Re: [PATCH net-next 4/5] virtio_ring: introduce virtqueue_get_dma_premapped()

[Jason Wang <jasowang@redhat.com>]

On Tue, Jan 16, 2024 at 3:59 PM Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote:
>
> Introduce helper virtqueue_get_dma_premapped(), then the driver
> can know whether dma unmap is needed.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> ---
>  drivers/net/virtio/main.c       | 22 +++++++++-------------
>  drivers/net/virtio/virtio_net.h |  3 ---
>  drivers/virtio/virtio_ring.c    | 22 ++++++++++++++++++++++
>  include/linux/virtio.h          |  1 +
>  4 files changed, 32 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/net/virtio/main.c b/drivers/net/virtio/main.c
> index 186b2cf5d8fc..4fbf612da235 100644
> --- a/drivers/net/virtio/main.c
> +++ b/drivers/net/virtio/main.c
> @@ -483,7 +483,7 @@ static void *virtnet_rq_get_buf(struct virtnet_rq *rq, u32 *len, void **ctx)
>         void *buf;
>
>         buf = virtqueue_get_buf_ctx(rq->vq, len, ctx);
> -       if (buf && rq->do_dma)
> +       if (buf && virtqueue_get_dma_premapped(rq->vq))
>                 virtnet_rq_unmap(rq, buf, *len);
>
>         return buf;
> @@ -496,7 +496,7 @@ static void virtnet_rq_init_one_sg(struct virtnet_rq *rq, void *buf, u32 len)
>         u32 offset;
>         void *head;
>
> -       if (!rq->do_dma) {
> +       if (!virtqueue_get_dma_premapped(rq->vq)) {
>                 sg_init_one(rq->sg, buf, len);
>                 return;
>         }
> @@ -526,7 +526,7 @@ static void *virtnet_rq_alloc(struct virtnet_rq *rq, u32 size, gfp_t gfp)
>
>         head = page_address(alloc_frag->page);
>
> -       if (rq->do_dma) {
> +       if (virtqueue_get_dma_premapped(rq->vq)) {
>                 dma = head;
>
>                 /* new pages */
> @@ -580,12 +580,8 @@ static void virtnet_rq_set_premapped(struct virtnet_info *vi)
>         if (!vi->mergeable_rx_bufs && vi->big_packets)
>                 return;
>
> -       for (i = 0; i < vi->max_queue_pairs; i++) {
> -               if (virtqueue_set_dma_premapped(vi->rq[i].vq))
> -                       continue;
> -
> -               vi->rq[i].do_dma = true;
> -       }
> +       for (i = 0; i < vi->max_queue_pairs; i++)
> +               virtqueue_set_dma_premapped(vi->rq[i].vq);
>  }
>
>  static void free_old_xmit(struct virtnet_sq *sq, bool in_napi)
> @@ -1643,7 +1639,7 @@ static int add_recvbuf_small(struct virtnet_info *vi, struct virtnet_rq *rq,
>
>         err = virtqueue_add_inbuf_ctx(rq->vq, rq->sg, 1, buf, ctx, gfp);
>         if (err < 0) {
> -               if (rq->do_dma)
> +               if (virtqueue_get_dma_premapped(rq->vq))
>                         virtnet_rq_unmap(rq, buf, 0);
>                 put_page(virt_to_head_page(buf));
>         }
> @@ -1758,7 +1754,7 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi,
>         ctx = mergeable_len_to_ctx(len + room, headroom);
>         err = virtqueue_add_inbuf_ctx(rq->vq, rq->sg, 1, buf, ctx, gfp);
>         if (err < 0) {
> -               if (rq->do_dma)
> +               if (virtqueue_get_dma_premapped(rq->vq))
>                         virtnet_rq_unmap(rq, buf, 0);
>                 put_page(virt_to_head_page(buf));
>         }
> @@ -4007,7 +4003,7 @@ static void free_receive_page_frags(struct virtnet_info *vi)
>         int i;
>         for (i = 0; i < vi->max_queue_pairs; i++)
>                 if (vi->rq[i].alloc_frag.page) {
> -                       if (vi->rq[i].do_dma && vi->rq[i].last_dma)
> +                       if (virtqueue_get_dma_premapped(vi->rq[i].vq) && vi->rq[i].last_dma)
>                                 virtnet_rq_unmap(&vi->rq[i], vi->rq[i].last_dma, 0);
>                         put_page(vi->rq[i].alloc_frag.page);
>                 }
> @@ -4035,7 +4031,7 @@ static void virtnet_rq_free_unused_bufs(struct virtqueue *vq)
>         rq = &vi->rq[i];
>
>         while ((buf = virtqueue_detach_unused_buf(vq)) != NULL) {
> -               if (rq->do_dma)
> +               if (virtqueue_get_dma_premapped(rq->vq))
>                         virtnet_rq_unmap(rq, buf, 0);
>
>                 virtnet_rq_free_buf(vi, rq, buf);
> diff --git a/drivers/net/virtio/virtio_net.h b/drivers/net/virtio/virtio_net.h
> index b28a4d0a3150..066a2b9d2b3c 100644
> --- a/drivers/net/virtio/virtio_net.h
> +++ b/drivers/net/virtio/virtio_net.h
> @@ -115,9 +115,6 @@ struct virtnet_rq {
>
>         /* Record the last dma info to free after new pages is allocated. */
>         struct virtnet_rq_dma *last_dma;
> -
> -       /* Do dma by self */
> -       bool do_dma;
>  };
>
>  struct virtnet_info {
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 2c5089d3b510..9092bcdebb53 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -2905,6 +2905,28 @@ int virtqueue_set_dma_premapped(struct virtqueue *_vq)
>  }
>  EXPORT_SYMBOL_GPL(virtqueue_set_dma_premapped);
>
> +/**
> + * virtqueue_get_dma_premapped - get the vring premapped mode
> + * @_vq: the struct virtqueue we're talking about.
> + *
> + * Get the premapped mode of the vq.
> + *
> + * Returns bool for the vq premapped mode.
> + */
> +bool virtqueue_get_dma_premapped(struct virtqueue *_vq)
> +{
> +       struct vring_virtqueue *vq = to_vvq(_vq);
> +       bool premapped;
> +
> +       START_USE(vq);
> +       premapped = vq->premapped;
> +       END_USE(vq);

Why do we need to protect premapped like this? Is the user allowed to
change it on the fly?

Thanks