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

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Date:   Thu, 11 Mar 2021 20:32:07 +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 2021/3/11 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?

Thanks a lot for the comments! :-)
Shenming

> 
> Thanks,
> 
> 	M.
>