netdev - Re: [PATCH v5 06/22] virtio_ring: queue_reset: packed: support enable reset queue

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Date:   Wed, 16 Feb 2022 12:14:19 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Cc:     virtualization <virtualization@...ts.linux-foundation.org>,
        netdev <netdev@...r.kernel.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>, bpf@...r.kernel.org
Subject: Re: [PATCH v5 06/22] virtio_ring: queue_reset: packed: support enable
 reset queue

On Mon, Feb 14, 2022 at 4:14 PM Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
>
> The purpose of this patch is to make vring packed support re-enable reset
> vq.
>
> Based on whether the incoming vq passed by vring_setup_virtqueue() is
> NULL or not, distinguish whether it is a normal create virtqueue or
> re-enable a reset queue.
>
> When re-enable a reset queue, reuse the original callback, name, indirect.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> ---
>  drivers/virtio/virtio_ring.c | 29 ++++++++++++++++++-----------
>  1 file changed, 18 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 4639e1643c78..20659f7ca582 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -1683,7 +1683,8 @@ static struct virtqueue *vring_create_virtqueue_packed(
>         bool context,
>         bool (*notify)(struct virtqueue *),
>         void (*callback)(struct virtqueue *),
> -       const char *name)
> +       const char *name,
> +       struct virtqueue *_vq)
>  {
>         struct vring_virtqueue *vq;
>         struct vring_packed_desc *ring;
> @@ -1713,13 +1714,20 @@ static struct virtqueue *vring_create_virtqueue_packed(
>         if (!device)
>                 goto err_device;
>
> -       vq = kmalloc(sizeof(*vq), GFP_KERNEL);
> -       if (!vq)
> -               goto err_vq;
> +       if (_vq) {
> +               vq = to_vvq(_vq);
> +       } else {
> +               vq = kmalloc(sizeof(*vq), GFP_KERNEL);
> +               if (!vq)
> +                       goto err_vq;
> +
> +               vq->vq.callback = callback;
> +               vq->vq.name = name;
> +               vq->indirect = virtio_has_feature(vdev, VIRTIO_RING_F_INDIRECT_DESC) &&
> +                       !context;
> +       }

The code looks tricky. Except for the memory we don't even need to
touch any of the other attributes.

I'd suggest splitting out the vring allocation into a dedicated helper
that could be called by both vring_create_queue_XXX and the enable()
logic (and in the enable logic we don't even need to relocate if size
is not changed).

Thanks

>
> -       vq->vq.callback = callback;
>         vq->vq.vdev = vdev;
> -       vq->vq.name = name;
>         vq->vq.num_free = num;
>         vq->vq.index = index;
>         vq->we_own_ring = true;
> @@ -1736,8 +1744,6 @@ static struct virtqueue *vring_create_virtqueue_packed(
>         vq->last_add_time_valid = false;
>  #endif
>
> -       vq->indirect = virtio_has_feature(vdev, VIRTIO_RING_F_INDIRECT_DESC) &&
> -               !context;
>         vq->event = virtio_has_feature(vdev, VIRTIO_RING_F_EVENT_IDX);
>
>         if (virtio_has_feature(vdev, VIRTIO_F_ORDER_PLATFORM))
> @@ -1778,7 +1784,7 @@ static struct virtqueue *vring_create_virtqueue_packed(
>                 goto err_desc_extra;
>
>         /* No callback?  Tell other side not to bother us. */
> -       if (!callback) {
> +       if (!vq->vq.callback) {
>                 vq->packed.event_flags_shadow = VRING_PACKED_EVENT_FLAG_DISABLE;
>                 vq->packed.vring.driver->flags =
>                         cpu_to_le16(vq->packed.event_flags_shadow);
> @@ -1792,7 +1798,8 @@ static struct virtqueue *vring_create_virtqueue_packed(
>  err_desc_extra:
>         kfree(vq->packed.desc_state);
>  err_desc_state:
> -       kfree(vq);
> +       if (!_vq)
> +               kfree(vq);
>  err_vq:
>         vring_free_queue(vdev, event_size_in_bytes, device, device_event_dma_addr);
>  err_device:
> @@ -2317,7 +2324,7 @@ struct virtqueue *vring_setup_virtqueue(
>         if (virtio_has_feature(vdev, VIRTIO_F_RING_PACKED))
>                 return vring_create_virtqueue_packed(index, num, vring_align,
>                                 vdev, weak_barriers, may_reduce_num,
> -                               context, notify, callback, name);
> +                               context, notify, callback, name, vq);
>
>         return vring_create_virtqueue_split(index, num, vring_align,
>                         vdev, weak_barriers, may_reduce_num,
> --
> 2.31.0
>