linux-kernel - Re: [PATCH v4 5/6] KVM: arm64: GICv4.1: Restore VLPI pending state to physical side

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Date:   Mon, 15 Mar 2021 17:25:13 +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 v4 5/6] KVM: arm64: GICv4.1: Restore VLPI pending state to
 physical side

On 2021/3/15 17:20, Marc Zyngier wrote:
> On 2021-03-15 09:11, Shenming Lu wrote:
>> On 2021/3/15 16:30, Marc Zyngier wrote:
>>> On 2021-03-13 08:38, Shenming Lu wrote:
>>>> From: Zenghui Yu <yuzenghui@...wei.com>
>>>>
>>>> When setting the forwarding path of a VLPI (switch to the HW mode),
>>>> we can 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 | 18 ++++++++++++++++++
>>>>  1 file changed, 18 insertions(+)
>>>>
>>>> diff --git a/arch/arm64/kvm/vgic/vgic-v4.c b/arch/arm64/kvm/vgic/vgic-v4.c
>>>> index ac029ba3d337..3b82ab80c2f3 100644
>>>> --- a/arch/arm64/kvm/vgic/vgic-v4.c
>>>> +++ b/arch/arm64/kvm/vgic/vgic-v4.c
>>>> @@ -449,6 +449,24 @@ 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) {
>>>> +        unsigned long flags;
>>>> +
>>>> +        ret = irq_set_irqchip_state(irq->host_irq,
>>>> +                        IRQCHIP_STATE_PENDING,
>>>> +                        irq->pending_latch);
>>>> +        WARN_RATELIMIT(ret, "IRQ %d", irq->host_irq);
>>>> +
>>>> +        /*
>>>> +         * Clear pending_latch and communicate this state
>>>> +         * change via vgic_queue_irq_unlock.
>>>> +         */
>>>> +        raw_spin_lock_irqsave(&irq->irq_lock, flags);
>>>> +        irq->pending_latch = false;
>>>> +        vgic_queue_irq_unlock(kvm, irq, flags);
>>>> +    }
>>>> +
>>>>  out:
>>>>      mutex_unlock(&its->its_lock);
>>>>      return ret;
>>>
>>> The read side of the pending state isn't locked, but the write side is.
>>> I'd rather you lock the whole sequence for peace of mind.
>>
>> Did you mean to lock before emitting the mapping request, Or just before reading
>> the pending state?
> 
> Just before reading the pending state, so that we can't get a concurrent
> modification of that state while we make the interrupt pending in the VPT
> and clearing it in the emulation.

Get it. I will correct it right now.

Thanks,
Shenming

> 
> Thanks,
> 
>         M.