Re: CPU Lockups in KVM with deferred hrtimer rearming

Paolo Bonzini
2026-04-21T20:39:42Z

Il mar 21 apr 2026, 19:55 Sean Christopherson <seanjc@google.com> ha scritto:
>
> > > FWIW, VMX should work just like SVM if we clear VM_EXIT_ACK_INTR_ON_EXIT.
>
> Hell no.
>
> > I know. What's the point of that VM_EXIT_ACK_INTR_ON_EXIT exercise? Is
> > there any performance benefit or is it just used because it's there?
>
> There are performance benefits, and it preserves ordering [...]
> NMIs are unconditionally "acked" on VM-Exit.

Not that I disagree but...

> Even if performance is "fine", changing decades of fundamental KVM behavior is
> terrifying.

... it's not decades, ack on VM exit is actually relatively recent (10
years out 20 :)). The reason why it was introduced is another killer
for the idea, though. Posted interrupts require it, for some reason
only known to Intel.

Thanks,

Paolo