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

[Heyi Guo <guoheyi@huawei.com>]

On 2019/3/29 18:54, Marc Zyngier wrote:
> On 29/03/2019 09:19, Heyi Guo wrote:
>> 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.
>
> Thanks for testing, much appreciated.
>
>> Just a minor comment: how about replacing /vcpu->arch.vgic_cpu./ with
>> /vgic_cpu->/ in the lock/unlock code line, to reduce some words?
> Well, as I said, the patch is wrong in other ways, so I wouldn't bother
> with that. It only serves as a test for my theory.
Sure, I hadn't caught the last sentence of your previous mail...
>
> I think I'm slowly warming up to you initial proposal to hook things
> into the PROPBASER/PENDBASER registers, as the LPIs do have a life
> outside of the ITS itself.
>
> I'll try to respin something next week.
Thanks,

Heyi

>
> Thanks,
>
> 	M.
>
>> 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;
>>>>
>>>
>>>
>>> .
>>>
>>
>