[tip: x86/urgent] x86/bugs: Use SBPB in write_ibpb() if applicable

[tip-bot2 for Josh Poimboeuf]

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     fc9fd3f98423367c79e0bd85a9515df26dc1b3cc
Gitweb:        https://git.kernel.org/tip/fc9fd3f98423367c79e0bd85a9515df26dc1b3cc
Author:        Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
AuthorDate:    Tue, 08 Apr 2025 14:47:31 -07:00
Committer:     Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Wed, 09 Apr 2025 12:41:30 +02:00

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@xxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Link: https://lore.kernel.org/r/17c5dcd14b29199b75199d67ff7758de9d9a4928.1744148254.git.jpoimboe@xxxxxxxxxx
---
 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 cabe65a..175958b 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