linux-kernel - [RFC PATCH net-next 5/6] net: dsa: allow matchall mirroring rules towards the CPU

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Message-Id: <20240913152915.2981126-6-vladimir.oltean@nxp.com>
Date: Fri, 13 Sep 2024 18:29:14 +0300
From: Vladimir Oltean <vladimir.oltean@....com>
To: netdev@...r.kernel.org
Cc: "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Andrew Lunn <andrew@...n.ch>,
	Florian Fainelli <f.fainelli@...il.com>,
	Petr Machata <petrm@...dia.com>,
	Ido Schimmel <idosch@...dia.com>,
	Claudiu Manoil <claudiu.manoil@....com>,
	Alexandre Belloni <alexandre.belloni@...tlin.com>,
	UNGLinuxDriver@...rochip.com,
	Jamal Hadi Salim <jhs@...atatu.com>,
	Cong Wang <xiyou.wangcong@...il.com>,
	Jiri Pirko <jiri@...nulli.us>,
	linux-kernel@...r.kernel.org
Subject: [RFC PATCH net-next 5/6] net: dsa: allow matchall mirroring rules towards the CPU

If the CPU bandwidth capacity permits, it may be useful to mirror the
entire ingress of a user port to software.

This is in fact possible to express even if there is no net_device
representation for the CPU port. In fact, that representation wouldn't
have even helped.

The idea behind implementing this is that currently, we refuse to
offload any mirroring towards a non-DSA target net_device. But if we
acknowledge the fact that to reach any foreign net_device, the switch
must send the packet to the CPU anyway, then we can simply offload just
that part, and let the software do the rest.

Example:

$ ip link add dummy0 type dummy; ip link set dummy0 up
$ tc qdisc add dev swp0 clsact
$ tc filter add dev swp0 ingress matchall action mirred ingress mirror dev dummy0

Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
---
 net/dsa/user.c | 31 +++++++++++++++++++++++++------
 1 file changed, 25 insertions(+), 6 deletions(-)

diff --git a/net/dsa/user.c b/net/dsa/user.c
index c8ddbe22d647..bd3e3944931e 100644
--- a/net/dsa/user.c
+++ b/net/dsa/user.c
@@ -1365,7 +1365,7 @@ dsa_user_mall_tc_entry_find(struct net_device *dev, unsigned long cookie)
 static int
 dsa_user_add_cls_matchall_mirred(struct net_device *dev,
 				 struct tc_cls_matchall_offload *cls,
-				 bool ingress)
+				 bool ingress, bool ingress_target)
 {
 	struct netlink_ext_ack *extack = cls->common.extack;
 	struct dsa_port *dp = dsa_user_to_port(dev);
@@ -1398,10 +1398,25 @@ dsa_user_add_cls_matchall_mirred(struct net_device *dev,
 	if (!act->dev)
 		return -EINVAL;
 
-	if (!dsa_user_dev_check(act->dev))
-		return -EOPNOTSUPP;
-
-	to_dp = dsa_user_to_port(act->dev);
+	if (dsa_user_dev_check(act->dev)) {
+		if (ingress_target) {
+			NL_SET_ERR_MSG_MOD(extack,
+					   "Cannot mirror to ingress of target port");
+			return -EOPNOTSUPP;
+		}
+		to_dp = dsa_user_to_port(act->dev);
+	} else {
+		/* Handle mirroring to foreign target ports as a mirror towards
+		 * the CPU. The software tc rule will take the packets from
+		 * there.
+		 */
+		if (cls->skip_sw) {
+			NL_SET_ERR_MSG_MOD(extack,
+					   "Can only mirred to CPU if filter also runs in software");
+			return -EOPNOTSUPP;
+		}
+		to_dp = dp->cpu_dp;
+	}
 
 	if (dp->ds != to_dp->ds) {
 		NL_SET_ERR_MSG_MOD(extack,
@@ -1506,7 +1521,11 @@ static int dsa_user_add_cls_matchall(struct net_device *dev,
 
 	switch (action->entries[0].id) {
 	case FLOW_ACTION_MIRRED:
-		return dsa_user_add_cls_matchall_mirred(dev, cls, ingress);
+		return dsa_user_add_cls_matchall_mirred(dev, cls, ingress,
+							false);
+	case FLOW_ACTION_MIRRED_INGRESS:
+		return dsa_user_add_cls_matchall_mirred(dev, cls, ingress,
+							true);
 	case FLOW_ACTION_POLICE:
 		return dsa_user_add_cls_matchall_police(dev, cls, ingress);
 	default:
-- 
2.34.1