On 2/23/22 12:56, Maxim Levitsky wrote:
If nested tsc scaling is disabled, MSR_AMD64_TSC_RATIO should
never have non default value.
Due to way nested tsc scaling support was implmented in qemu,
it would set this msr to 0 when nested tsc scaling was disabled.
Ignore that value for now, as it causes no harm.
Fixes: 5228eb96a487 ("KVM: x86: nSVM: implement nested TSC scaling")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
---
arch/x86/kvm/svm/svm.c | 19 +++++++++++++++++--
1 file changed, 17 insertions(+), 2 deletions(-)
Queued, thanks.
Paolo
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 7038c76fa841..b80ad471776f 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -2705,8 +2705,23 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
u64 data = msr->data;
switch (ecx) {
case MSR_AMD64_TSC_RATIO:
- if (!msr->host_initiated && !svm->tsc_scaling_enabled)
- return 1;
+
+ if (!svm->tsc_scaling_enabled) {
+
+ if (!msr->host_initiated)
+ return 1;
+ /*
+ * In case TSC scaling is not enabled, always
+ * leave this MSR at the default value.
+ *
+ * Due to bug in qemu 6.2.0, it would try to set
+ * this msr to 0 if tsc scaling is not enabled.
+ * Ignore this value as well.
+ */
+ if (data != 0 && data != svm->tsc_ratio_msr)
+ return 1;
+ break;
+ }
if (data & TSC_RATIO_RSVD)
return 1;
