Re: Unexpected interrupt received in Guest OS when booting after "system_reset"

[Heyi Guo]

Hi Marc,

The patch works. I tested for 1.5 hour and 52 VM resets. There were 16 times that a virtual LPI left in the ap_list (seen by an additional printk) during reset and we never saw "Unexpected interrupt received" any more.

Just a minor comment: how about replacing /vcpu->arch.vgic_cpu./ with /vgic_cpu->/ in the lock/unlock code line, to reduce some words?

Thanks,

Heyi

On 2019/3/29 9:19, Heyi Guo wrote:
> On 2019/3/29 1:18, Marc Zyngier wrote:
> > [Please do not send HTML emails]
> Sorry; will keep in mind next time :)
> > On 28/03/2019 15:44, Heyi Guo wrote:
> > > Hi Marc and Christoffer,
> > >
> > > When we issue "system_reset" from qemu monitor to a running VM, guest
> > > Linux will occasionally get "Unexpected interrupt" after rebooting, with
> > > kernel message at the bottom.
> > >
> > > After some investigation, we found it might be caused by the
> > > preservation of virtual LPI during system reset: it seems the virtual
> > > LPI remains in the ap_list during VM reset, as well as its "enabled" and
> > > "pending_latch" status, and this causes the virtual LPI to be injected
> > > wrongly after VCPU reboots and enables interrupt.
> > >
> > > We propose to clear "enabled" flag of virtual LPI when PROPBASER (or
> > > GICR_CTRL) of virtual GICR is written to 0, and update virtual LPI
> > > properties when GICR_CTRL.enableLPIs is set to 1 again.
> > >
> > > Any advice? Or did we miss something?
> > We're clearly missing a trick here, but I'm not convinced of your
> > approach.
> To be honest, we were not fully convinced by ourselves either. I was worrying about guest switching GICR_CTRL or GICR_PROPBASER at runtime which probably causes issue for our rough approach.
>
> > What should happend is that the redistributors should be reset
> > as well, and that this should recall any LPI that has been made pending.
> > Unfortunately, we don't seem to have such code in place, which is
> > embarrassing.
> >
> > Can you give the following, untested patch a go? It isn't right either,
> > but it should have the right effect. If you confirm that it solves your
> > problem, we can look at adding the right hooks...
> Thanks, I'll test this and get back to you.
> Heyi
>
> > Thanks,
> >
> >     M.
> >
> > diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
> > index ab3f47745d9c..bd9a9250f323 100644
> > --- a/virt/kvm/arm/vgic/vgic-its.c
> > +++ b/virt/kvm/arm/vgic/vgic-its.c
> > @@ -2403,8 +2403,32 @@ static int vgic_its_commit_v0(struct vgic_its *its)
> >       return 0;
> >   }
> >   +static void vgic_nuke_pending_lpis(struct kvm_vcpu *vcpu)
> > +{
> > +    struct vgic_cpu *vgic_cpu = &vcpu->arch.vgic_cpu;
> > +    struct vgic_irq *irq, *tmp;
> > +    unsigned long flags;
> > +
> > + raw_spin_lock_irqsave(&vcpu->arch.vgic_cpu.ap_list_lock, flags);
> > +
> > +    list_for_each_entry_safe(irq, tmp, &vgic_cpu->ap_list_head, ap_list) {
> > +        if (irq->intid >= VGIC_MIN_LPI) {
> > +            list_del(&irq->ap_list);
> > +            vgic_put_irq(vcpu->kvm, irq);
> > +        }
> > +    }
> > +
> > + raw_spin_unlock_irqrestore(&vcpu->arch.vgic_cpu.ap_list_lock, flags);
> > +}
> > +
> >   static void vgic_its_reset(struct kvm *kvm, struct vgic_its *its)
> >   {
> > +    struct kvm_vcpu *vcpu;
> > +    int c;
> > +
> > +    kvm_for_each_vcpu(c, vcpu, kvm)
> > +        vgic_nuke_pending_lpis(vcpu);
> > +
> >       /* We need to keep the ABI specific field values */
> >       its->baser_coll_table &= ~GITS_BASER_VALID;
> >       its->baser_device_table &= ~GITS_BASER_VALID;
>
>
>
> .