[PATCH] drm/virtio: fix vq wait_event condition

[Gerd Hoffmann]

On Tue, Apr 03, 2018 at 11:59:04AM +0200, Gerd Hoffmann wrote:
> Wait until we have enough space in the virt queue to actually queue up
> our request.  Avoids the guest spinning in case we have a non-zero
> amount of free entries but not enough for the request.

Ping airlied, can you please either pick it up or review so I can commit
myself?

thanks,
  Gerd

> Cc: stable at vger.kernel.org
> Reported-by: Alain Magloire <amagloire at blackberry.com>
> Signed-off-by: Gerd Hoffmann <kraxel at redhat.com>
> ---
>  drivers/gpu/drm/virtio/virtgpu_vq.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/virtio/virtgpu_vq.c b/drivers/gpu/drm/virtio/virtgpu_vq.c
> index 48e4f1df6e..020070d483 100644
> --- a/drivers/gpu/drm/virtio/virtgpu_vq.c
> +++ b/drivers/gpu/drm/virtio/virtgpu_vq.c
> @@ -293,7 +293,7 @@ static int virtio_gpu_queue_ctrl_buffer_locked(struct virtio_gpu_device *vgdev,
>  	ret = virtqueue_add_sgs(vq, sgs, outcnt, incnt, vbuf, GFP_ATOMIC);
>  	if (ret == -ENOSPC) {
>  		spin_unlock(&vgdev->ctrlq.qlock);
> -		wait_event(vgdev->ctrlq.ack_queue, vq->num_free);
> +		wait_event(vgdev->ctrlq.ack_queue, vq->num_free >= outcnt + incnt);
>  		spin_lock(&vgdev->ctrlq.qlock);
>  		goto retry;
>  	} else {
> @@ -368,7 +368,7 @@ static int virtio_gpu_queue_cursor(struct virtio_gpu_device *vgdev,
>  	ret = virtqueue_add_sgs(vq, sgs, outcnt, 0, vbuf, GFP_ATOMIC);
>  	if (ret == -ENOSPC) {
>  		spin_unlock(&vgdev->cursorq.qlock);
> -		wait_event(vgdev->cursorq.ack_queue, vq->num_free);
> +		wait_event(vgdev->cursorq.ack_queue, vq->num_free >= outcnt);
>  		spin_lock(&vgdev->cursorq.qlock);
>  		goto retry;
>  	} else {
> -- 
> 2.9.3
>