Re: [PATCH 08/10] tun: Re-uanble UFO support.

[Jason Wang <jasowang@redhat.com>]

On Thu, Dec 18, 2014 at 11:12 PM, Vlad Yasevich <vyasevic@redhat.com> 
wrote:
> On 12/18/2014 12:51 AM, Jason Wang wrote:
>>  
>>  
>>  ----- Original Message -----
>>>  Now that UFO is split into v4 and v6 parts, we can bring
>>>  back v4 support without any trouble.
>>> 
>>>  Continue to handle legacy applications by selecting the
>>>  IPv6 fragment id but do not change the gso type.  Thist
>>>  makes sure that two legacy VMs may still communicate.
>>> 
>>>  Based on original work from Ben Hutchings.
>>> 
>>>  Fixes: 88e0e0e5aa7a ("drivers/net: Disable UFO through virtio")
>>>  CC: Ben Hutchings <ben@decadent.org.uk>
>>>  Signed-off-by: Vladislav Yasevich <vyasevic@redhat.com>
>>>  ---
>>>   drivers/net/tun.c | 26 ++++++++++++++------------
>>>   1 file changed, 14 insertions(+), 12 deletions(-)
>>> 
>>>  diff --git a/drivers/net/tun.c b/drivers/net/tun.c
>>>  index 9dd3746..8c32fca 100644
>>>  --- a/drivers/net/tun.c
>>>  +++ b/drivers/net/tun.c
>>>  @@ -175,7 +175,7 @@ struct tun_struct {
>>>   	struct net_device	*dev;
>>>   	netdev_features_t	set_features;
>>>   #define TUN_USER_FEATURES 
>>> (NETIF_F_HW_CSUM|NETIF_F_TSO_ECN|NETIF_F_TSO| \
>>>  -			  NETIF_F_TSO6)
>>>  +			  NETIF_F_TSO6|NETIF_F_UFO)
>>>   
>>>   	int			vnet_hdr_sz;
>>>   	int			sndbuf;
>>>  @@ -1152,20 +1152,15 @@ static ssize_t tun_get_user(struct 
>>> tun_struct *tun,
>>>  struct tun_file *tfile,
>>>   			skb_shinfo(skb)->gso_type = SKB_GSO_TCPV6;
>>>   			break;
>>>   		case VIRTIO_NET_HDR_GSO_UDP:
>>>  -		{
>>>  -			static bool warned;
>>>  -
>>>  -			if (!warned) {
>>>  -				warned = true;
>>>  -				netdev_warn(tun->dev,
>>>  -					    "%s: using disabled UFO feature; please fix this 
>>> program\n",
>>>  -					    current->comm);
>>>  -			}
>>>   			skb_shinfo(skb)->gso_type = SKB_GSO_UDP;
>>>  -			if (skb->protocol == htons(ETH_P_IPV6))
>>>  +			if (vlan_get_protocol(skb) == htons(ETH_P_IPV6)) {
>>  
>>  This probably means UDPv6 with vlan does not work well, looks like 
>> another
>>  independent fixe and also for stable.
> 
> Ok.  I can split this out.
> 
>>>  +				/* This allows legacy application to work.
>>>  +				 * Do not change the gso_type as it may
>>>  +				 * not be upderstood by legacy applications.
>>>  +				 */
>>  
>>  Isn't this an issue that we use SKB_GSO_UDP for a UDPv6 packet? 
>> Especially
>>  consider we want to fix UFOv6 in the future? We probably can use
>>  SKB_GSO_UDP6 here and try to fix it in tun_put_user() if a legacy 
>> userspace
>>  is detected.
> 
> There is a slight problem with this.  This will force fragmentation 
> of IPv6
> traffic between VMs since UFO6 wouldn't be enabled on a destination 
> device.
> So, suddenly older VMs will see a performance regression for large 
> UDPv6 traffic.
> 
> 
> With this code, a legacy VM will continue to receive large UDPv6 
> traffic.
> New VMs will have an updated virtio-net which will reset the gso type 
> on input.

I get the point and that's why you still want ipv6 offload helpers to
accept SKB_GSO_UDP. So SKB_GSO_UDP was still ambigious since it can be a
UDP6 packet in fact.

I'm not sure, but probably we could just leave the regression of legacy
guest as is and fix current kernel. The sooner we eliminate the 
ambigious
the better for future development.
> 
> 
>>>   				ipv6_proxy_select_ident(skb);
>>  
>>  Question still for vlan, is network header correctly set here? 
>> Looks like
>>  ipv6_proxy_select_ident() depends on correct network header to work.
>>>  +	
> 
> Yes, you are right...  I wonder how that worked.  I'll re-test.
> 
> Thanks
> -vlad
> 		}
>>>   			break;
>>>  -		}
>>>   		default:
>>>   			tun->dev->stats.rx_frame_errors++;
>>>   			kfree_skb(skb);
>>>  @@ -1273,6 +1268,8 @@ static ssize_t tun_put_user(struct 
>>> tun_struct *tun,
>>>   				gso.gso_type = VIRTIO_NET_HDR_GSO_TCPV4;
>>>   			else if (sinfo->gso_type & SKB_GSO_TCPV6)
>>>   				gso.gso_type = VIRTIO_NET_HDR_GSO_TCPV6;
>>>  +			else if (sinfo->gso_type & SKB_GSO_UDP)
>>>  +				gso.gso_type = VIRTIO_NET_HDR_GSO_UDP;
>>>   			else {
>>>   				pr_err("unexpected GSO type: "
>>>   				       "0x%x, gso_size %d, hdr_len %d\n",
>>>  @@ -1780,6 +1777,11 @@ static int set_offload(struct tun_struct 
>>> *tun,
>>>  unsigned long arg)
>>>   				features |= NETIF_F_TSO6;
>>>   			arg &= ~(TUN_F_TSO4|TUN_F_TSO6);
>>>   		}
>>>  +
>>>  +		if (arg & TUN_F_UFO) {
>>>  +			features |= NETIF_F_UFO;
>>>  +			arg &= ~TUN_F_UFO;
>>>  +		}
>>>   	}
>>>   
>>>   	/* This gives the user a way to test for new features in future 
>>> by
>>>  --
>>>  1.9.3
>>> 
>>>  --
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>