p4tc: add P4 classifier

Introduce P4 tc classifier. A tc filter instantiated on this classifier
is used to bind a P4 pipeline to one or more netdev ports. To use P4
classifier you must specify a pipeline name that will be associated to
this filter, a s/w parser and datapath ebpf program. The pipeline must have
already been created via a template.
For example, if we were to add a filter to ingress of network interface
device $P0 and associate it to P4 pipeline simple_l3 we'd issue the
following command:

tc filter add dev $P0 parent ffff: protocol all prio 6 p4 pname simple_l3 \
    action bpf obj $PARSER.o section prog/tc-parser \
    action bpf obj $PROGNAME.o section prog/tc-ingress

$PROGNAME.o and $PARSER.o is a compilation of the eBPF programs generated
by the P4 compiler and will be the representation of the P4 program.
Note that filter understands that $PARSER.o is a parser to be loaded
at the tc level. The datapath program is merely an eBPF action.

Note we do support a distinct way of loading the parser as opposed to
making it be an action, the above example would be:

tc filter add dev $P0 parent ffff: protocol all prio 6 p4 pname simple_l3 \
    prog type tc obj $PARSER.o ... \
    action bpf obj $PROGNAME.o section prog/tc-ingress

We support two types of loadings of these initial programs in the pipeline
and differentiate between what gets loaded at tc vs xdp by using syntax of

either "prog type tc obj" or "prog type xdp obj"

For XDP:

tc filter add dev $P0 ingress protocol all prio 1 p4 pname simple_l3 \
    prog type xdp obj $PARSER.o section parser/xdp \
    pinned_link /sys/fs/bpf/mylink \
    action bpf obj $PROGNAME.o section prog/tc-ingress

The theory of operations is as follows:

================================1. PARSING================================

The packet first encounters the parser.
The parser is implemented in ebpf residing either at the TC or XDP
level. The parsed header values are stored in a shared eBPF map.
When the parser runs at XDP level, we load it into XDP using tc filter
command and pin it to a file.

=============================2. ACTIONS=============================

In the above example, the P4 program (minus the parser) is encoded in an
action($PROGNAME.o). It should be noted that classical tc actions
continue to work:
IOW, someone could decide to add a mirred action to mirror all packets
after or before the ebpf action.

tc filter add dev $P0 parent ffff: protocol all prio 6 p4 pname simple_l3 \
    prog type tc obj $PARSER.o section parser/tc-ingress \
    action bpf obj $PROGNAME.o section prog/tc-ingress \
    action mirred egress mirror index 1 dev $P1 \
    action bpf obj $ANOTHERPROG.o section mysect/section-1

It should also be noted that it is feasible to split some of the ingress
datapath into XDP first and more into TC later (as was shown above for
example where the parser runs at XDP level). YMMV.

Co-developed-by: Victor Nogueira <[email protected]>
Signed-off-by: Victor Nogueira <[email protected]>
Co-developed-by: Pedro Tammela <[email protected]>
Signed-off-by: Pedro Tammela <[email protected]>
Signed-off-by: Jamal Hadi Salim <[email protected]>

include/uapi/linux/pkt_cls.h

@@ -739,6 +739,24 @@ enum {
 
 #define TCA_MATCHALL_MAX (__TCA_MATCHALL_MAX - 1)
 
+/* P4 classifier */
+
+enum {
+	TCA_P4_UNSPEC,
+	TCA_P4_CLASSID,
+	TCA_P4_ACT,
+	TCA_P4_PNAME,
+	TCA_P4_PIPEID,
+	TCA_P4_PROG_FD,
+	TCA_P4_PROG_NAME,
+	TCA_P4_PROG_TYPE,
+	TCA_P4_PROG_ID,
+	TCA_P4_PAD,
+	__TCA_P4_MAX,
+};
+
+#define TCA_P4_MAX (__TCA_P4_MAX - 1)
+
 /* Extended Matches */
 
 struct tcf_ematch_tree_hdr {

net/sched/Kconfig

@@ -565,6 +565,18 @@ config NET_CLS_MATCHALL
 	  To compile this code as a module, choose M here: the module will
 	  be called cls_matchall.
 
+config NET_CLS_P4
+	tristate "P4 classifier"
+	select NET_CLS
+	select NET_P4_TC
+	help
+	  If you say Y here, you will be able to bind a P4 pipeline
+	  program. You will need to install a P4 template representing the
+	  program successfully to use this feature.
+
+	  To compile this code as a module, choose M here: the module will
+	  be called cls_p4.
+
 config NET_EMATCH
 	bool "Extended Matches"
 	select NET_CLS

net/sched/Makefile

@@ -73,6 +73,7 @@ obj-$(CONFIG_NET_CLS_CGROUP)	+= cls_cgroup.o
 obj-$(CONFIG_NET_CLS_BPF)	+= cls_bpf.o
 obj-$(CONFIG_NET_CLS_FLOWER)	+= cls_flower.o
 obj-$(CONFIG_NET_CLS_MATCHALL)	+= cls_matchall.o
+obj-$(CONFIG_NET_CLS_P4)	+= cls_p4.o
 obj-$(CONFIG_NET_EMATCH)	+= ematch.o
 obj-$(CONFIG_NET_EMATCH_CMP)	+= em_cmp.o
 obj-$(CONFIG_NET_EMATCH_NBYTE)	+= em_nbyte.o