Re: [PATCH net-next 3/8] virtio_net: introduce virtnet_xdp_handler() to seprate the logic of run xdp

[Jason Wang <jasowang@redhat.com>]

On Mon, Apr 3, 2023 at 12:17 PM Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote:
>
> On Mon, 3 Apr 2023 10:43:03 +0800, Jason Wang <jasowang@redhat.com> wrote:
> > On Tue, Mar 28, 2023 at 8:04 PM Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote:
> > >
> > > At present, we have two similar logic to perform the XDP prog.
> > >
> > > Therefore, this PATCH separates the code of executing XDP, which is
> > > conducive to later maintenance.
> > >
> > > Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> > > ---
> > >  drivers/net/virtio_net.c | 142 +++++++++++++++++++++------------------
> > >  1 file changed, 75 insertions(+), 67 deletions(-)
> > >
> > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > > index bb426958cdd4..72b9d6ee4024 100644
> > > --- a/drivers/net/virtio_net.c
> > > +++ b/drivers/net/virtio_net.c
> > > @@ -301,6 +301,15 @@ struct padded_vnet_hdr {
> > >         char padding[12];
> > >  };
> > >
> > > +enum {
> > > +       /* xdp pass */
> > > +       VIRTNET_XDP_RES_PASS,
> > > +       /* drop packet. the caller needs to release the page. */
> > > +       VIRTNET_XDP_RES_DROP,
> > > +       /* packet is consumed by xdp. the caller needs to do nothing. */
> > > +       VIRTNET_XDP_RES_CONSUMED,
> > > +};
> >
> > I'd prefer this to be done on top unless it is a must. But I don't see
> > any advantage of introducing this, it's partial mapping of XDP action
> > and it needs to be extended when XDP action is extended. (And we've
> > already had: VIRTIO_XDP_REDIR and VIRTIO_XDP_TX ...)
>
> No, these are the three states of buffer after XDP processing.
>
> * PASS: goto make skb

XDP_PASS goes for this.

> * DROP: we should release buffer

XDP_DROP and error conditions go with this.

> * CUNSUMED: xdp prog used the buffer, we do nothing

XDP_TX/XDP_REDIRECTION goes for this.

So t virtnet_xdp_handler() just maps XDP ACTION plus the error
conditions to the above three states.

We can simply map error to XDP_DROP like:

       case XDP_TX:
              stats->xdp_tx++;
               xdpf = xdp_convert_buff_to_frame(xdp);
               if (unlikely(!xdpf))
                       return XDP_DROP;

A good side effect is to avoid the xdp_xmit pointer to be passed to
the function.

>
> The latter two are not particularly related to XDP ACTION. And it does not need
> to extend when XDP action is extended. At least I have not thought of this
> situation.

What's the advantages of such indirection compared to using XDP action directly?

