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@vger.kernel.org

Signed-off-by: Maxim Levitsky mlevitsk@redhat.com

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;