netdev - Re: [PATCH V4 4/6] vhost_vdpa: implement IRQ offloading in vhost

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Date:   Tue, 28 Jul 2020 12:04:38 +0300
From:   Eli Cohen <eli@...lanox.com>
To:     Zhu Lingshan <lingshan.zhu@...el.com>
Cc:     jasowang@...hat.com, alex.williamson@...hat.com, mst@...hat.com,
        pbonzini@...hat.com, sean.j.christopherson@...el.com,
        wanpengli@...cent.com, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, kvm@...r.kernel.org, shahafs@...lanox.com,
        parav@...lanox.com
Subject: Re: [PATCH V4 4/6] vhost_vdpa: implement IRQ offloading in vhost_vdpa

On Tue, Jul 28, 2020 at 12:24:03PM +0800, Zhu Lingshan wrote:
>  
> +static void vhost_vdpa_setup_vq_irq(struct vhost_vdpa *v, int qid)
> +{
> +	struct vhost_virtqueue *vq = &v->vqs[qid];
> +	const struct vdpa_config_ops *ops = v->vdpa->config;
> +	struct vdpa_device *vdpa = v->vdpa;
> +	int ret, irq;
> +
> +	spin_lock(&vq->call_ctx.ctx_lock);
> +	irq = ops->get_vq_irq(vdpa, qid);
> +	if (!vq->call_ctx.ctx || irq == -EINVAL) {
> +		spin_unlock(&vq->call_ctx.ctx_lock);
> +		return;
> +	}
> +

If I understand correctly, this will cause these IRQs to be forwarded
directly to the VCPU, e.g. will be handled by the guest/qemu.
Does this mean that the host will not handle this interrupt? How does it
work in case on level triggered interrupts?

In the case of ConnectX, I need to execute some code to acknowledge the
interrupt.

Can you explain how this should be done?