linux-kernel - Re: [PATCH 07/12] KVM: x86: SEV: Treat C-bit as legal GPA bit regardless of vCPU mode

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Message-ID: <f1d2f324-d309-5039-f4f6-bbec9220259f@redhat.com>
Date:   Thu, 4 Feb 2021 11:34:15 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
Cc:     "jmattson@...gle.com" <jmattson@...gle.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "vkuznets@...hat.com" <vkuznets@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "thomas.lendacky@....com" <thomas.lendacky@....com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "brijesh.singh@....com" <brijesh.singh@....com>,
        "wanpengli@...cent.com" <wanpengli@...cent.com>
Subject: Re: [PATCH 07/12] KVM: x86: SEV: Treat C-bit as legal GPA bit
 regardless of vCPU mode

On 04/02/21 03:19, Sean Christopherson wrote:
> Ah, took me a few minutes, but I see what you're saying.  LAM will introduce
> bits that are repurposed for CR3, but not generic GPAs.  And, the behavior is
> based on CPU support, so it'd make sense to have a mask cached in vcpu->arch
> as opposed to constantly generating it on the fly.
> 
> Definitely agree that having a separate cr3_lm_rsvd_bits or whatever is the
> right way to go when LAM comes along.  Not sure it's worth keeping a duplicate
> field in the meantime, though it would avoid a small amount of thrash.

We don't even know if the cr3_lm_rsvd_bits would be a field in 
vcpu->arch, or rather computed on the fly.  So renaming the field in 
vcpu->arch seems like the simplest thing to do now.

Paolo