[PATCH 2/2] x86/bugs: Fix the AMD SSBD usage of the SPEC_CTRL MSR

[Tom Lendacky]

On AMD, the presence of the MSR_SPEC_CTRL feature does not imply that the
SSBD mitigation support should use the SPEC_CTRL MSR. Other features could
have caused the MSR_SPEC_CTRL feature to be set, while a different SSBD
mitigation option is in place.

Update the SSBD support to check for the actual SSBD features that will
use the SPEC_CTRL MSR.

Fixes: 6ac2f49edb1e ("x86/bugs: Add AMD's SPEC_CTRL MSR usage")
Signed-off-by: Tom Lendacky <thomas.lenda...@amd.com>
---
 arch/x86/kernel/cpu/bugs.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 404df26..5c0ea39 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -155,7 +155,8 @@ enum spectre_v2_mitigation_cmd {
                guestval |= guest_spec_ctrl & x86_spec_ctrl_mask;
 
                /* SSBD controlled in MSR_SPEC_CTRL */
-               if (static_cpu_has(X86_FEATURE_SPEC_CTRL_SSBD))
+               if (static_cpu_has(X86_FEATURE_SPEC_CTRL_SSBD) ||
+                   static_cpu_has(X86_FEATURE_AMD_SSBD))
                        hostval |= ssbd_tif_to_spec_ctrl(ti->flags);
 
                if (hostval != guestval) {
@@ -533,9 +534,10 @@ static enum ssb_mitigation __init 
__ssb_select_mitigation(void)
                 * Intel uses the SPEC CTRL MSR Bit(2) for this, while AMD may
                 * use a completely different MSR and bit dependent on family.
                 */
-               if (!static_cpu_has(X86_FEATURE_MSR_SPEC_CTRL))
+               if (!static_cpu_has(X86_FEATURE_SPEC_CTRL_SSBD) &&
+                   !static_cpu_has(X86_FEATURE_AMD_SSBD)) {
                        x86_amd_ssb_disable();
-               else {
+               } else {
                        x86_spec_ctrl_base |= SPEC_CTRL_SSBD;
                        x86_spec_ctrl_mask |= SPEC_CTRL_SSBD;
                        wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);