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Date: Wed, 28 Jun 2023 11:22:48 +0800
From: Jason Wang <jasowang@...hat.com>
To: Heng Qi <hengqi@...ux.alibaba.com>
Cc: netdev@...r.kernel.org, bpf@...r.kernel.org,
"Michael S . Tsirkin" <mst@...hat.com>, "David S . Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>, Jesper Dangaard Brouer <hawk@...nel.org>,
John Fastabend <john.fastabend@...il.com>, Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Subject: Re: [PATCH net-next v4 1/2] virtio-net: support coexistence of XDP
and GUEST_CSUM
On Wed, Jun 28, 2023 at 11:05 AM Heng Qi <hengqi@...ux.alibaba.com> wrote:
>
> We are now re-probing the csum related fields and trying
> to have XDP and RX hw checksum capabilities coexist on the
> XDP path. For the benefit of:
> 1. RX hw checksum capability can be used if XDP is loaded.
> 2. Avoid packet loss when loading XDP in the vm-vm scenario.
>
> Signed-off-by: Heng Qi <hengqi@...ux.alibaba.com>
> Reviewed-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> ---
> v3->v4:
> - Rewrite some comments.
>
> v2->v3:
> - Use skb_checksum_setup() instead of virtnet_flow_dissect_udp_tcp().
> Essentially equivalent.
>
> drivers/net/virtio_net.c | 82 +++++++++++++++++++++++++++++++++-------
> 1 file changed, 69 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 5a7f7a76b920..a47342f972b5 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1568,6 +1568,41 @@ static void virtio_skb_set_hash(const struct virtio_net_hdr_v1_hash *hdr_hash,
> skb_set_hash(skb, __le32_to_cpu(hdr_hash->hash_value), rss_hash_type);
> }
>
> +static int virtnet_set_csum_after_xdp(struct virtnet_info *vi,
> + struct sk_buff *skb,
> + __u8 flags)
> +{
> + int err = 0;
> +
> + /* When XDP program is loaded, the vm-vm scenario on the same host,
> + * packets marked VIRTIO_NET_HDR_F_NEEDS_CSUM without a complete checksum
> + * will travel. Although these packets are safe from the point of
> + * view of the vm, in order to be successfully forwarded on the upper
> + * layer and to avoid packet loss caused by XDP modification,
> + * we re-probe the necessary checksum related information:
> + * skb->csum_{start, offset}, pseudo-header checksum.
> + *
> + * If the received packet is marked VIRTIO_NET_HDR_F_DATA_VALID:
> + * when _F_GUEST_CSUM is negotiated, the device validates the checksum
> + * and virtio-net sets skb->ip_summed to CHECKSUM_UNNECESSARY;
> + * otherwise, virtio-net hands over to the stack to validate the checksum.
> + */
> + if (flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) {
> + /* No need to care about SCTP because virtio-net currently doesn't
> + * support SCTP CRC checksum offloading, that is, SCTP packets have
> + * complete checksums.
> + */
> + err = skb_checksum_setup(skb, true);
A second thought, any reason why a checksum is a must here. Could we simply:
1) probe the csum_start/offset
2) leave it as CHECKSUM_PARTIAL
?
> + } else if (flags & VIRTIO_NET_HDR_F_DATA_VALID) {
> + /* XDP guarantees that packets marked as VIRTIO_NET_HDR_F_DATA_VALID
> + * still have correct checksum after they are processed.
> + */
Do you mean it's the charge of the XDP program to calculate the csum
in this case? Seems strange.
Thanks
> + skb->ip_summed = CHECKSUM_UNNECESSARY;
> + }
> +
> + return err;
> +}
> +
> static void receive_buf(struct virtnet_info *vi, struct receive_queue *rq,
> void *buf, unsigned int len, void **ctx,
> unsigned int *xdp_xmit,
> @@ -1576,6 +1611,7 @@ 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_hdr_mrg_rxbuf *hdr;
> + __u8 flags;
>
> if (unlikely(len < vi->hdr_len + ETH_HLEN)) {
> pr_debug("%s: short packet %i\n", dev->name, len);
> @@ -1584,6 +1620,12 @@ static void receive_buf(struct virtnet_info *vi, struct receive_queue *rq,
> return;
> }
>
> + /* XDP may modify/overwrite the packet, including the virtnet hdr,
> + * so save the flags of the virtnet hdr before XDP processing.
> + */
> + if (unlikely(vi->xdp_enabled))
> + flags = ((struct virtio_net_hdr_mrg_rxbuf *)buf)->hdr.flags;
> +
> if (vi->mergeable_rx_bufs)
> skb = receive_mergeable(dev, vi, rq, buf, ctx, len, xdp_xmit,
> stats);
> @@ -1595,23 +1637,37 @@ static void receive_buf(struct virtnet_info *vi, struct receive_queue *rq,
> if (unlikely(!skb))
> return;
>
> - hdr = skb_vnet_hdr(skb);
> - if (dev->features & NETIF_F_RXHASH && vi->has_rss_hash_report)
> - virtio_skb_set_hash((const struct virtio_net_hdr_v1_hash *)hdr, skb);
> -
> - if (hdr->hdr.flags & VIRTIO_NET_HDR_F_DATA_VALID)
> - skb->ip_summed = CHECKSUM_UNNECESSARY;
> + if (unlikely(vi->xdp_enabled)) {
> + /* Required to do this before re-probing and calculating
> + * the pseudo-header checksum.
> + */
> + skb->protocol = eth_type_trans(skb, dev);
> + skb_reset_network_header(skb);
> + if (virtnet_set_csum_after_xdp(vi, skb, flags) < 0) {
> + pr_debug("%s: errors occurred in setting partial csum",
> + dev->name);
> + goto frame_err;
> + }
> + } else {
> + hdr = skb_vnet_hdr(skb);
> + if (dev->features & NETIF_F_RXHASH && vi->has_rss_hash_report)
> + virtio_skb_set_hash((const struct virtio_net_hdr_v1_hash *)hdr, skb);
> +
> + if (hdr->hdr.flags & VIRTIO_NET_HDR_F_DATA_VALID)
> + skb->ip_summed = CHECKSUM_UNNECESSARY;
> +
> + if (virtio_net_hdr_to_skb(skb, &hdr->hdr,
> + virtio_is_little_endian(vi->vdev))) {
> + net_warn_ratelimited("%s: bad gso: type: %u, size: %u\n",
> + dev->name, hdr->hdr.gso_type,
> + hdr->hdr.gso_size);
> + goto frame_err;
> + }
>
> - if (virtio_net_hdr_to_skb(skb, &hdr->hdr,
> - virtio_is_little_endian(vi->vdev))) {
> - net_warn_ratelimited("%s: bad gso: type: %u, size: %u\n",
> - dev->name, hdr->hdr.gso_type,
> - hdr->hdr.gso_size);
> - goto frame_err;
> + skb->protocol = eth_type_trans(skb, dev);
> }
>
> skb_record_rx_queue(skb, vq2rxq(rq->vq));
> - skb->protocol = eth_type_trans(skb, dev);
> pr_debug("Receiving skb proto 0x%04x len %i type %i\n",
> ntohs(skb->protocol), skb->len, skb->pkt_type);
>
> --
> 2.19.1.6.gb485710b
>
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