Subject: Re: [PATCH V2 net-next 1/6] virtio: Add support for SCTP checksum offloading

From: "Michael S. Tsirkin" <[email-masked]>
Date: Wed, 2 May 2018 06:16:45 +0300

On Tue, May 01, 2018 at 10:07:34PM -0400, Vladislav Yasevich wrote:
> To support SCTP checksum offloading, we need to add a new feature
> to virtio_net, so we can negotiate support between the hypervisor
> and the guest.
> The HOST feature bit signifies offloading support for transmit and
> enables device offload features.
> The GUEST feature bit signifies offloading support of recieve and
> is currently only used by the driver in case of xdp.  
> 
> That patch also adds an addition virtio_net header flag which
> mirrors the skb->csum_not_inet flag.  This flags is used to indicate
> that is this an SCTP packet that needs its checksum computed by the
> lower layer.  In this case, the lower layer is the host hypervisor or
> possibly HW nic that supporst CRC32c offload.
> 
> In the case that GUEST feature bit is flag, it will be possible to
> receive a virtio_net header with this bit set, which will set the
> corresponding skb bit.  SCTP protocol will be updated to correctly
> deal with it.
> 
> Signed-off-by: Vladislav Yasevich <[email-masked]>
> ---
>  drivers/net/virtio_net.c        | 14 +++++++++++++-
>  include/linux/virtio_net.h      |  6 ++++++
>  include/uapi/linux/virtio_net.h |  5 +++++
>  3 files changed, 24 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 7b187ec..34af280 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -2148,6 +2148,8 @@ static int virtnet_clear_guest_offloads(struct virtnet_info *vi)
>  
>  	if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_CSUM))
>  		offloads = 1ULL << VIRTIO_NET_F_GUEST_CSUM;
> +	if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_SCTP_CSUM))
> +		offloads |= 1ULL << VIRTIO_NET_F_GUEST_SCTP_CSUM;
>  
>  	return virtnet_set_guest_offloads(vi, offloads);
>  }
> @@ -2160,6 +2162,8 @@ static int virtnet_restore_guest_offloads(struct virtnet_info *vi)
>  		return 0;
>  	if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_CSUM))
>  		offloads |= 1ULL << VIRTIO_NET_F_GUEST_CSUM;
> +	if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_SCTP_CSUM))
> +		offloads |= 1ULL << VIRTIO_NET_F_GUEST_SCTP_CSUM;
>  
>  	return virtnet_set_guest_offloads(vi, offloads);
>  }
> @@ -2724,6 +2728,7 @@ static int virtnet_probe(struct virtio_device *vdev)
>  	/* Do we support "hardware" checksums? */
>  	if (virtio_has_feature(vdev, VIRTIO_NET_F_CSUM)) {
>  		/* This opens up the world of extra features. */
> +
>  		dev->hw_features |= NETIF_F_HW_CSUM | NETIF_F_SG;
>  		if (csum)
>  			dev->features |= NETIF_F_HW_CSUM | NETIF_F_SG;
> @@ -2746,9 +2751,15 @@ static int virtnet_probe(struct virtio_device *vdev)
>  			dev->features |= dev->hw_features & NETIF_F_ALL_TSO;
>  		/* (!csum && gso) case will be fixed by register_netdev() */
>  	}
> +
>  	if (virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_CSUM))
>  		dev->features |= NETIF_F_RXCSUM;
>  
> +	if (virtio_has_feature(vdev, VIRTIO_NET_F_HOST_SCTP_CSUM)) {
> +		dev->hw_features |= NETIF_F_SCTP_CRC;
> +		dev->features |= NETIF_F_SCTP_CRC;
> +	}
> +
>  	dev->vlan_features = dev->features;
>  
>  	/* MTU range: 68 - 65535 */
> @@ -2962,7 +2973,8 @@ static struct virtio_device_id id_table[] = {
>  	VIRTIO_NET_F_GUEST_ANNOUNCE, VIRTIO_NET_F_MQ, \
>  	VIRTIO_NET_F_CTRL_MAC_ADDR, \
>  	VIRTIO_NET_F_MTU, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS, \
> -	VIRTIO_NET_F_SPEED_DUPLEX
> +	VIRTIO_NET_F_SPEED_DUPLEX, \
> +	VIRTIO_NET_F_HOST_SCTP_CSUM, VIRTIO_NET_F_GUEST_SCTP_CSUM
>  
>  static unsigned int features[] = {
>  	VIRTNET_FEATURES,
> diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h
> index f144216..28fffdc 100644
> --- a/include/linux/virtio_net.h
> +++ b/include/linux/virtio_net.h
> @@ -39,6 +39,9 @@ static inline int virtio_net_hdr_to_skb(struct sk_buff *skb,
>  
>  		if (!skb_partial_csum_set(skb, start, off))
>  			return -EINVAL;
> +
> +		if (hdr->flags & VIRTIO_NET_HDR_F_CSUM_NOT_INET)
> +			skb->csum_not_inet = 1;
>  	}
>  
>  	if (hdr->gso_type != VIRTIO_NET_HDR_GSO_NONE) {
> @@ -91,6 +94,9 @@ static inline int virtio_net_hdr_from_skb(const struct sk_buff *skb,
>  				skb_checksum_start_offset(skb));
>  		hdr->csum_offset = __cpu_to_virtio16(little_endian,
>  				skb->csum_offset);
> +
> +		if (skb->csum_not_inet)
> +			hdr->flags |= VIRTIO_NET_HDR_F_CSUM_NOT_INET;
>  	} else if (has_data_valid &&
>  		   skb->ip_summed == CHECKSUM_UNNECESSARY) {
>  		hdr->flags = VIRTIO_NET_HDR_F_DATA_VALID;
> diff --git a/include/uapi/linux/virtio_net.h b/include/uapi/linux/virtio_net.h
> index 5de6ed3..9dfca1a 100644
> --- a/include/uapi/linux/virtio_net.h
> +++ b/include/uapi/linux/virtio_net.h
> @@ -57,6 +57,10 @@
>  					 * Steering */
>  #define VIRTIO_NET_F_CTRL_MAC_ADDR 23	/* Set MAC address */
>  
> +#define VIRTIO_NET_F_GUEST_SCTP_CSUM  61 /* Guest handles SCTP pks w/ partial
> +					  * csum */
> +#define VIRTIO_NET_F_HOST_SCTP_CSUM   62 /* HOST handles SCTP pkts w/ partial
> +					  * csum */
>  #define VIRTIO_NET_F_SPEED_DUPLEX 63	/* Device set linkspeed and duplex */
>  
>  #ifndef VIRTIO_NET_NO_LEGACY
> @@ -101,6 +105,7 @@ struct virtio_net_config {
>  struct virtio_net_hdr_v1 {
>  #define VIRTIO_NET_HDR_F_NEEDS_CSUM	1	/* Use csum_start, csum_offset */
>  #define VIRTIO_NET_HDR_F_DATA_VALID	2	/* Csum is valid */
> +#define VIRTIO_NET_HDR_F_CSUM_NOT_INET  4       /* Checksum is not inet */

Both comment and name are not very informative.
How about just saying CRC32c ?

>  	__u8 flags;
>  #define VIRTIO_NET_HDR_GSO_NONE		0	/* Not a GSO frame */
>  #define VIRTIO_NET_HDR_GSO_TCPV4	1	/* GSO frame, IPv4 TCP (TSO) */
> -- 
> 2.9.5