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

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Message-ID: <df4b939d-27c1-be84-ea7e-327251958cde@huawei.com>
Date:   Fri, 12 Mar 2021 19:34:07 +0800
From:   Shenming Lu <lushenming@...wei.com>
To:     Marc Zyngier <maz@...nel.org>
CC:     Eric Auger <eric.auger@...hat.com>, Will Deacon <will@...nel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <kvmarm@...ts.cs.columbia.edu>, <kvm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>,
        "Lorenzo Pieralisi" <lorenzo.pieralisi@....com>,
        <wanghaibin.wang@...wei.com>, <yuzenghui@...wei.com>
Subject: Re: [PATCH v3 3/4] KVM: arm64: GICv4.1: Restore VLPI's pending state
 to physical side

On 2021/3/12 19:10, Marc Zyngier wrote:
> On Fri, 12 Mar 2021 10:48:29 +0000,
> Shenming Lu <lushenming@...wei.com> wrote:
>>
>> On 2021/3/12 17:05, Marc Zyngier wrote:
>>> On Thu, 11 Mar 2021 12:32:07 +0000,
>>> Shenming Lu <lushenming@...wei.com> wrote:
>>>>
>>>> On 2021/3/11 17:14, Marc Zyngier wrote:
>>>>> On Wed, 27 Jan 2021 12:13:36 +0000,
>>>>> Shenming Lu <lushenming@...wei.com> wrote:
>>>>>>
>>>>>> From: Zenghui Yu <yuzenghui@...wei.com>
>>>>>>
>>>>>> 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@...wei.com>
>>>>>> Signed-off-by: Shenming Lu <lushenming@...wei.com>
>>>>>> ---
>>>>>>  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()...

OK, I will retest this series and send a v4 soon. :-)

Thanks,
Shenming

> 
> Thanks,
> 
> 	M.
>