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x86/lib/memmove: Decouple ERMS from FSRM

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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 <dverkamp@chromium.org>
Reported-by: Jiri Slaby <jirislaby@kernel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/Y/yK0dyzI0MMdTie@zn.tnic
This commit is contained in:
Borislav Petkov (AMD)
2023-02-26 21:04:26 +01:00
parent 270a69c448
commit 14e4ec9c3e
1 changed files with 5 additions and 8 deletions
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13
arch/x86/lib/memmove_64.S
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@@ -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)