bpf: add initial bpf tracepoints

This work adds a number of tracepoints to paths that are either
considered slow-path or exception-like states, where monitoring or
inspecting them would be desirable.

For bpf(2) syscall, tracepoints have been placed for main commands
when they succeed. In XDP case, tracepoint is for exceptions, that
is, f.e. on abnormal BPF program exit such as unknown or XDP_ABORTED
return code, or when error occurs during XDP_TX action and the packet
could not be forwarded.

Both have been split into separate event headers, and can be further
extended. Worst case, if they unexpectedly should get into our way in
future, they can also removed [1]. Of course, these tracepoints (like
any other) can be analyzed by eBPF itself, etc. Example output:

  # ./perf record -a -e bpf:* sleep 10
  # ./perf script
  sock_example  6197 [005]   283.980322:      bpf:bpf_map_create: map type=ARRAY ufd=4 key=4 val=8 max=256 flags=0
  sock_example  6197 [005]   283.980721:       bpf:bpf_prog_load: prog=a5ea8fa30ea6849c type=SOCKET_FILTER ufd=5
  sock_example  6197 [005]   283.988423:   bpf:bpf_prog_get_type: prog=a5ea8fa30ea6849c type=SOCKET_FILTER
  sock_example  6197 [005]   283.988443: bpf:bpf_map_lookup_elem: map type=ARRAY ufd=4 key=[06 00 00 00] val=[00 00 00 00 00 00 00 00]
  [...]
  sock_example  6197 [005]   288.990868: bpf:bpf_map_lookup_elem: map type=ARRAY ufd=4 key=[01 00 00 00] val=[14 00 00 00 00 00 00 00]
       swapper     0 [005]   289.338243:    bpf:bpf_prog_put_rcu: prog=a5ea8fa30ea6849c type=SOCKET_FILTER

  [1] https://lwn.net/Articles/705270/

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 9 insertions, 3 deletions

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 37db91d1a0a3..f9bf94887ff1 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -23,6 +23,7 @@
 #include <linux/virtio.h>
 #include <linux/virtio_net.h>
 #include <linux/bpf.h>
+#include <linux/bpf_trace.h>
 #include <linux/scatterlist.h>
 #include <linux/if_vlan.h>
 #include <linux/slab.h>
@@ -330,7 +331,7 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
 	return skb;
 }
 
-static void virtnet_xdp_xmit(struct virtnet_info *vi,
+static bool virtnet_xdp_xmit(struct virtnet_info *vi,
 			     struct receive_queue *rq,
 			     struct send_queue *sq,
 			     struct xdp_buff *xdp,
@@ -382,10 +383,12 @@ static void virtnet_xdp_xmit(struct virtnet_info *vi,
 			put_page(page);
 		} else /* small buffer */
 			kfree_skb(data);
-		return; // On error abort to avoid unnecessary kick
+		/* On error abort to avoid unnecessary kick */
+		return false;
 	}
 
 	virtqueue_kick(sq->vq);
+	return true;
 }
 
 static u32 do_xdp_prog(struct virtnet_info *vi,
@@ -421,11 +424,14 @@ static u32 do_xdp_prog(struct virtnet_info *vi,
 			vi->xdp_queue_pairs +
 			smp_processor_id();
 		xdp.data = buf;
-		virtnet_xdp_xmit(vi, rq, &vi->sq[qp], &xdp, data);
+		if (unlikely(!virtnet_xdp_xmit(vi, rq, &vi->sq[qp], &xdp,
+					       data)))
+			trace_xdp_exception(vi->dev, xdp_prog, act);
 		return XDP_TX;
 	default:
 		bpf_warn_invalid_xdp_action(act);
 	case XDP_ABORTED:
+		trace_xdp_exception(vi->dev, xdp_prog, act);
 	case XDP_DROP:
 		return XDP_DROP;
 	}