linux-kernel - Re: [PATCH] KVM: nSVM: Optimize L12 to L2 vmcb.save copies

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Message-ID: <35b73239-56bd-8979-d9aa-1571eb73e94d@redhat.com>
Date:   Tue, 2 Mar 2021 15:20:11 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Cathy Avery <cavery@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        vkuznets@...hat.com, wei.huang2@....com
Subject: Re: [PATCH] KVM: nSVM: Optimize L12 to L2 vmcb.save copies

On 02/03/21 01:59, Sean Christopherson wrote:
>> +	svm->vmcb->save.cr2 = svm->vcpu.arch.cr2 = vmcb12->save.cr2;
> Same question for VMCB_CR2.

Besides the question of how much AMD processors actually use the clean 
bits (a quick test suggests "not much"), in this specific case I suspect 
that the check would be more expensive than the savings from a memory load.

Paolo