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

[Marc Zyngier]

[Please do not send HTML emails]

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. 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,

	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;

-- 
Jazz is not dead. It just smells funny...