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x86: don't use REP_GOOD or ERMS for user memory copies

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The modern target to use is FSRM (Fast Short REP MOVS), and the other
cases should only be used for bigger areas (ie mainly things like page
clearing).

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Linus Torvalds
2023-04-15 13:14:59 -07:00
parent 20f3337d35
commit adfcf4231b
2 changed files with 13 additions and 55 deletions
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15
arch/x86/include/asm/uaccess_64.h
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@@ -18,9 +18,7 @@
/* 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);
copy_user_fast_string(void *to, const void *from, unsigned len);
__must_check unsigned long
copy_user_generic_unrolled(void *to, const void *from, unsigned len);
@@ -30,15 +28,12 @@ copy_user_generic(void *to, const void *from, unsigned len)
unsigned ret;
/*
* If CPU has ERMS feature, use copy_user_enhanced_fast_string.
* Otherwise, if CPU has rep_good feature, use copy_user_generic_string.
* If CPU has FSRM feature, use 'rep movs'.
* 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,
alternative_call(copy_user_generic_unrolled,
copy_user_fast_string,
X86_FEATURE_FSRM,
ASM_OUTPUT2("=a" (ret), "=D" (to), "=S" (from),
"=d" (len)),
"1" (to), "2" (from), "3" (len)