[dpdk-stable] [PATCH] vhost: fix interrupt suppression for the split ring

[Tiwei Bie]

On Fri, Feb 22, 2019 at 04:13:50PM +0800, Jiayu Hu wrote:
> The VIRTIO_RING_F_EVENT_IDX feature of split ring might
> be broken, as the value of signalled_used is unpredictable
> after live migration or start up. This patch fixes it by
> using signalled_used_valid.

Seems you also need to invalidate the signalled_used in e.g.
set_vring_base, as signalled_used may not match last_used_idx
anymore e.g. when guest driver is reloaded.

> 
> In addition, this patch makes the VIRTIO_RING_F_EVENT_IDX
> implementation of split ring match kernel backend to suppress
> more interrupts.
> 
> Fixes: e37ff954405a ("vhost: support virtqueue interrupt/notification suppression")
> Cc: stable at dpdk.org
> 
> Signed-off-by: Jiayu Hu <jiayu.hu at intel.com>
> ---
>  lib/librte_vhost/vhost.h | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
> index fc31796..c4e5e34 100644
> --- a/lib/librte_vhost/vhost.h
> +++ b/lib/librte_vhost/vhost.h
> @@ -633,16 +633,20 @@ vhost_vring_call_split(struct virtio_net *dev, struct vhost_virtqueue *vq)
>  	if (dev->features & (1ULL << VIRTIO_RING_F_EVENT_IDX)) {
>  		uint16_t old = vq->signalled_used;
>  		uint16_t new = vq->last_used_idx;
> +		bool signalled_used_valid = vq->signalled_used_valid;
> +
> +		vq->signalled_used = new;
> +		vq->signalled_used_valid = true;
>  
>  		VHOST_LOG_DEBUG(VHOST_DATA, "%s: used_event_idx=%d, old=%d, new=%d\n",
>  			__func__,
>  			vhost_used_event(vq),
>  			old, new);
> -		if (vhost_need_event(vhost_used_event(vq), new, old)
> -			&& (vq->callfd >= 0)) {
> -			vq->signalled_used = vq->last_used_idx;
> +
> +		if ((vhost_need_event(vhost_used_event(vq), new, old) &&
> +					(vq->callfd >= 0)) ||
> +				unlikely(!signalled_used_valid))
>  			eventfd_write(vq->callfd, (eventfd_t) 1);
> -		}
>  	} else {
>  		/* Kick the guest if necessary. */
>  		if (!(vq->avail->flags & VRING_AVAIL_F_NO_INTERRUPT)
> -- 
> 2.7.4
>