linux-kernel - [PATCH v4 2/6] x86/bugs: Use SBPB in write

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Message-ID: <17c5dcd14b29199b75199d67ff7758de9d9a4928.1744148254.git.jpoimboe@kernel.org>
Date: Tue,  8 Apr 2025 14:47:31 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: x86@...nel.org
Cc: linux-kernel@...r.kernel.org,
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Subject: [PATCH v4 2/6] x86/bugs: Use SBPB in write_ibpb() if applicable

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@...nel.org>
---
 arch/x86/entry/entry.S | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/entry/entry.S b/arch/x86/entry/entry.S
index cabe65ac8379..175958b02f2b 100644
--- a/arch/x86/entry/entry.S
+++ b/arch/x86/entry/entry.S
@@ -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
 
-- 
2.49.0