Re: [PATCH 12/13] KVM: x86: Replace late check_nested_events() hack with more precise fix

From: Sean Christopherson
Date: Tue Apr 28 2020 - 18:20:13 EST


On Tue, Apr 28, 2020 at 03:12:51PM -0700, Jim Mattson wrote:
> On Wed, Apr 22, 2020 at 7:26 PM Sean Christopherson
> <sean.j.christopherson@xxxxxxxxx> wrote:
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index 7c49a7dc601f..d9d6028a77e0 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -7755,24 +7755,10 @@ static int inject_pending_event(struct kvm_vcpu *vcpu)
> > --vcpu->arch.nmi_pending;
> > vcpu->arch.nmi_injected = true;
> > kvm_x86_ops.set_nmi(vcpu);
> > - } else if (kvm_cpu_has_injectable_intr(vcpu)) {
> > - /*
> > - * Because interrupts can be injected asynchronously, we are
> > - * calling check_nested_events again here to avoid a race condition.
> > - * See https://lkml.org/lkml/2014/7/2/60 for discussion about this
> > - * proposal and current concerns. Perhaps we should be setting
> > - * KVM_REQ_EVENT only on certain events and not unconditionally?
> > - */
> > - if (is_guest_mode(vcpu) && kvm_x86_ops.check_nested_events) {
> > - r = kvm_x86_ops.check_nested_events(vcpu);
> > - if (r != 0)
> > - return r;
> > - }
> > - if (kvm_x86_ops.interrupt_allowed(vcpu)) {
> > - kvm_queue_interrupt(vcpu, kvm_cpu_get_interrupt(vcpu),
> > - false);
> > - kvm_x86_ops.set_irq(vcpu);
> > - }
> > + } else if (kvm_cpu_has_injectable_intr(vcpu) &&
> > + kvm_x86_ops.interrupt_injection_allowed(vcpu)) {
> > + kvm_queue_interrupt(vcpu, kvm_cpu_get_interrupt(vcpu), false);
> > + kvm_x86_ops.set_irq(vcpu);
> > }
> So, that's what this mess was all about! Well, this certainly looks better.

Right? I can't count the number of times I've looked at this code and
wondered what the hell it was doing.

Side topic, I just realized you're reviewing my original series. Paolo
commandeered it to extend it to SVM. https://patchwork.kernel.org/cover/11508679/