[PATCH] x86/speculation/srbds: do not try to turn mitigation off when not supported

[Thadeu Lima de Souza Cascardo]

When SRBDS is mitigated by TSX OFF, update_srbds_msr will still read and
write to MSR_IA32_MCU_OPT_CTRL even when that is not supported by the
microcode.

Checking for X86_FEATURE_SRBDS_CTRL as a CPU feature available makes more
sense than checking for SRBDS_MITIGATION_UCODE_NEEDED as the found
"mitigation".

Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@xxxxxxxxxxxxx>
Acked-by: John Johansen <john.johansen@xxxxxxxxxxxxx>
Acked-by: Steve Beattie <sbeattie@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
---
 arch/x86/kernel/cpu/bugs.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index b6f887be440c..ee5bdca7fd30 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -432,7 +432,7 @@ void update_srbds_msr(void)
 	if (boot_cpu_has(X86_FEATURE_HYPERVISOR))
 		return;
 
-	if (srbds_mitigation == SRBDS_MITIGATION_UCODE_NEEDED)
+	if (!boot_cpu_has(X86_FEATURE_SRBDS_CTRL))
 		return;
 
 	rdmsrl(MSR_IA32_MCU_OPT_CTRL, mcu_ctrl);
-- 
2.25.1