_page() with enhanced REP MOV…

…SB/STOSB

Intel processors are adding enhancements to REP MOVSB/STOSB and the use of
REP MOVSB/STOSB for optimal memcpy/memset or similar functions is recommended.
Enhancement availability is indicated by CPUID.7.0.EBX[9] (Enhanced REP MOVSB/
STOSB).

Support clear_page() with rep stosb for processor supporting enhanced REP MOVSB
/STOSB. On processors supporting enhanced REP MOVSB/STOSB, the alternative
clear_page_c_e function using enhanced REP STOSB overrides the original function
and the fast string function.

Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Link: http://lkml.kernel.org/r/1305671358-14478-6-git-send-email-fenghua.yu@intel.com
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
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Fenghua Yu H. Peter Anvin
Fenghua Yu authored and H. Peter Anvin committed May 17, 2011
1 parent 9072d11 commit e365c9df2f2f001450decf9512412d2d5bd1cdef
Showing with 24 additions and 9 deletions.
  1. +24 −9 arch/x86/lib/clear_page_64.S
@@ -1,5 +1,6 @@
#include <linux/linkage.h>
#include <asm/dwarf2.h>
#include <asm/alternative-asm.h>
/*
* Zero a page.
@@ -14,6 +15,15 @@ ENTRY(clear_page_c)
CFI_ENDPROC
ENDPROC(clear_page_c)
ENTRY(clear_page_c_e)
CFI_STARTPROC
movl $4096,%ecx
xorl %eax,%eax
rep stosb
ret
CFI_ENDPROC
ENDPROC(clear_page_c_e)
ENTRY(clear_page)
CFI_STARTPROC
xorl %eax,%eax
@@ -38,21 +48,26 @@ ENTRY(clear_page)
.Lclear_page_end:
ENDPROC(clear_page)
/* Some CPUs run faster using the string instructions.
It is also a lot simpler. Use this when possible */
/*
* Some CPUs support enhanced REP MOVSB/STOSB instructions.
* It is recommended to use this when possible.
* If enhanced REP MOVSB/STOSB is not available, try to use fast string.
* Otherwise, use original function.
*
*/
#include <asm/cpufeature.h>
.section .altinstr_replacement,"ax"
1: .byte 0xeb /* jmp <disp8> */
.byte (clear_page_c - clear_page) - (2f - 1b) /* offset */
2:
2: .byte 0xeb /* jmp <disp8> */
.byte (clear_page_c_e - clear_page) - (3f - 2b) /* offset */
3:
.previous
.section .altinstructions,"a"
.align 8
.quad clear_page
.quad 1b
.word X86_FEATURE_REP_GOOD
.byte .Lclear_page_end - clear_page
.byte 2b - 1b
altinstruction_entry clear_page,1b,X86_FEATURE_REP_GOOD,\
.Lclear_page_end-clear_page, 2b-1b
altinstruction_entry clear_page,2b,X86_FEATURE_ERMS, \
.Lclear_page_end-clear_page,3b-2b
.previous

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