diff options
| author | Linus Torvalds <torvalds@linux-foundation.org> | 2023-04-15 23:14:59 +0300 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2023-04-19 03:05:28 +0300 |
| commit | adfcf4231b8cbc2d9c1e7bfaa965b907e60639eb (patch) | |
| tree | 4aceffad12112ff5fab00b48005fab8c55cc8404 /arch/x86/lib | |
| parent | 20f3337d350c4e1b4ac66d731fd4e98565bf6cc0 (diff) | |
| download | linux-adfcf4231b8cbc2d9c1e7bfaa965b907e60639eb.tar.xz | |
x86: don't use REP_GOOD or ERMS for user memory copies
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>
Diffstat (limited to 'arch/x86/lib')
| -rw-r--r-- | arch/x86/lib/copy_user_64.S | 51 |
1 files changed, 7 insertions, 44 deletions
diff --git a/arch/x86/lib/copy_user_64.S b/arch/x86/lib/copy_user_64.S index 9dec1b38a98f..d0283bc7567d 100644 --- a/arch/x86/lib/copy_user_64.S +++ b/arch/x86/lib/copy_user_64.S @@ -104,8 +104,8 @@ SYM_FUNC_START(copy_user_generic_unrolled) SYM_FUNC_END(copy_user_generic_unrolled) EXPORT_SYMBOL(copy_user_generic_unrolled) -/* Some CPUs run faster using the string copy instructions. - * This is also a lot simpler. Use them when possible. +/* + * Some CPUs support FSRM for Fast Short REP MOVS. * * Only 4GB of copy is supported. This shouldn't be a problem * because the kernel normally only writes from/to page sized chunks @@ -122,58 +122,21 @@ EXPORT_SYMBOL(copy_user_generic_unrolled) * Output: * eax uncopied bytes or 0 if successful. */ -SYM_FUNC_START(copy_user_generic_string) +SYM_FUNC_START(copy_user_fast_string) ASM_STAC - cmpl $8,%edx - jb 2f /* less than 8 bytes, go to byte copy loop */ - ALIGN_DESTINATION movl %edx,%ecx - shrl $3,%ecx - andl $7,%edx -1: rep movsq -2: movl %edx,%ecx -3: rep movsb +1: rep movsb xorl %eax,%eax ASM_CLAC RET -11: leal (%rdx,%rcx,8),%ecx -12: movl %ecx,%edx /* ecx is zerorest also */ - jmp .Lcopy_user_handle_tail - - _ASM_EXTABLE_CPY(1b, 11b) - _ASM_EXTABLE_CPY(3b, 12b) -SYM_FUNC_END(copy_user_generic_string) -EXPORT_SYMBOL(copy_user_generic_string) - -/* - * Some CPUs are adding enhanced REP MOVSB/STOSB instructions. - * It's recommended to use enhanced REP MOVSB/STOSB if it's enabled. - * - * Input: - * rdi destination - * rsi source - * rdx count - * - * Output: - * eax uncopied bytes or 0 if successful. - */ -SYM_FUNC_START(copy_user_enhanced_fast_string) - ASM_STAC - /* CPUs without FSRM should avoid rep movsb for short copies */ - ALTERNATIVE "cmpl $64, %edx; jb copy_user_short_string", "", X86_FEATURE_FSRM - movl %edx,%ecx -1: rep movsb - xorl %eax,%eax +12: movl %ecx,%eax /* ecx is zerorest also */ ASM_CLAC RET -12: movl %ecx,%edx /* ecx is zerorest also */ - jmp .Lcopy_user_handle_tail - _ASM_EXTABLE_CPY(1b, 12b) -SYM_FUNC_END(copy_user_enhanced_fast_string) -EXPORT_SYMBOL(copy_user_enhanced_fast_string) +SYM_FUNC_END(copy_user_fast_string) +EXPORT_SYMBOL(copy_user_fast_string) /* * Try to copy last bytes and clear the rest if needed. |