Re: [PATCH 5/6] KVM: x86: never clear irr_pending in kvm_apic_update_apicv

Paolo Bonzini
2021-12-10T13:03:21Z

On 12/10/21 13:47, Maxim Levitsky wrote:
> If we scan vIRR here and see no bits, and*then* disable AVIC,
> there is a window where the they could legit be turned on without any cpu errata,
> and we will not have irr_pending == true, and thus the following
> KVM_REQ_EVENT will make no difference.

Right.

> Not touching irr_pending and letting just the KVM_REQ_EVENT do the work
> will work too,

Yeah, I think that's preferrable. irr_pending == true is a conservative
setting that works; irr_pending will be evaluated again on the first
call to apic_clear_irr and that's enough.

With that justification, you don't need to reorder the call to
kvm_apic_update_apicv to be after kvm_x86_refresh_apicv_exec_ctrl.

Paolo

and if the avic errata is present, reduce slightly
> the chances of it happening.