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

Paolo Bonzini
2022-06-20T15:02:09Z

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