Re: [PATCH net-next 3/4] virtio-net: support coexistence of XDP and _F_GUEST_CSUM

From: "Michael S. Tsirkin" <mst@redhat.com>
To: Heng Qi <hengqi@linux.alibaba.com>
Cc: netdev@vger.kernel.org, bpf@vger.kernel.org,
	Jason Wang <jasowang@redhat.com>,
	Xuan Zhuo <xuanzhuo@linux.alibaba.com>,
	"David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Jesper Dangaard Brouer <hawk@kernel.org>,
	John Fastabend <john.fastabend@gmail.com>
Subject: Re: [PATCH net-next 3/4] virtio-net: support coexistence of XDP and _F_GUEST_CSUM
Date: Mon, 19 Jun 2023 07:26:44 -0400	[thread overview]
Message-ID: <20230619072320-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <20230619105738.117733-4-hengqi@linux.alibaba.com>

On Mon, Jun 19, 2023 at 06:57:37PM +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@linux.alibaba.com>
> Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> ---
>  drivers/net/virtio_net.c | 36 ++++++++++++++++++++++++------------
>  1 file changed, 24 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 07b4801d689c..25b486ab74db 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1709,6 +1709,7 @@ 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);
> @@ -1717,6 +1718,8 @@ static void receive_buf(struct virtnet_info *vi, struct receive_queue *rq,
>  		return;
>  	}
>  
> +	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);

what's going on here?

> @@ -1728,19 +1731,28 @@ 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)) {
> +		if (virtnet_set_csum_after_xdp(vi, skb, flags) < 0) {
> +			pr_debug("%s: errors occurred in flow dissector setting csum",
> +				 dev->name);
> +			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;
> +	} 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;
> +		}
>  	}
>  
>  	skb_record_rx_queue(skb, vq2rxq(rq->vq));
> -- 
> 2.19.1.6.gb485710b