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

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Date:   Tue, 14 Sep 2021 17:32:45 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Peter Gonda <pgonda@...gle.com>
Cc:     kvm@...r.kernel.org, Marc Orr <marcorr@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.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 Tue, Sep 14, 2021, Peter Gonda wrote:
> Copying an ASID into new vCPUs will not work for SEV-ES since the vCPUs
> VMSAs need to be setup and measured before SEV_LAUNCH_FINISH. Return an
> error if a users tries to KVM_CAP_VM_COPY_ENC_CONTEXT_FROM from an
> SEV-ES guest.

What happens if userspace does KVM_CAP_VM_COPY_ENC_CONTEXT_FROM before the source
has created vCPUs, i.e. before it has done SEV_LAUNCH_FINISH?

Might be worth noting that the destination cannot be an SEV guest, and therefore
can't be an SEV-ES guest either.

> Fixes: 54526d1fd593 ("KVM: x86: Support KVM VMs sharing SEV context")

Cc: stable@...r.kernel.org