Re: [PATCH v3 3/4] KVM: arm64: GICv4.1: Restore VLPI's pending state to physical side

[Shenming Lu]

On 2021/3/12 20:02, Marc Zyngier wrote:
> On Fri, 12 Mar 2021 11:34:07 +0000,
> Shenming Lu <lushenming@xxxxxxxxxx> wrote:
>>
>> On 2021/3/12 19:10, Marc Zyngier wrote:
>>> On Fri, 12 Mar 2021 10:48:29 +0000,
>>> Shenming Lu <lushenming@xxxxxxxxxx> wrote:
>>>>
>>>> On 2021/3/12 17:05, Marc Zyngier wrote:
>>>>> On Thu, 11 Mar 2021 12:32:07 +0000,
>>>>> Shenming Lu <lushenming@xxxxxxxxxx> wrote:
>>>>>>
>>>>>> On 2021/3/11 17:14, Marc Zyngier wrote:
>>>>>>> On Wed, 27 Jan 2021 12:13:36 +0000,
>>>>>>> Shenming Lu <lushenming@xxxxxxxxxx> wrote:
>>>>>>>>
>>>>>>>> From: Zenghui Yu <yuzenghui@xxxxxxxxxx>
>>>>>>>>
>>>>>>>> When setting the forwarding path of a VLPI (switch to the HW mode),
>>>>>>>> we could also transfer the pending state from irq->pending_latch to
>>>>>>>> VPT (especially in migration, the pending states of VLPIs are restored
>>>>>>>> into kvm’s vgic first). And we currently send "INT+VSYNC" to trigger
>>>>>>>> a VLPI to pending.
>>>>>>>>
>>>>>>>> Signed-off-by: Zenghui Yu <yuzenghui@xxxxxxxxxx>
>>>>>>>> Signed-off-by: Shenming Lu <lushenming@xxxxxxxxxx>
>>>>>>>> ---
>>>>>>>>  arch/arm64/kvm/vgic/vgic-v4.c | 14 ++++++++++++++
>>>>>>>>  1 file changed, 14 insertions(+)
>>>>>>>>
>>>>>>>> diff --git a/arch/arm64/kvm/vgic/vgic-v4.c b/arch/arm64/kvm/vgic/vgic-v4.c
>>>>>>>> index ac029ba3d337..a3542af6f04a 100644
>>>>>>>> --- a/arch/arm64/kvm/vgic/vgic-v4.c
>>>>>>>> +++ b/arch/arm64/kvm/vgic/vgic-v4.c
>>>>>>>> @@ -449,6 +449,20 @@ int kvm_vgic_v4_set_forwarding(struct kvm *kvm, int virq,
>>>>>>>>  	irq->host_irq	= virq;
>>>>>>>>  	atomic_inc(&map.vpe->vlpi_count);
>>>>>>>>  
>>>>>>>> +	/* Transfer pending state */
>>>>>>>> +	if (irq->pending_latch) {
>>>>>>>> +		ret = irq_set_irqchip_state(irq->host_irq,
>>>>>>>> +					    IRQCHIP_STATE_PENDING,
>>>>>>>> +					    irq->pending_latch);
>>>>>>>> +		WARN_RATELIMIT(ret, "IRQ %d", irq->host_irq);
>>>>>>>> +
>>>>>>>> +		/*
>>>>>>>> +		 * Let it be pruned from ap_list later and don't bother
>>>>>>>> +		 * the List Register.
>>>>>>>> +		 */
>>>>>>>> +		irq->pending_latch = false;
>>>>>>>
>>>>>>> NAK. If the interrupt is on the AP list, it must be pruned from it
>>>>>>> *immediately*. The only case where it can be !pending and still on the
>>>>>>> AP list is in interval between sync and prune. If we start messing
>>>>>>> with this, we can't reason about the state of this list anymore.
>>>>>>>
>>>>>>> Consider calling vgic_queue_irq_unlock() here.
>>>>>>
>>>>>> Thanks for giving a hint, but it seems that vgic_queue_irq_unlock() only
>>>>>> queues an IRQ after checking, did you mean vgic_prune_ap_list() instead?
>>>>>
>>>>> No, I really mean vgic_queue_irq_unlock(). It can be used to remove
>>>>> the pending state from an interrupt, and drop it from the AP
>>>>> list. This is exactly what happens when clearing the pending state of
>>>>> a level interrupt, for example.
>>>>
>>>> Hi, I have gone through vgic_queue_irq_unlock more than once, but
>>>> still can't find the place in it to drop an IRQ from the AP
>>>> list... Did I miss something ?...  Or could you help to point it
>>>> out? Thanks very much for this!
>>>
>>> NO, you are right. I think this is a missing optimisation. Please call
>>> the function anyway, as that's what is required to communicate a
>>> change of state in general.>
>>> I'll have a think about it.
>>
>> Maybe we could call vgic_prune_ap_list() if (irq->vcpu &&
>> !vgic_target_oracle(irq)) in vgic_queue_irq_unlock()...
> 
> The locking is pretty ugly in this case, and I don't want to reparse
> the whole AP list. It is basically doing the same work as the
> insertion, but with a list_del() instead of a list_add()...

make sense..

Thanks,
Shenming

> 
> We can live without it for now.
> 
>> OK, I will retest this series and send a v4 soon. :-)
> 
> Thanks,
> 
> 	M.
>