Re: [PATCH net-next 1/5] virtio: Add support for SCTP checksum offloading

[Vlad Yasevich <vyasevic@redhat.com>]

On 04/11/2018 06:49 PM, Michael S. Tsirkin wrote:
> On Mon, Apr 02, 2018 at 09:40:02AM -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 signalling to the guest that an alternate checksum needs to
>> be used is done via a new flag in the virtio_net_hdr.  If the
>> flag is set, the host will know to perform an alternate checksum
>> calculation, which right now is only CRC32c.
>>
>> Signed-off-by: Vladislav Yasevich <vyasevic@redhat.com>
>> ---
>>  drivers/net/virtio_net.c        | 11 ++++++++---
>>  include/linux/virtio_net.h      |  6 ++++++
>>  include/uapi/linux/virtio_net.h |  2 ++
>>  3 files changed, 16 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>> index 7b187ec..b601294 100644
>> --- a/drivers/net/virtio_net.c
>> +++ b/drivers/net/virtio_net.c
>> @@ -2724,9 +2724,14 @@ 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;
>> +		netdev_features_t sctp = 0;
>> +
>> +		if (virtio_has_feature(vdev, VIRTIO_NET_F_SCTP_CSUM))
>> +			sctp |= NETIF_F_SCTP_CRC;
>> +
>> +		dev->hw_features |= NETIF_F_HW_CSUM | NETIF_F_SG | sctp;
>>  		if (csum)
>> -			dev->features |= NETIF_F_HW_CSUM | NETIF_F_SG;
>> +			dev->features |= NETIF_F_HW_CSUM | NETIF_F_SG | sctp;
>>  
>>  		if (virtio_has_feature(vdev, VIRTIO_NET_F_GSO)) {
>>  			dev->hw_features |= NETIF_F_TSO
>> @@ -2952,7 +2957,7 @@ static struct virtio_device_id id_table[] = {
>>  };
>>  
>>  #define VIRTNET_FEATURES \
>> -	VIRTIO_NET_F_CSUM, VIRTIO_NET_F_GUEST_CSUM, \
>> +	VIRTIO_NET_F_CSUM, VIRTIO_NET_F_GUEST_CSUM,  VIRTIO_NET_F_SCTP_CSUM, \
>>  	VIRTIO_NET_F_MAC, \
>>  	VIRTIO_NET_F_HOST_TSO4, VIRTIO_NET_F_HOST_UFO, VIRTIO_NET_F_HOST_TSO6, \
>>  	VIRTIO_NET_F_HOST_ECN, VIRTIO_NET_F_GUEST_TSO4, VIRTIO_NET_F_GUEST_TSO6, \
>> diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h
>> index f144216..2e7a64a 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) {
>> @@ -96,6 +99,9 @@ static inline int virtio_net_hdr_from_skb(const struct sk_buff *skb,
>>  		hdr->flags = VIRTIO_NET_HDR_F_DATA_VALID;
>>  	} /* else everything is zero */
>>  
>> +	if (skb->csum_not_inet)
>> +		hdr->flags &= VIRTIO_NET_HDR_F_CSUM_NOT_INET;
>> +
>>  	return 0;
>>  }
>>  
>> diff --git a/include/uapi/linux/virtio_net.h b/include/uapi/linux/virtio_net.h
>> index 5de6ed3..3f279c8 100644
>> --- a/include/uapi/linux/virtio_net.h
>> +++ b/include/uapi/linux/virtio_net.h
>> @@ -36,6 +36,7 @@
>>  #define VIRTIO_NET_F_GUEST_CSUM	1	/* Guest handles pkts w/ partial csum */
>>  #define VIRTIO_NET_F_CTRL_GUEST_OFFLOADS 2 /* Dynamic offload configuration. */
>>  #define VIRTIO_NET_F_MTU	3	/* Initial MTU advice */
>> +#define VIRTIO_NET_F_SCTP_CSUM  4	/* SCTP checksum offload support */
>>  #define VIRTIO_NET_F_MAC	5	/* Host has given MAC address. */
>>  #define VIRTIO_NET_F_GUEST_TSO4	7	/* Guest can handle TSOv4 in. */
>>  #define VIRTIO_NET_F_GUEST_TSO6	8	/* Guest can handle TSOv6 in. */
> 
> Is this a guest or a host checksum? We should differenciate between the
> two.

I suppose this is HOST checksum, since it behaves like VIRTIO_NET_F_CSUM only for
SCTP.  I couldn't find the use for the GUEST side flag, since there technically
isn't any validations and there is no additional mappings from VIRTIO flag to a
NETIF flag.

If the feature is negotiated, the guest ends up generating partially check-summed
packets, and the host turns on appropriate flags on it's side.   The host will
also make sure the checksum if fixed up if the guest doesn't support it.
So 1 flag is currently all that is needed.

-vlad

> 
> 
>> @@ -101,6 +102,7 @@ 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 */
>>  	__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