linux-kernel - Re: [PATCH V2] KVM: SEV: Disable KVM_CAP_VM_COPY_ENC_CONTEXT

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Date:   Tue, 14 Sep 2021 19:12:20 +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>, stable@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2] 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. The destination VM is already checked for SEV and SEV-ES
> with sev_guest(), so this ioctl already fails if the destination is SEV
> enabled.
> 
> Enabling mirroring a VM or copying its encryption context with an SEV-ES
> VM is more involved and should happen in its own feature patch if that's
> needed. This is because the vCPUs of SEV-ES VMs need to be updated with
> LAUNCH_UPDATE_VMSA before LAUNCH_FINISH. This needs KVM changes because
> the mirror VM has all its SEV ioctls blocked and the original VM doesn't
> know about the mirrors vCPUs.

mirror's, or I guess mirrors'? :-)

> Fixes: 54526d1fd593 ("KVM: x86: Support KVM VMs sharing SEV context")
> 
> V2:
>  * Updated changelog with more information and added stable CC.

Nit, but this in the section ignored by git (below the ---) so that omitted from
the committed changelog.

> Signed-off-by: Peter Gonda <pgonda@...gle.com>
> Cc: Marc Orr <marcorr@...gle.com>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Sean Christopherson <seanjc@...gle.com>
> Cc: Nathan Tempelman <natet@...gle.com>
> Cc: Brijesh Singh <brijesh.singh@....com>
> Cc: kvm@...r.kernel.org
> Cc: stable@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org

Reviewed-by: Sean Christopherson <seanjc@...gle.com>

> ---

Git ignores stuff in this section.

>  arch/x86/kvm/svm/sev.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 75e0b21ad07c..8a279027425f 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -1728,7 +1728,7 @@ int svm_vm_copy_asid_from(struct kvm *kvm, unsigned int source_fd)
>  	source_kvm = source_kvm_file->private_data;
>  	mutex_lock(&source_kvm->lock);
>  
> -	if (!sev_guest(source_kvm)) {
> +	if (!sev_guest(source_kvm) || sev_es_guest(source_kvm)) {
>  		ret = -EINVAL;
>  		goto e_source_unlock;
>  	}
> -- 
> 2.33.0.309.g3052b89438-goog
>