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KVM: x86: nSVM: disallow userspace setting of MSR_AMD64_TSC_RATIO to non default value when tsc scaling disabled

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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: 5228eb96a4 ("KVM: x86: nSVM: implement nested TSC scaling")
Cc: stable@vger.kernel.org

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20220223115649.319134-1-mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Maxim Levitsky 2022-02-23 13:56:49 +02:00 committed by Paolo Bonzini
parent 6f3c1fc53d
commit e910a53fb4
1 changed files with 17 additions and 2 deletions
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19
arch/x86/kvm/svm/svm.c
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@ -2693,8 +2693,23 @@ 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;