Commit 35d2f80b authored May 23, 2017 by Vlad Yasevich Committed by David S. Miller May 24, 2017

vlan: Fix tcp checksum offloads in Q-in-Q vlans



It appears that TCP checksum offloading has been broken for
Q-in-Q vlans.  The behavior was execerbated by the
series
    commit afb0bc97 ("Merge branch 'stacked_vlan_tso'")
that that enabled accleleration features on stacked vlans.

However, event without that series, it is possible to trigger
this issue.  It just requires a lot more specialized configuration.

The root cause is the interaction between how
netdev_intersect_features() works, the features actually set on
the vlan devices and HW having the ability to run checksum with
longer headers.

The issue starts when netdev_interesect_features() replaces
NETIF_F_HW_CSUM with a combination of NETIF_F_IP_CSUM | NETIF_F_IPV6_CSUM,
if the HW advertises IP|IPV6 specific checksums.  This happens
for tagged and multi-tagged packets.   However, HW that enables
IP|IPV6 checksum offloading doesn't gurantee that packets with
arbitrarily long headers can be checksummed.

This patch disables IP|IPV6 checksums on the packet for multi-tagged
packets.

CC: Toshiaki Makita <makita.toshiaki@lab.ntt.co.jp>
CC: Michal Kubecek <mkubecek@suse.cz>
Signed-off-by: Vladislav Yasevich <vyasevic@redhat.com>
Acked-by: Toshiaki Makita <makita.toshiaki@lab.ntt.co.jp>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent f2899788

include/linux/if_vlan.h

+10 −8

Original line number	Original line	Diff line number	Diff line
	@@ -614,14 +614,16 @@ static inline bool skb_vlan_tagged_multi(const struct sk_buff *skb)
	static inline netdev_features_t vlan_features_check(const struct sk_buff *skb,		static inline netdev_features_t vlan_features_check(const struct sk_buff *skb,
	netdev_features_t features)		netdev_features_t features)
	{		{
	if (skb_vlan_tagged_multi(skb))		if (skb_vlan_tagged_multi(skb)) {
	features = netdev_intersect_features(features,		/* In the case of multi-tagged packets, use a direct mask
	NETIF_F_SG \|		* instead of using netdev_interesect_features(), to make
	NETIF_F_HIGHDMA \|		* sure that only devices supporting NETIF_F_HW_CSUM will
	NETIF_F_FRAGLIST \|		* have checksum offloading support.
	NETIF_F_HW_CSUM \|		*/
	NETIF_F_HW_VLAN_CTAG_TX \|		features &= NETIF_F_SG \| NETIF_F_HIGHDMA \| NETIF_F_HW_CSUM \|
	NETIF_F_HW_VLAN_STAG_TX);		NETIF_F_FRAGLIST \| NETIF_F_HW_VLAN_CTAG_TX \|
			NETIF_F_HW_VLAN_STAG_TX;
			}

	return features;		return features;
	}		}

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