KVM: x86: expose MSR_TSC_AUX to userspace

commit 9dbe6cf9 upstream.

If we do not do this, it is not properly saved and restored across
migration.  Windows notices due to its self-protection mechanisms,
and is very upset about it (blue screen of death).

Cc: Radim Krcmar <rkrcmar@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
[bwh: Backported to 3.2:
 - We didn't yet have the switch() in kvm_init_msr_list as MPX is not
   supported at all
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

arch/x86/kvm/x86.c

@@ -834,7 +834,8 @@ static u32 msrs_to_save[] = {
 #ifdef CONFIG_X86_64
 	MSR_CSTAR, MSR_KERNEL_GS_BASE, MSR_SYSCALL_MASK, MSR_LSTAR,
 #endif
-	MSR_IA32_TSC, MSR_IA32_CR_PAT, MSR_VM_HSAVE_PA
+	MSR_IA32_TSC, MSR_IA32_CR_PAT, MSR_VM_HSAVE_PA,
+	MSR_TSC_AUX,
 };
 
 static unsigned num_msrs_to_save;
@@ -3867,6 +3868,20 @@ static void kvm_init_msr_list(void)
 	for (i = j = KVM_SAVE_MSRS_BEGIN; i < ARRAY_SIZE(msrs_to_save); i++) {
 		if (rdmsr_safe(msrs_to_save[i], &dummy[0], &dummy[1]) < 0)
 			continue;
+
+		/*
+		 * Even MSRs that are valid in the host may not be exposed
+		 * to the guests in some cases.
+		 */
+		switch (msrs_to_save[i]) {
+		case MSR_TSC_AUX:
+			if (!kvm_x86_ops->rdtscp_supported())
+				continue;
+			break;
+		default:
+			break;
+		}
+
 		if (j < i)
 			msrs_to_save[j] = msrs_to_save[i];
 		j++;