net: sched: propagate "skip_sw" flag to struct flow_cls_common_offload

Background: switchdev ports offload the Linux bridge, and most of the
packets they handle will never see the CPU. The ports between which
there exists no hardware data path are considered 'foreign' to switchdev.
These can either be normal physical NICs without switchdev offload, or
incompatible switchdev ports, or virtual interfaces like veth/dummy/etc.

In some cases, an offloaded filter can only do half the work, and the
rest must be handled by software. Redirecting/mirroring from the ingress
of a switchdev port towards a foreign interface is one example of
combined hardware/software data path. The most that the switchdev port
can do is to extract the matching packets from its offloaded data path
and send them to the CPU. From there on, the software filter runs
(a second time, after the first run in hardware) on the packet and
performs the mirred action.

It makes sense for switchdev drivers which allow this kind of "half
offloading" to sense the "skip_sw" flag of the filter/action pair, and
deny attempts from the user to install a filter that does not run in
software, because that simply won't work.

In fact, a mirred action on a switchdev port towards a dummy interface
appears to be a valid way of (selectively) monitoring offloaded traffic
that flows through it. IFF_PROMISC was also discussed years ago, but
(despite initial disagreement) there seems to be consensus that this
flag should not affect the destination taken by packets, but merely
whether or not the NIC discards packets with unknown MAC DA for local
processing.

[1] https://lore.kernel.org/netdev/20190830092637.7f83d162@ceranb/
[2] https://lore.kernel.org/netdev/20191002233750.13566-1-olteanv@gmail.com/
Suggested-by: Ido Schimmel <idosch@nvidia.com>
Link: https://lore.kernel.org/netdev/ZxUo0Dc0M5Y6l9qF@shredder.mtl.com/
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Link: https://patch.msgid.link/20241023135251.1752488-2-vladimir.oltean@nxp.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/include/net/flow_offload.h b/include/net/flow_offload.h
index 292cd8f4b762a83729db6623242e1d4ca4e00850..596ab9791e4d40dc19e6a00f557870af0bc35eda 100644 (file)
--- a/include/net/flow_offload.h
+++ b/include/net/flow_offload.h
@@ -685,6 +685,7 @@ struct flow_cls_common_offload {
        u32 chain_index;
        __be16 protocol;
        u32 prio;
+       bool skip_sw;
        struct netlink_ext_ack *extack;
 };
 

diff --git a/include/net/pkt_cls.h b/include/net/pkt_cls.h
index 4880b3a7aced5b798311e5b7bc4dd10efecfe864..cf199af85c52e2d12874277fb7a6e088b912e50e 100644 (file)
--- a/include/net/pkt_cls.h
+++ b/include/net/pkt_cls.h
@@ -755,6 +755,7 @@ tc_cls_common_offload_init(struct flow_cls_common_offload *cls_common,
        cls_common->chain_index = tp->chain->index;
        cls_common->protocol = tp->protocol;
        cls_common->prio = tp->prio >> 16;
+       cls_common->skip_sw = tc_skip_sw(flags);
        if (tc_skip_sw(flags) || flags & TCA_CLS_FLAGS_VERBOSE)
                cls_common->extack = extack;
 }