On Mon, Jun 17, 2024 at 9:15 PM Heng Qi <hengqi@xxxxxxxxxxxxxxxxx> wrote:
>
> The XDP program can't correctly handle partially checksummed
> packets, but works fine with fully checksummed packets.
Not sure this is ture, if I was not wrong, XDP can try to calculate checksum.
Thanks
> If the
> device has already validated fully checksummed packets, then
> the driver doesn't need to re-validate them, saving CPU resources.
>
> Additionally, the driver does not drop all partially checksummed
> packets when VIRTIO_NET_F_GUEST_CSUM is not negotiated. This is
> not a bug, as the driver has always done this.
>
> Fixes: 436c9453a1ac ("virtio-net: keep vnet header zeroed after processing XDP")
> Signed-off-by: Heng Qi <hengqi@xxxxxxxxxxxxxxxxx>
> ---
> drivers/net/virtio_net.c | 20 +++++++++++++++++++-
> 1 file changed, 19 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index aa70a7ed8072..ea10db9a09fa 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1360,6 +1360,10 @@ static struct sk_buff *receive_small_xdp(struct net_device *dev,
> if (unlikely(hdr->hdr.gso_type))
> goto err_xdp;
>
> + /* Partially checksummed packets must be dropped. */
> + if (unlikely(hdr->hdr.flags & VIRTIO_NET_HDR_F_NEEDS_CSUM))
> + goto err_xdp;
> +
> buflen = SKB_DATA_ALIGN(GOOD_PACKET_LEN + headroom) +
> SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
>
> @@ -1677,6 +1681,10 @@ static void *mergeable_xdp_get_buf(struct virtnet_info *vi,
> if (unlikely(hdr->hdr.gso_type))
> return NULL;
>
> + /* Partially checksummed packets must be dropped. */
> + if (unlikely(hdr->hdr.flags & VIRTIO_NET_HDR_F_NEEDS_CSUM))
> + return NULL;
> +
> /* Now XDP core assumes frag size is PAGE_SIZE, but buffers
> * with headroom may add hole in truesize, which
> * make their length exceed PAGE_SIZE. So we disabled the
> @@ -1943,6 +1951,7 @@ static void receive_buf(struct virtnet_info *vi, struct receive_queue *rq,
> struct net_device *dev = vi->dev;
> struct sk_buff *skb;
> struct virtio_net_common_hdr *hdr;
> + u8 flags;
>
> if (unlikely(len < vi->hdr_len + ETH_HLEN)) {
> pr_debug("%s: short packet %i\n", dev->name, len);
> @@ -1951,6 +1960,15 @@ static void receive_buf(struct virtnet_info *vi, struct receive_queue *rq,
> return;
> }
>
> + /* 1. Save the flags early, as the XDP program might overwrite them.
> + * These flags ensure packets marked as VIRTIO_NET_HDR_F_DATA_VALID
> + * stay valid after XDP processing.
> + * 2. XDP doesn't work with partially checksummed packets (refer to
> + * virtnet_xdp_set()), so packets marked as
> + * VIRTIO_NET_HDR_F_NEEDS_CSUM get dropped during XDP processing.
> + */
> + flags = ((struct virtio_net_common_hdr *)buf)->hdr.flags;
> +
> if (vi->mergeable_rx_bufs)
> skb = receive_mergeable(dev, vi, rq, buf, ctx, len, xdp_xmit,
> stats);
> @@ -1966,7 +1984,7 @@ static void receive_buf(struct virtnet_info *vi, struct receive_queue *rq,
> if (dev->features & NETIF_F_RXHASH && vi->has_rss_hash_report)
> virtio_skb_set_hash(&hdr->hash_v1_hdr, skb);
>
> - if (hdr->hdr.flags & VIRTIO_NET_HDR_F_DATA_VALID)
> + if (flags & VIRTIO_NET_HDR_F_DATA_VALID)
> skb->ip_summed = CHECKSUM_UNNECESSARY;
>
> if (virtio_net_hdr_to_skb(skb, &hdr->hdr,
> --
> 2.32.0.3.g01195cf9f
>
