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x86/bugs: Use SBPB in write_ibpb() if applicable

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write_ibpb() does IBPB, which (among other things) flushes branch type
predictions on AMD.  If the CPU has SRSO_NO, or if the SRSO mitigation
has been disabled, branch type flushing isn't needed, in which case the
lighter-weight SBPB can be used.

The 'x86_pred_cmd' variable already keeps track of whether IBPB or SBPB
should be used.  Use that instead of hardcoding IBPB.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/17c5dcd14b29199b75199d67ff7758de9d9a4928.1744148254.git.jpoimboe@kernel.org
This commit is contained in:
Josh Poimboeuf
2025-04-08 14:47:31 -07:00
committed by Ingo Molnar
parent 13235d6d50
commit fc9fd3f984
1 changed files with 1 additions and 1 deletions
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2
arch/x86/entry/entry.S
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@@ -21,7 +21,7 @@
SYM_FUNC_START(write_ibpb)
ANNOTATE_NOENDBR
movl $MSR_IA32_PRED_CMD, %ecx
movl $PRED_CMD_IBPB, %eax
movl _ASM_RIP(x86_pred_cmd), %eax
xorl %edx, %edx
wrmsr