Merge branch 'dsa-flow-dissection'

John Crispin says:

====================
net-next: dsa: fix flow dissection

RPS and probably other kernel features are currently broken on some if not
all DSA devices. The root cause of this is that skb_hash will call the
flow_dissector. At this point the skb still contains the magic switch
header and the skb->protocol field is not set up to the correct 802.3
value yet. By the time the tag specific code is called, removing the header
and properly setting the protocol an invalid hash is already set. In the
case of the mt7530 this will result in all flows always having the same
hash.

Changes since RFC:
* use a callback instead of static values
* add cover letter
====================

Reviewed-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/dsa.h

@@ -101,6 +101,15 @@ struct dsa_platform_data {
 
 struct packet_type;
 
+struct dsa_device_ops {
+	struct sk_buff *(*xmit)(struct sk_buff *skb, struct net_device *dev);
+	struct sk_buff *(*rcv)(struct sk_buff *skb, struct net_device *dev,
+			       struct packet_type *pt,
+			       struct net_device *orig_dev);
+	int (*flow_dissect)(const struct sk_buff *skb, __be16 *proto,
+			    int *offset);
+};
+
 struct dsa_switch_tree {
 	struct list_head	list;
 

net/core/flow_dissector.c

@@ -4,6 +4,7 @@
 #include <linux/ip.h>
 #include <linux/ipv6.h>
 #include <linux/if_vlan.h>
+#include <net/dsa.h>
 #include <net/ip.h>
 #include <net/ipv6.h>
 #include <net/gre.h>
@@ -440,6 +441,17 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
 			 skb->vlan_proto : skb->protocol;
 		nhoff = skb_network_offset(skb);
 		hlen = skb_headlen(skb);
+		if (unlikely(netdev_uses_dsa(skb->dev))) {
+			const struct dsa_device_ops *ops;
+			int offset;
+
+			ops = skb->dev->dsa_ptr->tag_ops;
+			if (ops->flow_dissect &&
+			    !ops->flow_dissect(skb, &proto, &offset)) {
+				hlen -= offset;
+				nhoff += offset;
+			}
+		}
 	}
 
 	/* It is ensured by skb_flow_dissector_init() that control key will

net/dsa/dsa_priv.h

@@ -65,13 +65,6 @@ struct dsa_notifier_vlan_info {
 	int port;
 };
 
-struct dsa_device_ops {
-	struct sk_buff *(*xmit)(struct sk_buff *skb, struct net_device *dev);
-	struct sk_buff *(*rcv)(struct sk_buff *skb, struct net_device *dev,
-			       struct packet_type *pt,
-			       struct net_device *orig_dev);
-};
-
 struct dsa_slave_priv {
 	/* Copy of dp->ds->dst->tag_ops->xmit for faster access in hot path */
 	struct sk_buff *	(*xmit)(struct sk_buff *skb,

net/dsa/tag_mtk.c

@@ -87,7 +87,17 @@ static struct sk_buff *mtk_tag_rcv(struct sk_buff *skb, struct net_device *dev,
 	return skb;
 }
 
+static int mtk_tag_flow_dissect(const struct sk_buff *skb, __be16 *proto,
+				int *offset)
+{
+	*offset = 4;
+	*proto = ((__be16 *)skb->data)[1];
+
+	return 0;
+}
+
 const struct dsa_device_ops mtk_netdev_ops = {
-	.xmit	= mtk_tag_xmit,
-	.rcv	= mtk_tag_rcv,
+	.xmit		= mtk_tag_xmit,
+	.rcv		= mtk_tag_rcv,
+	.flow_dissect	= mtk_tag_flow_dissect,
 };