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

From: Heyi Guo
Date: Fri Mar 29 2019 - 05:20:05 EST

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?



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
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

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.



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;