On Mon, Sep 27, 2021, Paolo Bonzini wrote:
> On Mon, Sep 27, 2021 at 5:17 PM Christian Borntraeger
> <borntraeger@xxxxxxxxxx> wrote:
> > > So I think there are two possibilities that makes sense:
> > >
> > > * track what is using KVM_CAP_HALT_POLL, and make writes to halt_poll_ns follow that
> >
> > what about using halt_poll_ns for those VMs that did not uses KVM_CAP_HALT_POLL and the private number for those that did.
>
> Yes, that's what I meant. David pointed out that doesn't allow you to
> disable halt polling altogether, but for that you can always ask each
> VM's userspace one by one, or just not use KVM_CAP_HALT_POLL. (Also, I
> don't know about Google's usecase, but mine was actually more about
> using KVM_CAP_HALT_POLL to *disable* halt polling on some VMs!).
I kinda like the idea if special-casing halt_poll_ns=0, e.g. for testing or
in-the-field mitigation if halt-polling is broken. It'd be trivial to support, e.g.
@@ -3304,19 +3304,23 @@ void kvm_vcpu_halt(struct kvm_vcpu *vcpu)
update_halt_poll_stats(vcpu, start, poll_end, !waited);
if (halt_poll_allowed) {
+ max_halt_poll_ns = vcpu->kvm->max_halt_poll_ns;
+ if (!max_halt_poll_ns || !halt_poll_ns) <------ squish the max if halt_poll_ns==0
+ max_halt_poll_ns = halt_poll_ns;
+
if (!vcpu_valid_wakeup(vcpu)) {
shrink_halt_poll_ns(vcpu);
- } else if (vcpu->kvm->max_halt_poll_ns) {
+ } else if (max_halt_poll_ns) {
if (halt_ns <= vcpu->halt_poll_ns)
;
/* we had a long block, shrink polling */
else if (vcpu->halt_poll_ns &&
- halt_ns > vcpu->kvm->max_halt_poll_ns)
+ halt_ns > max_halt_poll_ns)
shrink_halt_poll_ns(vcpu);
/* we had a short halt and our poll time is too small */
- else if (vcpu->halt_poll_ns < vcpu->kvm->max_halt_poll_ns &&
- halt_ns < vcpu->kvm->max_halt_poll_ns)
- grow_halt_poll_ns(vcpu);
+ else if (vcpu->halt_poll_ns < max_halt_poll_ns &&
+ halt_ns < max_halt_poll_ns)
+ grow_halt_poll_ns(vcpu, max_halt_poll_ns);
} else {
vcpu->halt_poll_ns = 0;
}
