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

From: Marcelo Ricardo Leitner <[email-masked]>
Date: Wed, 2 May 2018 11:14:13 -0300

On Wed, May 02, 2018 at 06:16:45AM +0300, Michael S. Tsirkin wrote:
> 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 ?

csum_not_inet is following the nomenclature used in sk_buff. Initially
Davide had named the sk_buff field after crc32c but then it was argued
that maybe another check method may be introduced later and the name
would be bogus, thus why the "csum_not_inet".

>
> >  	__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
> --
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