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

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Message-ID: <d9047922808df340feca2f257cfb8a3d@kernel.org>
Date:   Mon, 15 Mar 2021 08:30:52 +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 2021-03-13 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.

Thanks,

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