linux-kernel - Re: [PATCH 6/7] KVM: x86: Ignore benign host accesses to "unsupported" PEBS and BTS MSRs

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Date:   Mon, 13 Jun 2022 14:09:38 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Like Xu <likexu@...cent.com>
Subject: Re: [PATCH 6/7] KVM: x86: Ignore benign host accesses to
 "unsupported" PEBS and BTS MSRs

On Sat, Jun 11, 2022, Sean Christopherson wrote:
> @@ -4122,6 +4132,16 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  		msr_info->data = vcpu->arch.guest_fpu.xfd_err;
>  		break;
>  #endif
> +	case MSR_IA32_PEBS_ENABLE:
> +	case MSR_IA32_DS_AREA:
> +	case MSR_PEBS_DATA_CFG:
> +		if (kvm_pmu_is_valid_msr(vcpu, msr_info->index))
> +			return kvm_pmu_get_msr(vcpu, msr_info);
> +		/*
> +		 * Userspace is allowed to read MSRs that KVM reports as
> +		 * to-be-saved, even if an MSR isn't fully supported.
> +		 */
> +		return !msr_info->host_initiated;

Gah, this needs to set msr_info->data.

		/*
		 * Userspace is allowed to read MSRs that KVM reports as
		 * to-be-saved, even if an MSR isn't fully supported.
		 */
		if (!msr_info->host_initiated)
			return 1;

		msr_info->data = 0;

>  	default:
>  		if (kvm_pmu_is_valid_msr(vcpu, msr_info->index))
>  			return kvm_pmu_get_msr(vcpu, msr_info);
> -- 
> 2.36.1.476.g0c4daa206d-goog
>