linux-kernel - Re: [PATCH][v6] KVM: X86: support APERF/MPERF registers

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Date:   Fri, 5 Jun 2020 19:22:01 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Jim Mattson <jmattson@...gle.com>
Cc:     Xiaoyao Li <xiaoyao.li@...el.com>,
        Li RongQing <lirongqing@...du.com>,
        LKML <linux-kernel@...r.kernel.org>,
        kvm list <kvm@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Wanpeng Li <wanpengli@...cent.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        wei.huang2@....com
Subject: Re: [PATCH][v6] KVM: X86: support APERF/MPERF registers

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