Re: [PATCH net-next v7 09/10] virtio_net: xsk: rx: support recv small mode

[Jason Wang <jasowang@redhat.com>]

On Mon, Jul 8, 2024 at 3:47 PM Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote:
>
> On Mon, 8 Jul 2024 15:00:50 +0800, Jason Wang <jasowang@redhat.com> wrote:
> > On Fri, Jul 5, 2024 at 3:38 PM Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote:
> > >
> > > In the process:
> > > 1. We may need to copy data to create skb for XDP_PASS.
> > > 2. We may need to call xsk_buff_free() to release the buffer.
> > > 3. The handle for xdp_buff is difference from the buffer.
> > >
> > > If we pushed this logic into existing receive handle(merge and small),
> > > we would have to maintain code scattered inside merge and small (and big).
> > > So I think it is a good choice for us to put the xsk code into an
> > > independent function.
> > >
> > > Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> > > ---
> > >
> > > v7:
> > >    1. rename xdp_construct_skb to xsk_construct_skb
> > >    2. refactor virtnet_receive()
> > >
> > >  drivers/net/virtio_net.c | 176 +++++++++++++++++++++++++++++++++++++--
> > >  1 file changed, 168 insertions(+), 8 deletions(-)
> > >
> > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > > index 2b27f5ada64a..64d8cd481890 100644
> > > --- a/drivers/net/virtio_net.c
> > > +++ b/drivers/net/virtio_net.c
> > > @@ -498,6 +498,12 @@ struct virtio_net_common_hdr {
> > >  };
> > >
> > >  static void virtnet_sq_free_unused_buf(struct virtqueue *vq, void *buf);
> > > +static int virtnet_xdp_handler(struct bpf_prog *xdp_prog, struct xdp_buff *xdp,
> > > +                              struct net_device *dev,
> > > +                              unsigned int *xdp_xmit,
> > > +                              struct virtnet_rq_stats *stats);
> > > +static void virtnet_receive_done(struct virtnet_info *vi, struct receive_queue *rq,
> > > +                                struct sk_buff *skb, u8 flags);
> > >
> > >  static bool is_xdp_frame(void *ptr)
> > >  {
> > > @@ -1062,6 +1068,124 @@ static void sg_fill_dma(struct scatterlist *sg, dma_addr_t addr, u32 len)
> > >         sg->length = len;
> > >  }
> > >
> > > +static struct xdp_buff *buf_to_xdp(struct virtnet_info *vi,
> > > +                                  struct receive_queue *rq, void *buf, u32 len)
> > > +{
> > > +       struct xdp_buff *xdp;
> > > +       u32 bufsize;
> > > +
> > > +       xdp = (struct xdp_buff *)buf;
> > > +
> > > +       bufsize = xsk_pool_get_rx_frame_size(rq->xsk_pool) + vi->hdr_len;
> > > +
> > > +       if (unlikely(len > bufsize)) {
> > > +               pr_debug("%s: rx error: len %u exceeds truesize %u\n",
> > > +                        vi->dev->name, len, bufsize);
> > > +               DEV_STATS_INC(vi->dev, rx_length_errors);
> > > +               xsk_buff_free(xdp);
> > > +               return NULL;
> > > +       }
> > > +
> > > +       xsk_buff_set_size(xdp, len);
> > > +       xsk_buff_dma_sync_for_cpu(xdp);
> > > +
> > > +       return xdp;
> > > +}
> > > +
> > > +static struct sk_buff *xsk_construct_skb(struct receive_queue *rq,
> > > +                                        struct xdp_buff *xdp)
> > > +{
> > > +       unsigned int metasize = xdp->data - xdp->data_meta;
> > > +       struct sk_buff *skb;
> > > +       unsigned int size;
> > > +
> > > +       size = xdp->data_end - xdp->data_hard_start;
> > > +       skb = napi_alloc_skb(&rq->napi, size);
> > > +       if (unlikely(!skb)) {
> > > +               xsk_buff_free(xdp);
> > > +               return NULL;
