Disallow writes to MSR_IA32_TSC for Secure TSC enabled SNP guests. Even if
KVM attempts to emulate such writes, TSC calculation will ignore the
TSC_SCALE and TSC_OFFSET present in the VMCB. Instead, it will use
GUEST_TSC_SCALE and GUEST_TSC_OFFSET stored in the VMSA.
Additionally, incorporate a check for protected guest state to allow the
VMM to initialize the TSC MSR.
Signed-off-by: Nikunj A Dadhania <nikunj@xxxxxxx>
---
arch/x86/kvm/svm/svm.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 93cf508f983c..7463466f5126 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3161,6 +3161,20 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
svm->tsc_aux = data;
break;
+ case MSR_IA32_TSC:
+ /*
+ * If Secure TSC is enabled, do not emulate TSC write as TSC calculation
+ * ignores the TSC_OFFSET and TSC_SCALE control fields, record the error
+ * and return a #GP. Allow the TSC to be initialized until the guest state
+ * is protected to prevent unexpected VMM errors.
+ */
+ if (vcpu->arch.guest_state_protected && snp_secure_tsc_enabled(vcpu->kvm)) {
+ vcpu_unimpl(vcpu, "unimplemented IA32_TSC for secure tsc\n");
+ return 1;
+ }
+
+ ret = kvm_set_msr_common(vcpu, msr);
+ break;
case MSR_IA32_DEBUGCTLMSR:
if (!lbrv) {
kvm_pr_unimpl_wrmsr(vcpu, ecx, data);
--
2.43.0
