Re: [PATCH] KVM: SVM: Make sure GHCB is mapped before updating

[Tom Lendacky]

On 4/8/21 11:14 AM, Paolo Bonzini wrote:
> On 08/04/21 18:04, Tom Lendacky wrote:
>>>>> +       if (!err || !sev_es_guest(vcpu->kvm) ||
>>>>> !WARN_ON_ONCE(svm->ghcb))
>>>> This should be WARN_ON_ONCE(!svm->ghcb), otherwise you'll get the right
>>>> result, but get a stack trace immediately.
>>> Doh, yep.
>> Actually, because of the "or's", this needs to be:
>>
>> if (!err || !sev_es_guest(vcpu->kvm) || (sev_es_guest(vcpu->kvm) &&
>> WARN_ON_ONCE(!svm->ghcb)))
> 
> No, || cuts the right-hand side if the left-hand side is true.  So:
> 
> - if err == 0, the rest is not evaluated
> 
> - if !sev_es_guest(vcpu->kvm), WARN_ON_ONCE(!svm->ghcb) is not evaluated

That's what I was doing in my head, but I guess I need more coffee... :)

Thanks,
Tom

> 
> Paolo
>