linux-kernel - Re: [PATCH v3 2/7] KVM: x86: nSVM: implement nested LBR virtualization

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Date:   Wed, 9 Mar 2022 14:00:09 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Maxim Levitsky <mlevitsk@...hat.com>, kvm@...r.kernel.org
Cc:     Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jim Mattson <jmattson@...gle.com>, x86@...nel.org,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Joerg Roedel <joro@...tes.org>, linux-kernel@...r.kernel.org,
        Wanpeng Li <wanpengli@...cent.com>
Subject: Re: [PATCH v3 2/7] KVM: x86: nSVM: implement nested LBR
 virtualization

On 3/1/22 15:36, Maxim Levitsky wrote:
> @@ -565,8 +565,19 @@ static void nested_vmcb02_prepare_save(struct vcpu_svm *svm, struct vmcb *vmcb12
>   		vmcb_mark_dirty(svm->vmcb, VMCB_DR);
>   	}
>   
> -	if (unlikely(svm->vmcb01.ptr->control.virt_ext & LBR_CTL_ENABLE_MASK))
> +	if (unlikely(svm->lbrv_enabled && (svm->nested.ctl.virt_ext & LBR_CTL_ENABLE_MASK))) {
> +
> +		/* Copy LBR related registers from vmcb12,
> +		 * but make sure that we only pick LBR enable bit from the guest.
> +		 */
> +
> +		svm_copy_lbrs(vmcb12, svm->vmcb);
> +		svm->vmcb->save.dbgctl &= LBR_CTL_ENABLE_MASK;

This should be checked against DEBUGCTL_RESERVED_BITS instead in 
__nested_vmcb_check_save; remember to add dbgctl to struct 
vmcb_save_area_cached too.

Paolo

> +		svm_update_lbrv(&svm->vcpu);
> +
> +	} else if (unlikely(svm->vmcb01.ptr->control.virt_ext & LBR_CTL_ENABLE_MASK)) {
>   		svm_copy_lbrs(svm->vmcb01.ptr, svm->vmcb);
> +	}
>   }