> > > +       }
> > > +
> > > +       skb_reserve(skb, xdp->data_meta - xdp->data_hard_start);
> > > +
> > > +       size = xdp->data_end - xdp->data_meta;
> > > +       memcpy(__skb_put(skb, size), xdp->data_meta, size);
> > > +
> > > +       if (metasize) {
> > > +               __skb_pull(skb, metasize);
> > > +               skb_metadata_set(skb, metasize);
> > > +       }
> > > +
> > > +       xsk_buff_free(xdp);
> > > +
> > > +       return skb;
> > > +}
> > > +
> > > +static struct sk_buff *virtnet_receive_xsk_small(struct net_device *dev, struct virtnet_info *vi,
> > > +                                                struct receive_queue *rq, struct xdp_buff *xdp,
> > > +                                                unsigned int *xdp_xmit,
> > > +                                                struct virtnet_rq_stats *stats)
> > > +{
> > > +       struct bpf_prog *prog;
> > > +       u32 ret;
> > > +
> > > +       ret = XDP_PASS;
> > > +       rcu_read_lock();
> > > +       prog = rcu_dereference(rq->xdp_prog);
> > > +       if (prog)
> > > +               ret = virtnet_xdp_handler(prog, xdp, dev, xdp_xmit, stats);
> > > +       rcu_read_unlock();
> > > +
> > > +       switch (ret) {
> > > +       case XDP_PASS:
> > > +               return xsk_construct_skb(rq, xdp);
> > > +
> > > +       case XDP_TX:
> > > +       case XDP_REDIRECT:
> > > +               return NULL;
> > > +
> > > +       default:
> > > +               /* drop packet */
> > > +               xsk_buff_free(xdp);
> > > +               u64_stats_inc(&stats->drops);
> > > +               return NULL;
> > > +       }
> > > +}
> > > +
> > > +static void virtnet_receive_xsk_buf(struct virtnet_info *vi, struct receive_queue *rq,
> > > +                                   void *buf, u32 len,
> > > +                                   unsigned int *xdp_xmit,
> > > +                                   struct virtnet_rq_stats *stats)
> > > +{
> > > +       struct net_device *dev = vi->dev;
> > > +       struct sk_buff *skb = NULL;
> > > +       struct xdp_buff *xdp;
> > > +       u8 flags;
> > > +
> > > +       len -= vi->hdr_len;
> > > +
> > > +       u64_stats_add(&stats->bytes, len);
> > > +
> > > +       xdp = buf_to_xdp(vi, rq, buf, len);
> > > +       if (!xdp)
> > > +               return;
> > > +
> > > +       if (unlikely(len < ETH_HLEN)) {
> > > +               pr_debug("%s: short packet %i\n", dev->name, len);
> > > +               DEV_STATS_INC(dev, rx_length_errors);
> > > +               xsk_buff_free(xdp);
> > > +               return;
> > > +       }
> > > +
> > > +       flags = ((struct virtio_net_common_hdr *)(xdp->data - vi->hdr_len))->hdr.flags;
> > > +
> > > +       if (!vi->mergeable_rx_bufs)
> > > +               skb = virtnet_receive_xsk_small(dev, vi, rq, xdp, xdp_xmit, stats);
> >
> > I wonder if we add the mergeable support in the next patch would it be
> > better to re-order the patch? For example, the xsk binding needs to be
> > moved to the last patch, otherwise we break xsk with a mergeable
> > buffer here?
>
> If you worry that the user works with this commit, I want to say you do not
> worry.
>
> Because the flags NETDEV_XDP_ACT_XSK_ZEROCOPY is not added. I plan to add that
> after the tx is completed.

Ok, this is something I missed, it would be better to mention it
somewhere (or it is already there but I miss it).

>
> I do test by adding this flags locally.
>
> Thanks.

Acked-by: Jason Wang <jasowang@redhat.com>

Thanks

>
> >
> > Or anything I missed here?
> >
> > Thanks
> >
>