Thanks

>
>
> >
> > > +
> > >  static void virtnet_rq_free_unused_buf(struct virtqueue *vq, void *buf);
> > >  static void virtnet_sq_free_unused_buf(struct virtqueue *vq, void *buf);
> > >
> > > @@ -789,6 +798,59 @@ static int virtnet_xdp_xmit(struct net_device *dev,
> > >         return ret;
> > >  }
> > >
> > > +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)
> > > +{
> > > +       struct xdp_frame *xdpf;
> > > +       int err;
> > > +       u32 act;
> > > +
> > > +       act = bpf_prog_run_xdp(xdp_prog, xdp);
> > > +       stats->xdp_packets++;
> > > +
> > > +       switch (act) {
> > > +       case XDP_PASS:
> > > +               return VIRTNET_XDP_RES_PASS;
> > > +
> > > +       case XDP_TX:
> > > +               stats->xdp_tx++;
> > > +               xdpf = xdp_convert_buff_to_frame(xdp);
> > > +               if (unlikely(!xdpf))
> > > +                       return VIRTNET_XDP_RES_DROP;
> > > +
> > > +               err = virtnet_xdp_xmit(dev, 1, &xdpf, 0);
> > > +               if (unlikely(!err)) {
> > > +                       xdp_return_frame_rx_napi(xdpf);
> > > +               } else if (unlikely(err < 0)) {
> > > +                       trace_xdp_exception(dev, xdp_prog, act);
> > > +                       return VIRTNET_XDP_RES_DROP;
> > > +               }
> > > +
> > > +               *xdp_xmit |= VIRTIO_XDP_TX;
> > > +               return VIRTNET_XDP_RES_CONSUMED;
> > > +
> > > +       case XDP_REDIRECT:
> > > +               stats->xdp_redirects++;
> > > +               err = xdp_do_redirect(dev, xdp, xdp_prog);
> > > +               if (err)
> > > +                       return VIRTNET_XDP_RES_DROP;
> > > +
> > > +               *xdp_xmit |= VIRTIO_XDP_REDIR;
> > > +               return VIRTNET_XDP_RES_CONSUMED;
> > > +
> > > +       default:
> > > +               bpf_warn_invalid_xdp_action(dev, xdp_prog, act);
> > > +               fallthrough;
> > > +       case XDP_ABORTED:
> > > +               trace_xdp_exception(dev, xdp_prog, act);
> > > +               fallthrough;
> > > +       case XDP_DROP:
> > > +               return VIRTNET_XDP_RES_DROP;
> > > +       }
> > > +}
> > > +
> > >  static unsigned int virtnet_get_headroom(struct virtnet_info *vi)
> > >  {
> > >         return vi->xdp_enabled ? VIRTIO_XDP_HEADROOM : 0;
> > > @@ -876,7 +938,6 @@ static struct sk_buff *receive_small(struct net_device *dev,
> > >         struct page *page = virt_to_head_page(buf);
> > >         unsigned int delta = 0;
> > >         struct page *xdp_page;
> > > -       int err;
> > >         unsigned int metasize = 0;
> > >
> > >         len -= vi->hdr_len;
> > > @@ -898,7 +959,6 @@ static struct sk_buff *receive_small(struct net_device *dev,
> > >         xdp_prog = rcu_dereference(rq->xdp_prog);
> > >         if (xdp_prog) {
> > >                 struct virtio_net_hdr_mrg_rxbuf *hdr = buf + header_offset;
> > > -               struct xdp_frame *xdpf;
> > >                 struct xdp_buff xdp;
> > >                 void *orig_data;
> > >                 u32 act;
> > > @@ -931,46 +991,22 @@ static struct sk_buff *receive_small(struct net_device *dev,
> > >                 xdp_prepare_buff(&xdp, buf + VIRTNET_RX_PAD + vi->hdr_len,
> > >                                  xdp_headroom, len, true);
> > >                 orig_data = xdp.data;
> > > -               act = bpf_prog_run_xdp(xdp_prog, &xdp);
> > > -               stats->xdp_packets++;
> > > +
> > > +               act = virtnet_xdp_handler(xdp_prog, &xdp, dev, xdp_xmit, stats);
> > >
> > >                 switch (act) {
> > > -               case XDP_PASS:
> > > +               case VIRTNET_XDP_RES_PASS:
> > >                         /* Recalculate length in case bpf program changed it */
> > >                         delta = orig_data - xdp.data;
> > >                         len = xdp.data_end - xdp.data;
> > >                         metasize = xdp.data - xdp.data_meta;
> > >                         break;
> > > -               case XDP_TX:
> > > -                       stats->xdp_tx++;
> > > -                       xdpf = xdp_convert_buff_to_frame(&xdp);
> > > -                       if (unlikely(!xdpf))
> > > -                               goto err_xdp;
> > > -                       err = virtnet_xdp_xmit(dev, 1, &xdpf, 0);
> > > -                       if (unlikely(!err)) {
> > > -                               xdp_return_frame_rx_napi(xdpf);
> > > -                       } else if (unlikely(err < 0)) {
> > > -                               trace_xdp_exception(vi->dev, xdp_prog, act);
