[PATCH vhost 17/17] virtio_net: sq support premapped mode

[Jason Wang]

On Tue, Jan 30, 2024 at 7:43 PM Xuan Zhuo <xuanzhuo at linux.alibaba.com> wrote:
>
> If the xsk is enabling, the xsk tx will share the send queue.
> But the xsk requires that the send queue use the premapped mode.
> So the send queue must support premapped mode.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo at linux.alibaba.com>
> ---
>  drivers/net/virtio_net.c | 167 ++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 163 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 226ab830870e..cf0c67380b07 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -46,6 +46,7 @@ module_param(napi_tx, bool, 0644);
>  #define VIRTIO_XDP_REDIR       BIT(1)
>
>  #define VIRTIO_XDP_FLAG        BIT(0)
> +#define VIRTIO_DMA_FLAG        BIT(1)
>
>  /* RX packet size EWMA. The average packet size is used to determine the packet
>   * buffer size when refilling RX rings. As the entire RX ring may be refilled
> @@ -140,6 +141,21 @@ struct virtnet_rq_dma {
>         u16 need_sync;
>  };
>
> +struct virtnet_sq_dma {
> +       union {
> +               struct virtnet_sq_dma *next;
> +               void *data;
> +       };
> +       dma_addr_t addr;
> +       u32 len;
> +       bool is_tail;
> +};
> +
> +struct virtnet_sq_dma_head {
> +       struct virtnet_sq_dma *free;
> +       struct virtnet_sq_dma *head;

Any reason the head must be a pointer instead of a simple index?

> +};
> +
>  /* Internal representation of a send virtqueue */
>  struct send_queue {
>         /* Virtqueue associated with this send _queue */
> @@ -159,6 +175,8 @@ struct send_queue {
>
>         /* Record whether sq is in reset state. */
>         bool reset;
> +
> +       struct virtnet_sq_dma_head dmainfo;
>  };
>
>  /* Internal representation of a receive virtqueue */
> @@ -348,6 +366,131 @@ static struct xdp_frame *ptr_to_xdp(void *ptr)
>         return (struct xdp_frame *)((unsigned long)ptr & ~VIRTIO_XDP_FLAG);
>  }
>
> +static inline void *virtnet_sq_unmap(struct send_queue *sq, void *data)
> +{
> +       struct virtnet_sq_dma *head, *tail;
> +
> +       if (!((unsigned long)data & VIRTIO_DMA_FLAG))
> +               return data;
> +
> +       head = (void *)((unsigned long)data & ~VIRTIO_DMA_FLAG);
> +
> +       tail = head;
> +
> +       while (true) {
> +               virtqueue_dma_unmap_page_attrs(sq->vq, tail->addr, tail->len,
> +                                              DMA_TO_DEVICE, 0);
> +
> +               if (tail->is_tail)
> +                       break;
> +
> +               tail = tail->next;
> +       }
> +
> +       data = tail->data;
> +       tail->is_tail = false;
> +
> +       tail->next = sq->dmainfo.free;
> +       sq->dmainfo.free = head;
> +
> +       return data;
> +}
> +
> +static void *virtnet_sq_dma_splice(struct send_queue *sq,
> +                                  struct virtnet_sq_dma *head,
> +                                  struct virtnet_sq_dma *tail,
> +                                  void *data)
> +{
> +       sq->dmainfo.free = tail->next;
> +
> +       tail->is_tail = true;
> +       tail->data = data;
> +
> +       head = (void *)((unsigned long)head | VIRTIO_DMA_FLAG);
> +
> +       return head;
> +}
> +
> +static struct virtnet_sq_dma *virtnet_sq_map_sg(struct send_queue *sq, int nents, void *data)
> +{
> +       struct virtnet_sq_dma *head, *tail, *p;
> +       struct scatterlist *sg;
> +       dma_addr_t addr;
> +       int i;
> +
> +       head = sq->dmainfo.free;
> +       p = head;
> +
> +       tail = NULL;
> +
> +       for_each_sg(sq->sg, sg, nents, i) {
> +               addr = virtqueue_dma_map_page_attrs(sq->vq, sg_page(sg),
> +                                                   sg->offset, sg->length,
> +                                                   DMA_TO_DEVICE, 0);
> +               if (virtqueue_dma_mapping_error(sq->vq, addr))
> +                       goto err;
> +
> +               sg->dma_address = addr;
> +
> +               tail = p;
> +               tail->addr = sg->dma_address;
> +               tail->len = sg->length;
> +
> +               p = p->next;
> +       }
> +
> +       return virtnet_sq_dma_splice(sq, head, tail, data);
> +
> +err:
> +       if (tail)
> +               virtnet_sq_unmap(sq, virtnet_sq_dma_splice(sq, head, tail, data));
> +
> +       return NULL;
> +}
> +
> +static int virtnet_add_outbuf(struct send_queue *sq, u32 num, void *data)
> +{
> +       int ret;
> +
> +       if (sq->vq->premapped) {
> +               data = virtnet_sq_map_sg(sq, num, data);
> +               if (!data)
> +                       return -ENOMEM;
> +       }
> +
> +       ret = virtqueue_add_outbuf(sq->vq, sq->sg, num, data, GFP_ATOMIC);
> +       if (ret && sq->vq->premapped)
> +               virtnet_sq_unmap(sq, data);
> +
> +       return ret;
> +}
> +
> +static int virtnet_sq_init_dma_mate(struct send_queue *sq)
> +{
> +       struct virtnet_sq_dma *d;
> +       int size, i;
> +
> +       size = virtqueue_get_vring_size(sq->vq);
> +
> +       size += MAX_SKB_FRAGS + 2;

Is this enough for the case where an indirect descriptor is used?

Thanks