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

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Message-ID: <b03ec1e5447024f9f990377e2c28e84f@kernel.org>
Date:   Mon, 15 Mar 2021 09:20:58 +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 09:11, 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.

Thanks,

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