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

[Heyi Guo]

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;