linux-kernel - Re: [PATCH v6 6/8] virtio_vdpa: setup correct vq size with callbacks get_vq_num

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Date:   Mon, 25 Oct 2021 10:22:30 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Wu Zongyong <wuzongyong@...ux.alibaba.com>
Cc:     virtualization <virtualization@...ts.linux-foundation.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        mst <mst@...hat.com>, wei.yang1@...ux.alibaba.com
Subject: Re: [PATCH v6 6/8] virtio_vdpa: setup correct vq size with callbacks get_vq_num_{max,min}

On Fri, Oct 22, 2021 at 10:45 AM Wu Zongyong
<wuzongyong@...ux.alibaba.com> wrote:
>
> 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@...ux.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;
> +       }

I wonder under which case can we hit this?

Thanks

> +
>         /* Setup virtqueue callback */
>         cb.callback = virtio_vdpa_virtqueue_cb;
>         cb.private = info;
> --
> 2.31.1
>