linux-kernel - Re: [PATCH] KVM: VMX: Always treat MSR_IA32_PERF

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Date:   Thu, 4 Jun 2020 09:37:59 +0800
From:   "Xu, Like" <like.xu@...el.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Like Xu <like.xu@...ux.intel.com>
Subject: Re: [PATCH] KVM: VMX: Always treat MSR_IA32_PERF_CAPABILITIES as a
 valid PMU MSR

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@...ux.intel.com>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.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) ||