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

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Message-ID: <4f37549dcc5d3dd59a92bc94f2f0b59b@kernel.org>
Date:   Mon, 15 Mar 2021 09:30:06 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Shenming Lu <lushenming@...wei.com>
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 2021-03-15 09:25, Shenming Lu wrote:
> 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.

Please hold off sending a new version for a few days. My inbox is 
exploding...

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...