> > > -                               goto err_xdp;
> > > -                       }
> > > -                       *xdp_xmit |= VIRTIO_XDP_TX;
> > > -                       rcu_read_unlock();
> > > -                       goto xdp_xmit;
> > > -               case XDP_REDIRECT:
> > > -                       stats->xdp_redirects++;
> > > -                       err = xdp_do_redirect(dev, &xdp, xdp_prog);
> > > -                       if (err)
> > > -                               goto err_xdp;
> > > -                       *xdp_xmit |= VIRTIO_XDP_REDIR;
> > > +
> > > +               case VIRTNET_XDP_RES_CONSUMED:
> > >                         rcu_read_unlock();
> > >                         goto xdp_xmit;
> > > -               default:
> > > -                       bpf_warn_invalid_xdp_action(vi->dev, xdp_prog, act);
> > > -                       fallthrough;
> > > -               case XDP_ABORTED:
> > > -                       trace_xdp_exception(vi->dev, xdp_prog, act);
> > > -                       goto err_xdp;
> > > -               case XDP_DROP:
> > > +
> > > +               case VIRTNET_XDP_RES_DROP:
> > >                         goto err_xdp;
> > >                 }
> > >         }
> > > @@ -1277,7 +1313,6 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
> > >         if (xdp_prog) {
> > >                 unsigned int xdp_frags_truesz = 0;
> > >                 struct skb_shared_info *shinfo;
> > > -               struct xdp_frame *xdpf;
> > >                 struct page *xdp_page;
> > >                 struct xdp_buff xdp;
> > >                 void *data;
> > > @@ -1294,49 +1329,22 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
> > >                 if (unlikely(err))
> > >                         goto err_xdp_frags;
> > >
> > > -               act = bpf_prog_run_xdp(xdp_prog, &xdp);
> > > -               stats->xdp_packets++;
> > > +               act = virtnet_xdp_handler(xdp_prog, &xdp, dev, xdp_xmit, stats);
> > >
> > >                 switch (act) {
> > > -               case XDP_PASS:
> > > +               case VIRTNET_XDP_RES_PASS:
> > >                         head_skb = build_skb_from_xdp_buff(dev, vi, &xdp, xdp_frags_truesz);
> > >                         if (unlikely(!head_skb))
> > >                                 goto err_xdp_frags;
> > >
> > >                         rcu_read_unlock();
> > >                         return head_skb;
> > > -               case XDP_TX:
> > > -                       stats->xdp_tx++;
> > > -                       xdpf = xdp_convert_buff_to_frame(&xdp);
> > > -                       if (unlikely(!xdpf)) {
> > > -                               netdev_dbg(dev, "convert buff to frame failed for xdp\n");
> >
> > Nit: This debug is lost after the conversion.
>
> Will fix.
>
> Thanks.
>
> >
> > Thanks
> >
> > > -                               goto err_xdp_frags;
> > > -                       }
> > > -                       err = virtnet_xdp_xmit(dev, 1, &xdpf, 0);
> > > -                       if (unlikely(!err)) {
> > > -                               xdp_return_frame_rx_napi(xdpf);
> > > -                       } else if (unlikely(err < 0)) {
> > > -                               trace_xdp_exception(vi->dev, xdp_prog, act);
> > > -                               goto err_xdp_frags;
> > > -                       }
> > > -                       *xdp_xmit |= VIRTIO_XDP_TX;
> > > -                       rcu_read_unlock();
> > > -                       goto xdp_xmit;
> > > -               case XDP_REDIRECT:
> > > -                       stats->xdp_redirects++;
> > > -                       err = xdp_do_redirect(dev, &xdp, xdp_prog);
> > > -                       if (err)
> > > -                               goto err_xdp_frags;
> > > -                       *xdp_xmit |= VIRTIO_XDP_REDIR;
> > > +
> > > +               case VIRTNET_XDP_RES_CONSUMED:
> > >                         rcu_read_unlock();
> > >                         goto xdp_xmit;
> > > -               default:
> > > -                       bpf_warn_invalid_xdp_action(vi->dev, xdp_prog, act);
> > > -                       fallthrough;
> > > -               case XDP_ABORTED:
> > > -                       trace_xdp_exception(vi->dev, xdp_prog, act);
> > > -                       fallthrough;
> > > -               case XDP_DROP:
> > > +
> > > +               case VIRTNET_XDP_RES_DROP:
> > >                         goto err_xdp_frags;
> > >                 }
> > >  err_xdp_frags:
> > > --
> > > 2.32.0.3.g01195cf9f
> > >
> >
>