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SubjectRe: [PATCH V2] KVM: SEV: Update SEV-ES shutdown intercepts with more metadata
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On 9/6/23 15:26, Sean Christopherson wrote:
> On Wed, Sep 06, 2023, Tom Lendacky wrote:
>> On 9/6/23 15:11, Sean Christopherson wrote:
>>> On Wed, Sep 06, 2023, Tom Lendacky wrote:
>>>> On 9/6/23 10:14, Peter Gonda wrote:
>>>>> 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.
>>>
>>> kvm_run is writable by userspace though, so KVM can't rely on kvm_run->exit_reason
>>> for correctness.
>>>
>>> And IIUC, the VMSA is also toast, i.e. doing anything other than marking the VM
>>> dead is futile, no?
>>
>> I was just saying that "kvm_run->exit_reason = KVM_EXIT_SHUTDOWN;" is in the
>> shutdown_interception() function twice now (at both exit points of the
>> function) and can probably just be moved to the top of the function and be
>> common for both exit points, now, right?
>>
>> I'm not saying to get rid of it, just set it sooner.
>
> Ah, I thought you were saying bail early from kvm_vcpu_reset(). I agree that not
> having completely split logic would be ideal. What about this?
>
> /*
> * VMCB is undefined after a SHUTDOWN intercept. INIT the vCPU to put
> * the VMCB in a known good state. Unfortuately, 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
> * in response to shutdown.
> *
> * The VM save area for SEV-ES guests has already been encrypted so it
> * cannot be reinitialized, i.e. synthesizing INIT is futile.
> */
> if (!sev_es_guest(vcpu->kvm)) {
> clear_page(svm->vmcb);
> kvm_vcpu_reset(vcpu, true);
> }
>
> kvm_run->exit_reason = KVM_EXIT_SHUTDOWN;
> return 0;

That looks good to me!

Thanks,
Tom

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