Subject: Re: [PATCH 09/10] macvtap: Re-enable UFO support

From: "Michael S. Tsirkin" <[email-masked]>
Date: Thu, 18 Dec 2014 00:41:00 +0200

On Wed, Dec 17, 2014 at 01:20:54PM -0500, Vladislav Yasevich wrote:
> Now that UFO is split into v4 and v6 parts, we can bring
> back v4 support.  Continue to handle legacy applications
> by selecting the ipv6 fagment id but do not change the
> gso type.  This allows 2 legacy VMs to continue to communicate.
> 
> Based on original work from Ben Hutchings.
> 
> Fixes: 88e0e0e5aa7a ("drivers/net: Disable UFO through virtio")
> CC: Ben Hutchings <[email-masked]>
> Signed-off-by: Vladislav Yasevich <[email-masked]>
> ---
>  drivers/net/macvtap.c | 20 ++++++++++++++------
>  1 file changed, 14 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
> index 880cc09..75febd4 100644
> --- a/drivers/net/macvtap.c
> +++ b/drivers/net/macvtap.c
> @@ -66,7 +66,7 @@ static struct cdev macvtap_cdev;
>  static const struct proto_ops macvtap_socket_ops;
>  
>  #define TUN_OFFLOADS (NETIF_F_HW_CSUM | NETIF_F_TSO_ECN | NETIF_F_TSO | \
> -		      NETIF_F_TSO6)
> +		      NETIF_F_TSO6 | NETIF_F_UFO)
>  #define RX_OFFLOADS (NETIF_F_GRO | NETIF_F_LRO)
>  #define TAP_FEATURES (NETIF_F_GSO | NETIF_F_SG)
>  
> @@ -570,11 +570,14 @@ static int macvtap_skb_from_vnet_hdr(struct sk_buff *skb,
>  			gso_type = SKB_GSO_TCPV6;
>  			break;
>  		case VIRTIO_NET_HDR_GSO_UDP:
> -			pr_warn_once("macvtap: %s: using disabled UFO feature; please fix this program\n",
> -				     current->comm);
>  			gso_type = SKB_GSO_UDP;
> -			if (skb->protocol == htons(ETH_P_IPV6))
> +			if (vlan_get_protocol(skb) == htons(ETH_P_IPV6)) {
> +				/* This is to support legacy appliacations.
> +				 * Do not change the gso_type as legacy apps
> +				 * may not know about the new type.
> +				 */
>  				ipv6_proxy_select_ident(skb);
> +			}
>  			break;
>  		default:
>  			return -EINVAL;
> @@ -619,6 +622,8 @@ static void macvtap_skb_to_vnet_hdr(const struct sk_buff *skb,
>  			vnet_hdr->gso_type = VIRTIO_NET_HDR_GSO_TCPV4;
>  		else if (sinfo->gso_type & SKB_GSO_TCPV6)
>  			vnet_hdr->gso_type = VIRTIO_NET_HDR_GSO_TCPV6;
> +		else if (sinfo->gso_type & SKB_GSO_UDP)
> +			vnet_hdr->gso_type = VIRTIO_NET_HDR_GSO_UDP;
>  		else
>  			BUG();
>  		if (sinfo->gso_type & SKB_GSO_TCP_ECN)
> @@ -955,6 +960,9 @@ static int set_offload(struct macvtap_queue *q, unsigned long arg)
>  			if (arg & TUN_F_TSO6)
>  				feature_mask |= NETIF_F_TSO6;
>  		}
> +
> +		if (arg & TUN_F_UFO)
> +			feature_mask |= NETIF_F_UFO;
>  	}
>  
>  	/* tun/tap driver inverts the usage for TSO offloads, where
> @@ -965,7 +973,7 @@ static int set_offload(struct macvtap_queue *q, unsigned long arg)
>  	 * When user space turns off TSO, we turn off GSO/LRO so that
>  	 * user-space will not receive TSO frames.
>  	 */
> -	if (feature_mask & (NETIF_F_TSO | NETIF_F_TSO6))
> +	if (feature_mask & (NETIF_F_TSO | NETIF_F_TSO6 | NETIF_F_UFO))
>  		features |= RX_OFFLOADS;
>  	else
>  		features &= ~RX_OFFLOADS;

By the way this logic is completely broken, even without your patch,
isn't it?

It says: enable LRO+GRO if any of NETIF_F_TSO | NETIF_F_TSO6 |
NETIF_F_UFO set.

So what happens if I enable TSO only?
LRO gets enabled so I can still get TSO6 packets.

This really should be:

	if (feature_mask & (NETIF_F_TSO | NETIF_F_TSO6 | NETIF_F_UFO) ==
			(NETIF_F_TSO | NETIF_F_TSO6 | NETIF_F_UFO)

fixing this probably should be a separate patch before your
series, and Cc stable.

> @@ -1066,7 +1074,7 @@ static long macvtap_ioctl(struct file *file, unsigned int cmd,
>  	case TUNSETOFFLOAD:
>  		/* let the user check for future flags */
>  		if (arg & ~(TUN_F_CSUM | TUN_F_TSO4 | TUN_F_TSO6 |
> -			    TUN_F_TSO_ECN))
> +			    TUN_F_TSO_ECN | TUN_F_UFO))
>  			return -EINVAL;
>  
>  		rtnl_lock();
> -- 
> 1.9.3