On Mon, Jun 19, 2023 at 06:57:36PM +0800, Heng Qi wrote:
> Currently, the VIRTIO_NET_F_GUEST_CSUM (corresponds to NETIF_F_RXCSUM
> for netdev) feature of the virtio-net driver conflicts with the loading
> of XDP, which is caused by the problem described in [1][2], that is,
> XDP may cause errors in partial csumed-related fields which can lead
> to packet dropping.
>
> In addition, when communicating between vm and vm on the same host, the
> receiving side vm will receive packets marked as
> VIRTIO_NET_HDR_F_NEEDS_CSUM, but after these packets are processed by
> XDP, the VIRTIO_NET_HDR_F_NEEDS_CSUM and skb CHECKSUM_PARTIAL flags will
> be cleared, causing the packet dropping.
>
> This patch introduces a helper function, which will try to solve the
> above problems in the subsequent patch.
>
> [1] commit 18ba58e1c234 ("virtio-net: fail XDP set if guest csum is negotiated")
> [2] commit e59ff2c49ae1 ("virtio-net: disable guest csum during XDP set")
>
> Signed-off-by: Heng Qi <hengqi@xxxxxxxxxxxxxxxxx>
> Reviewed-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
squash this and patch 1 into where the helpers are used.
in particular so we don't get warnings with bisect.
> ---
> drivers/net/virtio_net.c | 38 ++++++++++++++++++++++++++++++++++++++
> 1 file changed, 38 insertions(+)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 36cae78f6311..07b4801d689c 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1663,6 +1663,44 @@ static int virtnet_flow_dissect_udp_tcp(struct virtnet_info *vi, struct sk_buff
> return 0;
> }
>
> +static int virtnet_set_csum_after_xdp(struct virtnet_info *vi,
> + struct sk_buff *skb,
> + __u8 flags)
> +{
> + int err;
> +
> + /* When XDP program is loaded, for example, the vm-vm scenario
> + * on the same host, packets marked as VIRTIO_NET_HDR_F_NEEDS_CSUM
> + * will travel. Although these packets are safe from the point of
> + * view of the vm, to avoid modification by XDP and successful
> + * forwarding in the upper layer, we re-probe the necessary checksum
> + * related information: skb->csum_{start, offset}, pseudo-header csum.
> + *
> + * This benefits us:
> + * 1. XDP can be loaded when there's _F_GUEST_CSUM.
> + * 2. The device verifies the checksum of packets , especially
> + * benefiting for large packets.
> + * 3. In the same-host vm-vm scenario, packets marked as
> + * VIRTIO_NET_HDR_F_NEEDS_CSUM are no longer dropped after being
> + * processed by XDP.
> + */
> + if (flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) {
> + err = virtnet_flow_dissect_udp_tcp(vi, skb);
> + if (err < 0)
> + return -EINVAL;
> +
> + skb->ip_summed = CHECKSUM_PARTIAL;
> + } else if (flags && VIRTIO_NET_HDR_F_DATA_VALID) {
> + /* We want to benefit from this: XDP guarantees that packets marked
> + * as VIRTIO_NET_HDR_F_DATA_VALID still have correct csum after they
> + * are processed.
> + */
> + skb->ip_summed = CHECKSUM_UNNECESSARY;
> + }
> +
> + return 0;
> +}
> +
> static void receive_buf(struct virtnet_info *vi, struct receive_queue *rq,
> void *buf, unsigned int len, void **ctx,
> unsigned int *xdp_xmit,
> --
> 2.19.1.6.gb485710b
