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x86/copy_user_generic: Optimize copy_user_generic with CPU erms feature

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According to Intel 64 and IA-32 SDM and Optimization Reference Manual, beginning
with Ivybridge, REG string operation using MOVSB and STOSB can provide both
flexible and high-performance REG string operations in cases like memory copy.
Enhancement availability is indicated by CPUID.7.0.EBX[9] (Enhanced REP MOVSB/
STOSB).

If CPU erms feature is detected, patch copy_user_generic with enhanced fast
string version of copy_user_generic.

A few new macros are defined to reduce duplicate code in ALTERNATIVE and
ALTERNATIVE_2.

Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Link: http://lkml.kernel.org/r/1337908785-14015-1-git-send-email-fenghua.yu@intel.com
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
This commit is contained in:
Fenghua Yu 2012-05-24 18:19:45 -07:00 committed by H. Peter Anvin
parent 2f74759056
commit 954e482bde
3 changed files with 70 additions and 16 deletions
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62
arch/x86/include/asm/alternative.h
View File

@ -75,22 +75,53 @@ static inline int alternatives_text_reserved(void *start, void *end)
}
#endif /* CONFIG_SMP */
#define OLDINSTR(oldinstr) "661:\n\t" oldinstr "\n662:\n"
#define b_replacement(number) "663"#number
#define e_replacement(number) "664"#number
#define alt_slen "662b-661b"
#define alt_rlen(number) e_replacement(number)"f-"b_replacement(number)"f"
#define ALTINSTR_ENTRY(feature, number) \
" .long 661b - .\n" /* label */ \
" .long " b_replacement(number)"f - .\n" /* new instruction */ \
" .word " __stringify(feature) "\n" /* feature bit */ \
" .byte " alt_slen "\n" /* source len */ \
" .byte " alt_rlen(number) "\n" /* replacement len */
#define DISCARD_ENTRY(number) /* rlen <= slen */ \
" .byte 0xff + (" alt_rlen(number) ") - (" alt_slen ")\n"
#define ALTINSTR_REPLACEMENT(newinstr, feature, number) /* replacement */ \
b_replacement(number)":\n\t" newinstr "\n" e_replacement(number) ":\n\t"
/* alternative assembly primitive: */
#define ALTERNATIVE(oldinstr, newinstr, feature) \
\
"661:\n\t" oldinstr "\n662:\n" \
OLDINSTR(oldinstr) \
".section .altinstructions,\"a\"\n" \
" .long 661b - .\n" /* label */ \
" .long 663f - .\n" /* new instruction */ \
" .word " __stringify(feature) "\n" /* feature bit */ \
" .byte 662b-661b\n" /* sourcelen */ \
" .byte 664f-663f\n" /* replacementlen */ \
ALTINSTR_ENTRY(feature, 1) \
".previous\n" \
".section .discard,\"aw\",@progbits\n" \
" .byte 0xff + (664f-663f) - (662b-661b)\n" /* rlen <= slen */ \
DISCARD_ENTRY(1) \
".previous\n" \
".section .altinstr_replacement, \"ax\"\n" \
"663:\n\t" newinstr "\n664:\n" /* replacement */ \
ALTINSTR_REPLACEMENT(newinstr, feature, 1) \
".previous"
#define ALTERNATIVE_2(oldinstr, newinstr1, feature1, newinstr2, feature2)\
OLDINSTR(oldinstr) \
".section .altinstructions,\"a\"\n" \
ALTINSTR_ENTRY(feature1, 1) \
ALTINSTR_ENTRY(feature2, 2) \
".previous\n" \
".section .discard,\"aw\",@progbits\n" \
DISCARD_ENTRY(1) \
DISCARD_ENTRY(2) \
".previous\n" \
".section .altinstr_replacement, \"ax\"\n" \
ALTINSTR_REPLACEMENT(newinstr1, feature1, 1) \
ALTINSTR_REPLACEMENT(newinstr2, feature2, 2) \
".previous"
/*
@ -139,6 +170,19 @@ static inline int alternatives_text_reserved(void *start, void *end)
asm volatile (ALTERNATIVE("call %P[old]", "call %P[new]", feature) \
: output : [old] "i" (oldfunc), [new] "i" (newfunc), ## input)
/*
* Like alternative_call, but there are two features and respective functions.
* If CPU has feature2, function2 is used.
* Otherwise, if CPU has feature1, function1 is used.
* Otherwise, old function is used.
*/
#define alternative_call_2(oldfunc, newfunc1, feature1, newfunc2, feature2, \
output, input...) \
asm volatile (ALTERNATIVE_2("call %P[old]", "call %P[new1]", feature1,\
"call %P[new2]", feature2) \
: output : [old] "i" (oldfunc), [new1] "i" (newfunc1), \
[new2] "i" (newfunc2), ## input)
/*
* use this macro(s) if you need more than one output parameter
* in alternative_io

11
arch/x86/include/asm/uaccess_64.h
View File

@ -17,6 +17,8 @@
/* Handles exceptions in both to and from, but doesn't do access_ok */
__must_check unsigned long
copy_user_enhanced_fast_string(void *to, const void *from, unsigned len);
__must_check unsigned long
copy_user_generic_string(void *to, const void *from, unsigned len);
__must_check unsigned long
copy_user_generic_unrolled(void *to, const void *from, unsigned len);
@ -26,9 +28,16 @@ copy_user_generic(void *to, const void *from, unsigned len)
{
unsigned ret;
alternative_call(copy_user_generic_unrolled,
/*
* If CPU has ERMS feature, use copy_user_enhanced_fast_string.
* Otherwise, if CPU has rep_good feature, use copy_user_generic_string.
* Otherwise, use copy_user_generic_unrolled.
*/
alternative_call_2(copy_user_generic_unrolled,
copy_user_generic_string,
X86_FEATURE_REP_GOOD,
copy_user_enhanced_fast_string,
X86_FEATURE_ERMS,
ASM_OUTPUT2("=a" (ret), "=D" (to), "=S" (from),
"=d" (len)),
"1" (to), "2" (from), "3" (len)

1
arch/x86/kernel/x8664_ksyms_64.c
View File

@ -28,6 +28,7 @@ EXPORT_SYMBOL(__put_user_8);
EXPORT_SYMBOL(copy_user_generic_string);
EXPORT_SYMBOL(copy_user_generic_unrolled);
EXPORT_SYMBOL(copy_user_enhanced_fast_string);
EXPORT_SYMBOL(__copy_user_nocache);
EXPORT_SYMBOL(_copy_from_user);
EXPORT_SYMBOL(_copy_to_user);