linux-kernel - Re: [PATCH] KVM: SEV: Disable KVM_CAP_VM_COPY_ENC_CONTEXT

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Date:   Wed, 15 Sep 2021 10:44:09 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Peter Gonda <pgonda@...gle.com>
Cc:     kvm list <kvm@...r.kernel.org>, Marc Orr <marcorr@...gle.com>,
        Nathan Tempelman <natet@...gle.com>,
        Brijesh Singh <brijesh.singh@....com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: SEV: Disable KVM_CAP_VM_COPY_ENC_CONTEXT_FROM for
 SEV-ES

On 14/09/21 20:49, Sean Christopherson wrote:
> On Tue, Sep 14, 2021, Peter Gonda wrote:
>> I do not think so. You cannot call KVM_SEV_LAUNCH_UPDATE_VMSA on the mirror
>> because svm_mem_enc_op() blocks calls from the mirror. So either you have to
>> update vmsa from the mirror or have the original VM read through its mirror's
>> vCPUs when calling KVM_SEV_LAUNCH_UPDATE_VMSA. Not sure which way is better
>> but I don't see a way to do this without updating KVM.
> 
> Ah, right, I forgot all of the SEV ioctls are blocked on the mirror.  Put something
> to that effect into the changelog to squash any argument about whether or not this
> is the correct KVM behavior.

Indeed, at least KVM_SEV_LAUNCH_UPDATE_VMSA would have to be allowed in 
the mirror VM.  Do you think anything else would be necessary?

Paolo