linux-kernel - Re: [PATCH v2] KVM: SVM: emulate MSR_IA32_PERF

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Message-ID: <8e3b2eef-b4f1-01cc-e033-c1ece70bd7db@redhat.com>
Date:   Thu, 18 Jun 2020 15:21:54 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>, kvm@...r.kernel.org
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Like Xu <like.xu@...ux.intel.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] KVM: SVM: emulate MSR_IA32_PERF_CAPABILITIES

On 18/06/20 14:54, Vitaly Kuznetsov wrote:
> Paolo Bonzini <pbonzini@...hat.com> writes:
> 
>> On 18/06/20 13:13, Vitaly Kuznetsov wrote:
>>> state_test/smm_test selftests are failing on AMD with:
>>> "Unexpected result from KVM_GET_MSRS, r: 51 (failed MSR was 0x345)"
>>>
>>> MSR_IA32_PERF_CAPABILITIES is an emulated MSR on Intel but it is not
>>> known to AMD code, emulate it there too (by returning 0 and allowing
>>> userspace to write 0). This way the code is better prepared to the
>>> eventual appearance of the feature in AMD hardware.
>>>
>>> Fixes: 27461da31089 ("KVM: x86/pmu: Support full width counting")
>>> Suggested-by: Jim Mattson <jmattson@...gle.com>
>>> Suggested-by: Paolo Bonzini <pbonzini@...hat.com>
>>> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
>>> ---
>>>  arch/x86/kvm/svm/pmu.c | 29 ++++++++++++++++++++++++++++-
>>>  1 file changed, 28 insertions(+), 1 deletion(-)
>> This is okay and I'll apply it, but it would be even better to move the
>> whole handling of the MSR to common x86 code.
> I thought about that but intel_pmu_set_msr() looks at
> vmx_get_perf_capabilities(), we'll need to abstract this somehow.

Indeed, you could use kvm_get_msr_feature for that.

Paolo