Re: [PATCH v2 06/15] KVM: vmx/pmu: Emulate MSR_ARCH_LBR_CTL for guest Arch LBR

[Like Xu <like.xu.linux@xxxxxxxxx>]

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;