Re: [PATCH v2 3/5] KVM: SVM: fix race between interrupt delivery and AVIC inhibition

[Paolo Bonzini]

On 1/5/22 12:03, Maxim Levitsky wrote:
> > > -	if (!vcpu->arch.apicv_active)
> > > -		return -1;
> > > -
> > > +	/*
> > > +	 * Below, we have to handle anyway the case of AVIC being disabled
> > > +	 * in the middle of this function, and there is hardly any overhead
> > > +	 * if AVIC is disabled.  So, we do not bother returning -1 and handle
> > > +	 * the kick ourselves for disabled APICv.
> > Hmm, my preference would be to keep the "return -1" even though apicv_active must
> > be rechecked.  That would help highlight that returning "failure" after this point
> > is not an option as it would result in kvm_lapic_set_irr() being called twice.
> I don't mind either - this will fix the tracepoint I recently added to report the
> number of interrupts that were delivered by AVIC/APICv - with this patch,
> all of them count as such.

The reasoning here is that, unlike VMX, we have to react anyway to 
vcpu->arch.apicv_active becoming false halfway through the function.

Removing the early return means that there's one less case of load 
(mis)reordering that the reader has to check.  So I really would prefer 
to remove it.

Agreed with the other feedback.

Paolo