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Subject: Re: [PATCH][v6] KVM: X86: support APERF/MPERF registers
To:     Jim Mattson <jmattson@google.com>
Cc:     Xiaoyao Li <xiaoyao.li@intel.com>,
        Li RongQing <lirongqing@baidu.com>,
        LKML <linux-kernel@vger.kernel.org>,
        kvm list <kvm@vger.kernel.org>,
        the arch/x86 maintainers <x86@kernel.org>,
        "H . Peter Anvin" <hpa@zytor.com>, Borislav Petkov <bp@alien8.de>,
        Ingo Molnar <mingo@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Wanpeng Li <wanpengli@tencent.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        wei.huang2@amd.com
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 <b70d03dd-947f-dee5-5499-3b381372497d@intel.com>
 <72a75924-c3cb-6b23-62bd-67b739dec166@redhat.com>
 <CALMp9eSrDehftA5o6tU2sE_098F2ucztYtzhvgguYDnWqwHJaw@mail.gmail.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <a1aa9cc5-96c7-11fe-17e1-22fe46b940f3@redhat.com>
Date:   Fri, 5 Jun 2020 19:22:01 +0200
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On 05/06/20 19:16, Jim Mattson wrote:
>>>> @@ -4930,6 +4939,11 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
>>>>           kvm->arch.exception_payload_enabled = cap->args[0];
>>>>           r = 0;
>>>>           break;
>>>> +    case KVM_CAP_APERFMPERF:
>>>> +        kvm->arch.aperfmperf_mode =
>>>> +            boot_cpu_has(X86_FEATURE_APERFMPERF) ? cap->args[0] : 0;
>>> Shouldn't check whether cap->args[0] is a valid value?
>> Yes, only valid values should be allowed.
>>
>> Also, it should fail with -EINVAL if the host does not have
>> X86_FEATURE_APERFMPERF.
> Should enabling/disabling this capability be disallowed once vCPUs
> have been created?
> 

That's a good idea, yes.

Paolo