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

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Message-ID: <81fbadda-0489-ffc3-cb38-08e89871ec95@huawei.com>
Date:   Mon, 15 Mar 2021 17:11:34 +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 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?

Thanks,
Shenming

> 
> Thanks,
> 
>         M.