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Subject[PATCH 4.4 26/53] vlan: Fix tcp checksum offloads in Q-in-Q vlans
Date
4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Vlad Yasevich <vyasevich@gmail.com>

commit 35d2f80b07bbe03fb358afb0bdeff7437a7d67ff upstream.

It appears that TCP checksum offloading has been broken for
Q-in-Q vlans. The behavior was execerbated by the
series
commit afb0bc972b52 ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
include/linux/if_vlan.h | 19 ++++++++++---------
1 file changed, 10 insertions(+), 9 deletions(-)

--- a/include/linux/if_vlan.h
+++ b/include/linux/if_vlan.h
@@ -616,15 +616,16 @@ static inline bool skb_vlan_tagged_multi
static inline netdev_features_t vlan_features_check(const struct sk_buff *skb,
netdev_features_t features)
{
- if (skb_vlan_tagged_multi(skb))
- features = netdev_intersect_features(features,
- NETIF_F_SG |
- NETIF_F_HIGHDMA |
- NETIF_F_FRAGLIST |
- NETIF_F_GEN_CSUM |
- NETIF_F_HW_VLAN_CTAG_TX |
- NETIF_F_HW_VLAN_STAG_TX);
-
+ if (skb_vlan_tagged_multi(skb)) {
+ /* In the case of multi-tagged packets, use a direct mask
+ * instead of using netdev_interesect_features(), to make
+ * sure that only devices supporting NETIF_F_HW_CSUM will
+ * have checksum offloading support.
+ */
+ features &= NETIF_F_SG | NETIF_F_HIGHDMA | NETIF_F_HW_CSUM |
+ NETIF_F_FRAGLIST | NETIF_F_HW_VLAN_CTAG_TX |
+ NETIF_F_HW_VLAN_STAG_TX;
+ }
return features;
}


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