linux-kernel - Re: [PATCH V2] KVM: SEV: Update SEV-ES shutdown intercepts with more metadata

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Date:   Wed, 6 Sep 2023 14:18:21 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Peter Gonda <pgonda@...gle.com>, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Joerg Roedel <joro@...tes.org>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2] KVM: SEV: Update SEV-ES shutdown intercepts with more
 metadata

On 9/6/23 10:14, Peter Gonda wrote:
> Currently if an SEV-ES VM shuts down userspace sees KVM_RUN struct with

s/down userspace/down, userspace/

> only the INVALID_ARGUMENT. This is a very limited amount of information
> to debug the situation. Instead KVM can return a
> KVM_EXIT_SHUTDOWN to alert userspace the VM is shutting down and
> is not usable any further.
> 
> Signed-off-by: Peter Gonda <pgonda@...gle.com>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Sean Christopherson <seanjc@...gle.com>
> Cc: Tom Lendacky <thomas.lendacky@....com>
> Cc: Joerg Roedel <joro@...tes.org>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: x86@...nel.org
> Cc: kvm@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> 
> ---
>   arch/x86/kvm/svm/svm.c | 8 +++++---
>   1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 956726d867aa..cecf6a528c9b 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -2131,12 +2131,14 @@ static int shutdown_interception(struct kvm_vcpu *vcpu)
>   	 * The VM save area has already been encrypted so it
>   	 * cannot be reinitialized - just terminate.
>   	 */
> -	if (sev_es_guest(vcpu->kvm))
> -		return -EINVAL;
> +	if (sev_es_guest(vcpu->kvm)) {
> +		kvm_run->exit_reason = KVM_EXIT_SHUTDOWN;
> +		return 0;
> +	}

Just a nit... feel free to ignore, but, since KVM_EXIT_SHUTDOWN is also 
set at the end of the function and I don't think kvm_vcpu_reset() clears 
the value from kvm_run, you could just set kvm_run->exit_reason on entry 
and just return 0 early for an SEV-ES guest.

Overall, though:

Acked-by: Tom Lendacky <thomas.lendacky@....com>

Thanks,
Tom

>   
>   	/*
>   	 * VMCB is undefined after a SHUTDOWN intercept.  INIT the vCPU to put
> -	 * the VMCB in a known good state.  Unfortuately, KVM doesn't have
> +	 * the VMCB in a known good state.  Unfortunately, KVM doesn't have
>   	 * KVM_MP_STATE_SHUTDOWN and can't add it without potentially breaking
>   	 * userspace.  At a platform view, INIT is acceptable behavior as
>   	 * there exist bare metal platforms that automatically INIT the CPU