net: propagate NETIF_F_HIGHDMA to vlans

Automatically allows vlans to get NETIF_F_HIGHDMA if underlying device
supports it.

On 32bit arches (and more precisely if CONFIG_HIGHMEM is enabled), it
can help to reduce cost of illegal_highdma() and __skb_linearize()
calls.

Tested on tg3 , bnx2, bonding, this worked very well.

This is a generalization of a patch provided by Yi Zou & Jeff Kirsher.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 3 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index 2c7934f8cf3e..e0c0b86f57a1 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -5058,10 +5058,11 @@ int register_netdevice(struct net_device *dev)
         if (dev->features & NETIF_F_SG)
                 dev->features |= NETIF_F_GSO;
 
-        /* Enable GRO for vlans by default if dev->features has GRO also.
-         * vlan_dev_init() will do the dev->features check.
+        /* Enable GRO and NETIF_F_HIGHDMA for vlans by default,
+         * vlan_dev_init() will do the dev->features check, so these features
+         * are enabled only if supported by underlying device.
          */
-        dev->vlan_features |= NETIF_F_GRO;
+        dev->vlan_features |= (NETIF_F_GRO | NETIF_F_HIGHDMA);
 
         ret = call_netdevice_notifiers(NETDEV_POST_INIT, dev);
         ret = notifier_to_errno(ret);