linux-kernel - Re: [PATCH v2 2/2] KVM: SVM: Use a separate vmcb for the nested L2 guest

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Date:   Fri, 13 Nov 2020 21:38:39 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Cathy Avery <cavery@...hat.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     vkuznets@...hat.com, wei.huang2@....com, mlevitsk@...hat.com
Subject: Re: [PATCH v2 2/2] KVM: SVM: Use a separate vmcb for the nested L2
 guest

On 13/11/20 18:58, Paolo Bonzini wrote:
> 
>> +    svm->nested.vmcb02->save.cr4 = svm->vmcb01->save.cr4;
> 
> I cannot understand this statement.

I wonder if it has something to do with

         unsigned long old_cr4 = to_svm(vcpu)->vmcb->save.cr4;

whereas vmx.c has

         unsigned long old_cr4 = vcpu->arch.cr4;

without this assignment, the old_cr4 would be taken from the last value 
stored in the vmcb02, instead of the current value for the vCPU.

In general uses of svm->vmcb01 (in svm.c especially) needs to be audited 
carefully.

Paolo