linux-kernel - Re: [PATCH][v2] kvm: x86: emulate APERF/MPERF registers

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Message-ID: <5aa01c91-b874-fd4f-a1fb-1d008753ca84@intel.com>
Date:   Thu, 30 Apr 2020 14:49:24 +0800
From:   Xiaoyao Li <xiaoyao.li@...el.com>
To:     Li RongQing <lirongqing@...du.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, x86@...nel.org, hpa@...or.com, bp@...en8.de,
        mingo@...hat.com, tglx@...utronix.de, joro@...tes.org,
        jmattson@...gle.com, wanpengli@...cent.com, vkuznets@...hat.com,
        sean.j.christopherson@...el.com, pbonzini@...hat.com
Subject: Re: [PATCH][v2] kvm: x86: emulate APERF/MPERF registers

On 4/29/2020 1:46 PM, Li RongQing wrote:
> Guest kernel reports a fixed cpu frequency in /proc/cpuinfo,
> this is confused to user when turbo is enable, and aperf/mperf
> can be used to show current cpu frequency after 7d5905dc14a
> "(x86 / CPU: Always show current CPU frequency in /proc/cpuinfo)"
> so we should emulate aperf mperf to achieve it
> 
> the period of aperf/mperf in guest mode are accumulated as
> emulated value, and add per-VM knod to enable emulate mperfaperf
> 
> diff v1:
> 1. support AMD
> 2. support per-vm capability to enable
> 
[...]
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 851e9cc79930..1d157a8dba46 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -4310,6 +4310,12 @@ static int svm_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>   	case MSR_F10H_DECFG:
>   		msr_info->data = svm->msr_decfg;
>   		break;
> +	case MSR_IA32_MPERF:
> +		msr_info->data = vcpu->arch.v_mperf;
> +		break;
> +	case MSR_IA32_APERF:
> +		msr_info->data = vcpu->arch.v_aperf;
> +		break;
>   	default:
>   		return kvm_get_msr_common(vcpu, msr_info);
>   	}
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 91749f1254e8..b05e276e262b 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -1914,6 +1914,12 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>   		    !guest_cpuid_has(vcpu, X86_FEATURE_RDTSCP))
>   			return 1;
>   		goto find_shared_msr;
> +	case MSR_IA32_MPERF:
> +		msr_info->data = vcpu->arch.v_mperf;
> +		break;
> +	case MSR_IA32_APERF:
> +		msr_info->data = vcpu->arch.v_aperf;
> +		break;

They are same for both vmx and svm, you can put them in kvm_get_msr_common()

BTW, are those two MSR always readable regardless of guest's CPUID?

>   	default:
>   	find_shared_msr:
>   		msr = find_msr_entry(vmx, msr_info->index);