On Mon, Jun 26, 2023 at 08:03:00PM +0800, Heng Qi 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@xxxxxxxxxxxxxxxxx>
> Reviewed-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
> ---
> v2->v3:
> - Use skb_checksum_setup() instead of virtnet_flow_dissect_udp_tcp().
> Essentially equivalent.
>
> drivers/net/virtio_net.c | 86 ++++++++++++++++++++++++++++++++++------
> 1 file changed, 73 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 5a7f7a76b920..0a715e0fbc97 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1568,6 +1568,44 @@ 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, 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,
why do you want tp avoid forwarding? did you mean
"and to allow forwarding"?
> we re-probe the necessary checksum
> + * related information: skb->csum_{start, offset}, pseudo-header csum
> + * using skb_chdcksum_setup().
typo
> + *
> + * This benefits us:
Drop "This benefits us:" - benefits compared to what?
> + * 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.
please rewrite so the text makes sense in the final C file,
not for someone reading the diff. In that cotext it does not
matter that we used to drop packets or that we used to
disable _F_GUEST_CSUM unless you explain
why they had to be dropped previously.
> + */
> + if (flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) {
> + /* We don't parse SCTP because virtio-net currently doesn't
> + * support CRC checksum offloading for SCTP.
what does this refer to? where does it exclude SCTP?
> + */
> + err = skb_checksum_setup(skb, true);
> + } 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.
drop "We want to benefit from this: "
> + */
> + 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 +1614,7 @@ 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 +1623,13 @@ static void receive_buf(struct virtnet_info *vi, struct receive_queue *rq,
> return;
> }
>
> + /* Save the flags of the hdr before XDP processes the data.
> + * It is ok to use this for both mergeable and small modes.
> + * Because that's what we do now.
What does the last sentence mean?
Instead please explain why this is necessary. what can change the
header?
> + */
> + 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 +1641,37 @@ 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.
What if checksum was disabled on device? No need for all the
elaborate hacks then, right?
What about disabling by ethtool?
> + */
> + 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
