From: Borislav Petkov (AMD) Date: Sun, 26 Feb 2023 20:04:26 +0000 (+0100) Subject: x86/lib/memmove: Decouple ERMS from FSRM X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=14e4ec9c3e9164c6719f98d8a3065c487be2aaa5;p=linux.git x86/lib/memmove: Decouple ERMS from FSRM Up until now it was perceived that FSRM is an improvement to ERMS and thus it was made dependent on latter. However, there are AMD BIOSes out there which allow for disabling of either features and thus preventing kernels from booting due to the CMP disappearing and thus breaking the logic in the memmove() function. Similar observation happens on some VM migration scenarios. Patch the proper sequences depending on which feature is enabled. Reported-by: Daniel Verkamp Reported-by: Jiri Slaby Signed-off-by: Borislav Petkov (AMD) Link: https://lore.kernel.org/r/Y/yK0dyzI0MMdTie@zn.tnic --- diff --git a/arch/x86/lib/memmove_64.S b/arch/x86/lib/memmove_64.S index 02661861e5dd9..0559b206fb110 100644 --- a/arch/x86/lib/memmove_64.S +++ b/arch/x86/lib/memmove_64.S @@ -38,10 +38,12 @@ SYM_FUNC_START(__memmove) cmp %rdi, %r8 jg 2f - /* FSRM implies ERMS => no length checks, do the copy directly */ +#define CHECK_LEN cmp $0x20, %rdx; jb 1f +#define MEMMOVE_BYTES movq %rdx, %rcx; rep movsb; RET .Lmemmove_begin_forward: - ALTERNATIVE "cmp $0x20, %rdx; jb 1f", "", X86_FEATURE_FSRM - ALTERNATIVE "", "jmp .Lmemmove_erms", X86_FEATURE_ERMS + ALTERNATIVE_2 __stringify(CHECK_LEN), \ + __stringify(CHECK_LEN; MEMMOVE_BYTES), X86_FEATURE_ERMS, \ + __stringify(MEMMOVE_BYTES), X86_FEATURE_FSRM /* * movsq instruction have many startup latency @@ -207,11 +209,6 @@ SYM_FUNC_START(__memmove) movb %r11b, (%rdi) 13: RET - -.Lmemmove_erms: - movq %rdx, %rcx - rep movsb - RET SYM_FUNC_END(__memmove) EXPORT_SYMBOL(__memmove)