Re: [PATCH 6/7] KVM: x86: Ignore benign host accesses to "unsupported" PEBS and BTS MSRs

[Paolo Bonzini]

On 6/13/22 16:09, Sean Christopherson wrote:
> On Sat, Jun 11, 2022, Sean Christopherson wrote:
> > @@ -4122,6 +4132,16 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> >   		msr_info->data = vcpu->arch.guest_fpu.xfd_err;
> >   		break;
> >   #endif
> > +	case MSR_IA32_PEBS_ENABLE:
> > +	case MSR_IA32_DS_AREA:
> > +	case MSR_PEBS_DATA_CFG:
> > +		if (kvm_pmu_is_valid_msr(vcpu, msr_info->index))
> > +			return kvm_pmu_get_msr(vcpu, msr_info);
> > +		/*
> > +		 * Userspace is allowed to read MSRs that KVM reports as
> > +		 * to-be-saved, even if an MSR isn't fully supported.
> > +		 */
> > +		return !msr_info->host_initiated;
>
> Gah, this needs to set msr_info->data.

Might also reuse the F15H case:

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 70364d40e3f7..be39968149e6 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3877,9 +3877,16 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, 
struct msr_data *msr_info)
 	case MSR_DRAM_ENERGY_STATUS:	/* DRAM controller */
 		msr_info->data = 0;
 		break;
+	case MSR_IA32_PEBS_ENABLE:
+	case MSR_IA32_DS_AREA:
+	case MSR_PEBS_DATA_CFG:
 	case MSR_F15H_PERF_CTL0 ... MSR_F15H_PERF_CTR5:
 		if (kvm_pmu_is_valid_msr(vcpu, msr_info->index))
 			return kvm_pmu_get_msr(vcpu, msr_info);
+		/*
+		 * Userspace is allowed to read MSRs that KVM reports as
+		 * to-be-saved, even if an MSR isn't fully supported.
+		 */
 		if (!msr_info->host_initiated)
 			return 1;
 		msr_info->data = 0;


Paolo