x86/bugs: Fix the AMD SSBD usage of the SPEC_CTRL MSR

commit 612bc3b3 upstream.

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.
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Borislav Petkov <bpetkov@suse.de>
Cc: David Woodhouse <dwmw@amazon.co.uk>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 6ac2f49e ("x86/bugs: Add AMD's SPEC_CTRL MSR usage")
Link: http://lkml.kernel.org/r/20180702213602.29202.33151.stgit@tlendack-t1.amdoffice.netSigned-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/x86/kernel/cpu/bugs.c

@@ -165,7 +165,8 @@ x86_virt_spec_ctrl(u64 guest_spec_ctrl, u64 guest_virt_spec_ctrl, bool setguest)
 		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) {
@@ -534,9 +535,10 @@ 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);