Re: [PATCH v5 6/8] virtio_vdpa: setup correct vq size with callbacks get_vq_num_{max,min}

[Jason Wang <jasowang@redhat.com>]

在 2021/10/15 下午3:14, Wu Zongyong 写道:
> For the devices which implement the get_vq_num_min callback, the driver
> should not negotiate with virtqueue size with the backend vdpa device if
> the value returned by get_vq_num_min equals to the value returned by
> get_vq_num_max.
> This is useful for vdpa devices based on legacy virtio specfication.
>
> Signed-off-by: Wu Zongyong <wuzongyong@linux.alibaba.com>
> ---
>   drivers/virtio/virtio_vdpa.c | 21 ++++++++++++++++-----
>   1 file changed, 16 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/virtio/virtio_vdpa.c b/drivers/virtio/virtio_vdpa.c
> index 72eaef2caeb1..e42ace29daa1 100644
> --- a/drivers/virtio/virtio_vdpa.c
> +++ b/drivers/virtio/virtio_vdpa.c
> @@ -145,7 +145,8 @@ virtio_vdpa_setup_vq(struct virtio_device *vdev, unsigned int index,
>   	/* Assume split virtqueue, switch to packed if necessary */
>   	struct vdpa_vq_state state = {0};
>   	unsigned long flags;
> -	u32 align, num;
> +	u32 align, max_num, min_num = 0;
> +	bool may_reduce_num = true;
>   	int err;
>   
>   	if (!name)
> @@ -163,22 +164,32 @@ virtio_vdpa_setup_vq(struct virtio_device *vdev, unsigned int index,
>   	if (!info)
>   		return ERR_PTR(-ENOMEM);
>   
> -	num = ops->get_vq_num_max(vdpa);
> -	if (num == 0) {
> +	max_num = ops->get_vq_num_max(vdpa);
> +	if (max_num == 0) {
>   		err = -ENOENT;
>   		goto error_new_virtqueue;
>   	}
>   
> +	if (ops->get_vq_num_min)
> +		min_num = ops->get_vq_num_min(vdpa);
> +
> +	may_reduce_num = (max_num == min_num) ? false : true;
> +
>   	/* Create the vring */
>   	align = ops->get_vq_align(vdpa);
> -	vq = vring_create_virtqueue(index, num, align, vdev,
> -				    true, true, ctx,
> +	vq = vring_create_virtqueue(index, max_num, align, vdev,
> +				    true, may_reduce_num, ctx,
>   				    virtio_vdpa_notify, callback, name);
>   	if (!vq) {
>   		err = -ENOMEM;
>   		goto error_new_virtqueue;
>   	}
>   
> +	if (virtqueue_get_vring_size(vq) < min_num) {
> +		err = -EINVAL;
> +		goto err_vq;
> +	}


Under which condition can we hit this error?

Thanks


> +
>   	/* Setup virtqueue callback */
>   	cb.callback = virtio_vdpa_virtqueue_cb;
>   	cb.private = info;