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

From: "Michael S. Tsirkin" <[email-masked]>
Date: Thu, 18 Dec 2014 09:55:49 +0200

On Wed, Dec 17, 2014 at 09:43:51PM -0500, Vlad Yasevich wrote:
> On 12/17/2014 05:41 PM, Michael S. Tsirkin wrote:
> > 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.
> 
> Actually, all this LRO/GRO feature manipulation on the macvtap device is
> rather pointless as those features aren't really checked at any point
> on the macvtap receive path.  GRO calls are done from napi context on
> the lowest device, so by the time a packet hits macvtap, GRO/LRO has
> already been done.
> 
> So it doesn't really matter that we disable them incorrectly.  I
> can send a separate patch to clean this up.

Hmm so if userspace says it can't handle TSO packets,
it might get them anyway?

> > 
> > 
> >> @@ -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