Subject: NET: skip GRO for foreign MAC addresses

For network drivers using napi_gro_receive, packets are run through GRO,
even when the destination MAC address does not match, and they're supposed
to be delivered to another host behind a different bridge port.

This can be very expensive, because for drivers without TSO or scatter-
gather, this can only be undone by copying the skb and checksumming it
again.

To be able to track foreign MAC addresses in an inexpensive way, create
a mask of changed bits in MAC addresses of upper devices. This allows
handling VLANs and bridge devices with different addresses (as long as
they are not too different).

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4199,6 +4199,9 @@ static enum gro_result dev_gro_receive(s
 	enum gro_result ret;
 	int grow;
 
+	if (skb->gro_skip)
+		goto normal;
+
 	if (!(skb->dev->features & NETIF_F_GRO))
 		goto normal;
 
@@ -5349,6 +5352,48 @@ static void __netdev_adjacent_dev_unlink
 					   &upper_dev->adj_list.lower);
 }
 
+static void __netdev_addr_mask(unsigned char *mask, const unsigned char *addr,
+			       struct net_device *dev)
+{
+	int i;
+
+	for (i = 0; i < dev->addr_len; i++)
+		mask[i] |= addr[i] ^ dev->dev_addr[i];
+}
+
+static void __netdev_upper_mask(unsigned char *mask, struct net_device *dev,
+				struct net_device *lower)
+{
+	struct net_device *cur;
+	struct list_head *iter;
+
+	netdev_for_each_upper_dev_rcu(dev, cur, iter) {
+		__netdev_addr_mask(mask, cur->dev_addr, lower);
+		__netdev_upper_mask(mask, cur, lower);
+	}
+}
+
+static void __netdev_update_addr_mask(struct net_device *dev)
+{
+	unsigned char mask[MAX_ADDR_LEN];
+	struct net_device *cur;
+	struct list_head *iter;
+
+	memset(mask, 0, sizeof(mask));
+	__netdev_upper_mask(mask, dev, dev);
+	memcpy(dev->local_addr_mask, mask, dev->addr_len);
+
+	netdev_for_each_lower_dev(dev, cur, iter)
+		__netdev_update_addr_mask(cur);
+}
+
+static void netdev_update_addr_mask(struct net_device *dev)
+{
+	rcu_read_lock();
+	__netdev_update_addr_mask(dev);
+	rcu_read_unlock();
+}
+
 static int __netdev_upper_dev_link(struct net_device *dev,
 				   struct net_device *upper_dev, bool master,
 				   void *private)
@@ -5420,6 +5465,7 @@ static int __netdev_upper_dev_link(struc
 			goto rollback_lower_mesh;
 	}
 
+	netdev_update_addr_mask(dev);
 	call_netdevice_notifiers_info(NETDEV_CHANGEUPPER, dev,
 				      &changeupper_info.info);
 	return 0;
@@ -5546,6 +5592,7 @@ void netdev_upper_dev_unlink(struct net_
 	list_for_each_entry(i, &upper_dev->all_adj_list.upper, list)
 		__netdev_adjacent_dev_unlink(dev, i->dev);
 
+	netdev_update_addr_mask(dev);
 	call_netdevice_notifiers_info(NETDEV_CHANGEUPPER, dev,
 				      &changeupper_info.info);
 }
@@ -6086,6 +6133,7 @@ int dev_set_mac_address(struct net_devic
 	if (err)
 		return err;
 	dev->addr_assign_type = NET_ADDR_SET;
+	netdev_update_addr_mask(dev);
 	call_netdevice_notifiers(NETDEV_CHANGEADDR, dev);
 	add_device_randomness(dev->dev_addr, dev->addr_len);
 	return 0;
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -1637,6 +1637,8 @@ struct net_device {
 	struct netdev_hw_addr_list	mc;
 	struct netdev_hw_addr_list	dev_addrs;
 
+	unsigned char		local_addr_mask[MAX_ADDR_LEN];
+
 #ifdef CONFIG_SYSFS
 	struct kset		*queues_kset;
 #endif
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -641,7 +641,8 @@ struct sk_buff {
 	__u8			ipvs_property:1;
 	__u8			inner_protocol_type:1;
 	__u8			remcsum_offload:1;
-	/* 3 or 5 bit hole */
+	__u8			gro_skip:1;
+	/* 2 or 4 bit hole */
 
 #ifdef CONFIG_NET_SCHED
 	__u16			tc_index;	/* traffic control index */
--- a/net/ethernet/eth.c
+++ b/net/ethernet/eth.c
@@ -140,6 +140,18 @@ u32 eth_get_headlen(void *data, unsigned
 }
 EXPORT_SYMBOL(eth_get_headlen);
 
+static inline bool
+eth_check_local_mask(const void *addr1, const void *addr2, const void *mask)
+{
+	const u16 *a1 = addr1;
+	const u16 *a2 = addr2;
+	const u16 *m = mask;
+
+	return (((a1[0] ^ a2[0]) & ~m[0]) |
+		((a1[1] ^ a2[1]) & ~m[1]) |
+		((a1[2] ^ a2[2]) & ~m[2]));
+}
+
 /**
  * eth_type_trans - determine the packet's protocol ID.
  * @skb: received socket data
@@ -168,8 +180,12 @@ __be16 eth_type_trans(struct sk_buff *sk
 			skb->pkt_type = PACKET_MULTICAST;
 	}
 	else if (unlikely(!ether_addr_equal_64bits(eth->h_dest,
-						   dev->dev_addr)))
+						   dev->dev_addr))) {
 		skb->pkt_type = PACKET_OTHERHOST;
+		if (eth_check_local_mask(eth->h_dest, dev->dev_addr,
+					 dev->local_addr_mask))
+			skb->gro_skip = 1;
+	}
 
 	/*
 	 * Some variants of DSA tagging don't have an ethertype field