linux-kernel - Re: [PATCH v2 06/15] KVM: vmx/pmu: Emulate MSR_ARCH_LBR

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Message-ID: <8f0fec41-d302-b261-ce5a-83692f1238b6@gmail.com>
Date:   Thu, 22 Dec 2022 19:09:45 +0800
From:   Like Xu <like.xu.linux@...il.com>
To:     Yang Weijiang <weijiang.yang@...el.com>
Cc:     kan.liang@...ux.intel.com, wei.w.wang@...el.com, seanjc@...gle.com,
        pbonzini@...hat.com, jmattson@...gle.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 06/15] KVM: vmx/pmu: Emulate MSR_ARCH_LBR_CTL for guest
 Arch LBR

On 25/11/2022 12:05 pm, Yang Weijiang wrote:
>   static int intel_pmu_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>   {
>   	struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
> @@ -377,6 +402,14 @@ static int intel_pmu_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>   	case MSR_ARCH_LBR_DEPTH:
>   		msr_info->data = lbr_desc->records.nr;
>   		return 0;
> +	case MSR_ARCH_LBR_CTL:
> +		if (!kvm_cpu_cap_has(X86_FEATURE_ARCH_LBR)) {
> +			WARN_ON_ONCE(!msr_info->host_initiated);

Why we need this warning even in the format of WARN_ON_ONCE() ?
And why not for MSR_ARCH_LBR_DEPTH msr ?

> +			msr_info->data = 0;
> +		} else {
> +			msr_info->data = vmcs_read64(GUEST_IA32_LBR_CTL);
> +		}
> +		return 0;