Re: [PATCH] KVM: VMX: Always treat MSR_IA32_PERF_CAPABILITIES as a valid PMU MSR

["Xu, Like" <like.xu@intel.com>]

On 2020/6/4 4:33, Sean Christopherson wrote:
> Unconditionally return true when querying the validity of
> MSR_IA32_PERF_CAPABILITIES so as to defer the validity check to
> intel_pmu_{get,set}_msr(), which can properly give the MSR a pass when
> the access is initiated from host userspace.
Regardless of  the MSR is emulated or not, is it a really good assumption that
the guest cpuids are not properly ready when we do initialization from host 
userspace
?
> The MSR is emulated so
> there is no underlying hardware dependency to worry about.
>
> Fixes: 27461da31089a ("KVM: x86/pmu: Support full width counting")
> Cc: Like Xu <like.xu@linux.intel.com>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> ---
>
> KVM selftests are completely hosed for me, everything fails on KVM_GET_MSRS.
At least I tried "make --silent -C tools/testing/selftests/kvm run_tests"
and how do I reproduce the "everything fails" for this issue ?

Thanks,
Like Xu
>
>   arch/x86/kvm/vmx/pmu_intel.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
> index d33d890b605f..bdcce65c7a1d 100644
> --- a/arch/x86/kvm/vmx/pmu_intel.c
> +++ b/arch/x86/kvm/vmx/pmu_intel.c
> @@ -181,7 +181,7 @@ static bool intel_is_valid_msr(struct kvm_vcpu *vcpu, u32 msr)
>   		ret = pmu->version > 1;
>   		break;
>   	case MSR_IA32_PERF_CAPABILITIES:
> -		ret = guest_cpuid_has(vcpu, X86_FEATURE_PDCM);
> +		ret = 1;
>   		break;
>   	default:
>   		ret = get_gp_pmc(pmu, msr, MSR_IA32_PERFCTR0) ||