Date: Thu, 25 Jan 2024 18:17:40 +0800
From: Liang Chen <liangchen.linux@...il.com>
To: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Cc: virtualization@...ts.linux-foundation.org, linux-kernel@...r.kernel.org, 
	mst@...hat.com, jasowang@...hat.com, hengqi@...ux.alibaba.com
Subject: Re: [PATCH v2 1/3] virtio_net: Preserve virtio header before XDP
 program execution

On Wed, Jan 24, 2024 at 5:08 PM Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
>
> On Wed, 24 Jan 2024 16:57:19 +0800, Liang Chen <liangchen.linux@...il.com> wrote:
> > The xdp program may overwrite the inline virtio header. To ensure the
> > integrity of the virtio header, it is saved in a data structure that
> > wraps both the xdp_buff and the header before running the xdp program.
> >
> > Signed-off-by: Liang Chen <liangchen.linux@...il.com>
> > ---
> >  drivers/net/virtio_net.c | 43 +++++++++++++++++++++++++++++-----------
> >  1 file changed, 31 insertions(+), 12 deletions(-)
> >
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index d7ce4a1011ea..b56828804e5f 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -349,6 +349,11 @@ struct virtio_net_common_hdr {
> >       };
> >  };
> >
> > +struct virtnet_xdp_buff {
> > +     struct xdp_buff xdp;
> > +     struct virtio_net_common_hdr hdr;
>
> Not all items of the hdr are useful, we can just save the useful items.
>

Sure. Will do in v3. Thanks.

> > +};
> > +
> >  static void virtnet_sq_free_unused_buf(struct virtqueue *vq, void *buf);
> >
> >  static bool is_xdp_frame(void *ptr)
> > @@ -1199,9 +1204,10 @@ static struct sk_buff *receive_small_xdp(struct net_device *dev,
> >       unsigned int headroom = vi->hdr_len + header_offset;
> >       struct virtio_net_hdr_mrg_rxbuf *hdr = buf + header_offset;
> >       struct page *page = virt_to_head_page(buf);
> > +     struct virtnet_xdp_buff virtnet_xdp;
> >       struct page *xdp_page;
> > +     struct xdp_buff *xdp;
> >       unsigned int buflen;
> > -     struct xdp_buff xdp;
> >       struct sk_buff *skb;
> >       unsigned int metasize = 0;
> >       u32 act;
> > @@ -1233,17 +1239,23 @@ static struct sk_buff *receive_small_xdp(struct net_device *dev,
> >               page = xdp_page;
> >       }
> >
> > -     xdp_init_buff(&xdp, buflen, &rq->xdp_rxq);
> > -     xdp_prepare_buff(&xdp, buf + VIRTNET_RX_PAD + vi->hdr_len,
> > +     xdp = &virtnet_xdp.xdp;
> > +     xdp_init_buff(xdp, buflen, &rq->xdp_rxq);
> > +     xdp_prepare_buff(xdp, buf + VIRTNET_RX_PAD + vi->hdr_len,
> >                        xdp_headroom, len, true);
> >
> > -     act = virtnet_xdp_handler(xdp_prog, &xdp, dev, xdp_xmit, stats);
> > +     /* Copy out the virtio header, as it may be overwritten by the
> > +      * xdp program.
> > +      */
> > +     memcpy(&virtnet_xdp.hdr, hdr, vi->hdr_len);
>
> Can we put this into virtnet_xdp_handler?
>
> And just do that when the hash is negotiated.
>
> > +
> > +     act = virtnet_xdp_handler(xdp_prog, xdp, dev, xdp_xmit, stats);
> >
> >       switch (act) {
> >       case XDP_PASS:
> >               /* Recalculate length in case bpf program changed it */
> > -             len = xdp.data_end - xdp.data;
> > -             metasize = xdp.data - xdp.data_meta;
> > +             len = xdp->data_end - xdp->data;
> > +             metasize = xdp->data - xdp->data_meta;
> >               break;
> >
> >       case XDP_TX:
> > @@ -1254,7 +1266,7 @@ static struct sk_buff *receive_small_xdp(struct net_device *dev,
> >               goto err_xdp;
> >       }
> >
> > -     skb = virtnet_build_skb(buf, buflen, xdp.data - buf, len);
> > +     skb = virtnet_build_skb(buf, buflen, xdp->data - buf, len);
> >       if (unlikely(!skb))
> >               goto err;
> >
> > @@ -1591,10 +1603,11 @@ static struct sk_buff *receive_mergeable_xdp(struct net_device *dev,
> >       int num_buf = virtio16_to_cpu(vi->vdev, hdr->num_buffers);
> >       struct page *page = virt_to_head_page(buf);
> >       int offset = buf - page_address(page);
> > +     struct virtnet_xdp_buff virtnet_xdp;
> >       unsigned int xdp_frags_truesz = 0;
> >       struct sk_buff *head_skb;
> >       unsigned int frame_sz;
> > -     struct xdp_buff xdp;
> > +     struct xdp_buff *xdp;
> >       void *data;
> >       u32 act;
> >       int err;
> > @@ -1604,16 +1617,22 @@ static struct sk_buff *receive_mergeable_xdp(struct net_device *dev,
> >       if (unlikely(!data))
> >               goto err_xdp;
> >
> > -     err = virtnet_build_xdp_buff_mrg(dev, vi, rq, &xdp, data, len, frame_sz,
> > +     xdp = &virtnet_xdp.xdp;
> > +     err = virtnet_build_xdp_buff_mrg(dev, vi, rq, xdp, data, len, frame_sz,
> >                                        &num_buf, &xdp_frags_truesz, stats);
> >       if (unlikely(err))
> >               goto err_xdp;
> >
> > -     act = virtnet_xdp_handler(xdp_prog, &xdp, dev, xdp_xmit, stats);
> > +     /* Copy out the virtio header, as it may be overwritten by the
> > +      * xdp program.
> > +      */
> > +     memcpy(&virtnet_xdp.hdr, hdr, vi->hdr_len);
> > +
> > +     act = virtnet_xdp_handler(xdp_prog, xdp, dev, xdp_xmit, stats);
> >
> >       switch (act) {
> >       case XDP_PASS:
> > -             head_skb = build_skb_from_xdp_buff(dev, vi, &xdp, xdp_frags_truesz);
> > +             head_skb = build_skb_from_xdp_buff(dev, vi, xdp, xdp_frags_truesz);
> >               if (unlikely(!head_skb))
> >                       break;
> >               return head_skb;
> > @@ -1626,7 +1645,7 @@ static struct sk_buff *receive_mergeable_xdp(struct net_device *dev,
> >               break;
> >       }
> >
> > -     put_xdp_frags(&xdp);
> > +     put_xdp_frags(xdp);
> >
> >  err_xdp:
> >       put_page(page);
> > --
> > 2.40.1
> >

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