Subject: Re: [PATCH net-next V2 5/5] virtio-net: switch off offloads on demand if possible on XDP set

From: "Michael S. Tsirkin" <[email-masked]>
Date: Tue, 25 Jul 2017 00:29:21 +0300

On Wed, Jul 19, 2017 at 04:54:49PM +0800, Jason Wang wrote:
> Current XDP implementation wants guest offloads feature to be disabled
> on device. This is inconvenient and means guest can't benefit from
> offloads if XDP is not used. This patch tries to address this
> limitation by disabling the offloads on demand through control guest
> offloads. Guest offloads will be disabled and enabled on demand on XDP
> set.
> 
> Signed-off-by: Jason Wang <[email-masked]>

Doesn't look like my comments on v1 were addressed.
Copying here:

In fact, since we no longer reset when XDP is set,
here device might have offloads enabled, buffers are
used but not consumed, then XDP is set.

This can result in
- packet scattered across multiple buffers
  (handled correctly but need to update the comment)
- packet may have VIRTIO_NET_HDR_F_NEEDS_CSUM, in that case
  the spec says "The checksum on the packet is incomplete".
  (probably needs to be handled by calculating the checksum).

Jason, as David applied this patch already, can you comment
on the issues please?

> ---
>  drivers/net/virtio_net.c | 70 ++++++++++++++++++++++++++++++++++++++++++++----
>  1 file changed, 65 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index b3fc01d..5fbd15e 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -57,6 +57,11 @@ DECLARE_EWMA(pkt_len, 0, 64)
>  
>  #define VIRTNET_DRIVER_VERSION "1.0.0"
>  
> +const unsigned long guest_offloads[] = { VIRTIO_NET_F_GUEST_TSO4,
> +					 VIRTIO_NET_F_GUEST_TSO6,
> +					 VIRTIO_NET_F_GUEST_ECN,
> +					 VIRTIO_NET_F_GUEST_UFO };
> +
>  struct virtnet_stats {
>  	struct u64_stats_sync tx_syncp;
>  	struct u64_stats_sync rx_syncp;
> @@ -164,10 +169,13 @@ struct virtnet_info {
>  	u8 ctrl_promisc;
>  	u8 ctrl_allmulti;
>  	u16 ctrl_vid;
> +	u64 ctrl_offloads;
>  
>  	/* Ethtool settings */
>  	u8 duplex;
>  	u32 speed;
> +
> +	unsigned long guest_offloads;
>  };
>  
>  struct padded_vnet_hdr {
> @@ -1896,6 +1904,47 @@ static int virtnet_restore_up(struct virtio_device *vdev)
>  	return err;
>  }
>  
> +static int virtnet_set_guest_offloads(struct virtnet_info *vi, u64 offloads)
> +{
> +	struct scatterlist sg;
> +	vi->ctrl_offloads = cpu_to_virtio64(vi->vdev, offloads);
> +
> +	sg_init_one(&sg, &vi->ctrl_offloads, sizeof(vi->ctrl_offloads));
> +
> +	if (!virtnet_send_command(vi, VIRTIO_NET_CTRL_GUEST_OFFLOADS,
> +				  VIRTIO_NET_CTRL_GUEST_OFFLOADS_SET, &sg)) {
> +		dev_warn(&vi->dev->dev, "Fail to set guest offload. \n");
> +		return -EINVAL;
> +	}
> +
> +	return 0;
> +}
> +
> +static int virtnet_clear_guest_offloads(struct virtnet_info *vi)
> +{
> +	u64 offloads = 0;
> +
> +	if (!vi->guest_offloads)
> +		return 0;
> +
> +	if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_CSUM))
> +		offloads = 1ULL << VIRTIO_NET_F_GUEST_CSUM;
> +
> +	return virtnet_set_guest_offloads(vi, offloads);
> +}
> +
> +static int virtnet_restore_guest_offloads(struct virtnet_info *vi)
> +{
> +	u64 offloads = vi->guest_offloads;
> +
> +	if (!vi->guest_offloads)
> +		return 0;
> +	if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_CSUM))
> +		offloads |= 1ULL << VIRTIO_NET_F_GUEST_CSUM;
> +
> +	return virtnet_set_guest_offloads(vi, offloads);
> +}
> +
>  static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog,
>  			   struct netlink_ext_ack *extack)
>  {
> @@ -1905,10 +1954,11 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog,
>  	u16 xdp_qp = 0, curr_qp;
>  	int i, err;
>  
> -	if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_TSO4) ||
> -	    virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_TSO6) ||
> -	    virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_ECN) ||
> -	    virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_UFO)) {
> +	if (!virtio_has_feature(vi->vdev, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS)
> +	    && (virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_TSO4) ||
> +	        virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_TSO6) ||
> +	        virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_ECN) ||
> +		virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_UFO))) {
>  		NL_SET_ERR_MSG_MOD(extack, "Can't set XDP while host is implementing LRO, disable LRO first");
>  		return -EOPNOTSUPP;
>  	}
> @@ -1955,6 +2005,12 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog,
>  	for (i = 0; i < vi->max_queue_pairs; i++) {
>  		old_prog = rtnl_dereference(vi->rq[i].xdp_prog);
>  		rcu_assign_pointer(vi->rq[i].xdp_prog, prog);
> +		if (i == 0) {
> +			if (!old_prog)
> +				virtnet_clear_guest_offloads(vi);
> +			if (!prog)
> +				virtnet_restore_guest_offloads(vi);
> +		}
>  		if (old_prog)
>  			bpf_prog_put(old_prog);
>  		virtnet_napi_enable(vi->rq[i].vq, &vi->rq[i].napi);
> @@ -2588,6 +2644,10 @@ static int virtnet_probe(struct virtio_device *vdev)
>  		netif_carrier_on(dev);
>  	}
>  
> +	for (i = 0; i < ARRAY_SIZE(guest_offloads); i++)
> +		if (virtio_has_feature(vi->vdev, guest_offloads[i]))
> +			set_bit(guest_offloads[i], &vi->guest_offloads);
> +
>  	pr_debug("virtnet: registered device %s with %d RX and TX vq's\n",
>  		 dev->name, max_queue_pairs);
>  
> @@ -2684,7 +2744,7 @@ static struct virtio_device_id id_table[] = {
>  	VIRTIO_NET_F_CTRL_RX, VIRTIO_NET_F_CTRL_VLAN, \
>  	VIRTIO_NET_F_GUEST_ANNOUNCE, VIRTIO_NET_F_MQ, \
>  	VIRTIO_NET_F_CTRL_MAC_ADDR, \
> -	VIRTIO_NET_F_MTU
> +	VIRTIO_NET_F_MTU, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS
>  
>  static unsigned int features[] = {
>  	VIRTNET_FEATURES,
> -- 
> 2.7.4