[PATCH v3 bpf-next 6/9] bpf: cpumap: implement XDP_REDIRECT for eBPF programs attached to map entries

[Lorenzo Bianconi <lorenzo@xxxxxxxxxx>]

Introduce XDP_REDIRECT support for eBPF programs attached to cpumap
entries.
This patch has been tested on Marvell ESPRESSObin using a modified
version of xdp_redirect_cpu sample in order to attach a XDP program
to CPUMAP entries to perform a redirect on the mvneta interface.
In particular the following scenario has been tested:

rq (cpu0) --> mvneta - XDP_REDIRECT (cpu0) --> CPUMAP - XDP_REDIRECT (cpu1) --> mvneta

$./xdp_redirect_cpu -p xdp_cpu_map0 -d eth0 -c 1 -e xdp_redirect \
	-f xdp_redirect_kern.o -m tx_port -r eth0

tx: 285.2 Kpps rx: 285.2 Kpps

Attacching a simple XDP program on eth0 to perform XDP_TX gives
comparable results:

tx: 288.4 Kpps rx: 288.4 Kpps

Co-developed-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
Signed-off-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
Signed-off-by: Lorenzo Bianconi <lorenzo@xxxxxxxxxx>
---
 include/net/xdp.h          |  1 +
 include/trace/events/xdp.h |  6 ++++--
 kernel/bpf/cpumap.c        | 17 +++++++++++++++--
 3 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/include/net/xdp.h b/include/net/xdp.h
index 83b9e0142b52..5be0d4d65b94 100644
--- a/include/net/xdp.h
+++ b/include/net/xdp.h
@@ -99,6 +99,7 @@ struct xdp_frame {
 };
 
 struct xdp_cpumap_stats {
+	unsigned int redirect;
 	unsigned int pass;
 	unsigned int drop;
 };
diff --git a/include/trace/events/xdp.h b/include/trace/events/xdp.h
index e2c99f5bee39..cd24e8a59529 100644
--- a/include/trace/events/xdp.h
+++ b/include/trace/events/xdp.h
@@ -190,6 +190,7 @@ TRACE_EVENT(xdp_cpumap_kthread,
 		__field(int, sched)
 		__field(unsigned int, xdp_pass)
 		__field(unsigned int, xdp_drop)
+		__field(unsigned int, xdp_redirect)
 	),
 
 	TP_fast_assign(
@@ -201,18 +202,19 @@ TRACE_EVENT(xdp_cpumap_kthread,
 		__entry->sched	= sched;
 		__entry->xdp_pass	= xdp_stats->pass;
 		__entry->xdp_drop	= xdp_stats->drop;
+		__entry->xdp_redirect	= xdp_stats->redirect;
 	),
 
 	TP_printk("kthread"
 		  " cpu=%d map_id=%d action=%s"
 		  " processed=%u drops=%u"
 		  " sched=%d"
-		  " xdp_pass=%u xdp_drop=%u",
+		  " xdp_pass=%u xdp_drop=%u xdp_redirect=%u",
 		  __entry->cpu, __entry->map_id,
 		  __print_symbolic(__entry->act, __XDP_ACT_SYM_TAB),
 		  __entry->processed, __entry->drops,
 		  __entry->sched,
-		  __entry->xdp_pass, __entry->xdp_drop)
+		  __entry->xdp_pass, __entry->xdp_drop, __entry->xdp_redirect)
 );
 
 TRACE_EVENT(xdp_cpumap_enqueue,
diff --git a/kernel/bpf/cpumap.c b/kernel/bpf/cpumap.c
index 4e4cd240f07b..c0b2f265ccb2 100644
--- a/kernel/bpf/cpumap.c
+++ b/kernel/bpf/cpumap.c
@@ -240,7 +240,7 @@ static int cpu_map_bpf_prog_run_xdp(struct bpf_cpu_map_entry *rcpu,
 	xdp_set_return_frame_no_direct();
 	xdp.rxq = &rxq;
 
-	rcu_read_lock();
+	rcu_read_lock_bh();
 
 	prog = READ_ONCE(rcpu->prog);
 	for (i = 0; i < n; i++) {
@@ -266,6 +266,16 @@ static int cpu_map_bpf_prog_run_xdp(struct bpf_cpu_map_entry *rcpu,
 				stats->pass++;
 			}
 			break;
+		case XDP_REDIRECT:
+			err = xdp_do_redirect(xdpf->dev_rx, &xdp,
+					      prog);
+			if (unlikely(err)) {
+				xdp_return_frame(xdpf);
+				stats->drop++;
+			} else {
+				stats->redirect++;
+			}
+			break;
 		default:
 			bpf_warn_invalid_xdp_action(act);
 			/* fallthrough */
@@ -276,7 +286,10 @@ static int cpu_map_bpf_prog_run_xdp(struct bpf_cpu_map_entry *rcpu,
 		}
 	}
 
-	rcu_read_unlock();
+	if (stats->redirect)
+		xdp_do_flush_map();
+
+	rcu_read_unlock_bh(); /* resched point, may call do_softirq() */
 	xdp_clear_return_frame_no_direct();
 
 	return nframes;
-- 
2.26.2