Commit e910a53f authored Feb 23, 2022 by Maxim Levitsky Committed by Paolo Bonzini Feb 24, 2022

KVM: x86: nSVM: disallow userspace setting of MSR_AMD64_TSC_RATIO to non...


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

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: 5228eb96 ("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>

parent 6f3c1fc5

arch/x86/kvm/svm/svm.c

+17 −2

Original line number	Diff line number	Diff line
		@@ -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)

		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;