bpf: offload: allow offloaded programs to use perf event arrays

BPF_MAP_TYPE_PERF_EVENT_ARRAY is special as far as offload goes.
The map only holds glue to perf ring, not actual data.  Allow
non-offloaded perf event arrays to be used in offloaded programs.
Offload driver can extract the events from HW and put them in
the map for user space to retrieve.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Reviewed-by: Jiong Wang <jiong.wang@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
diff --git a/kernel/bpf/offload.c b/kernel/bpf/offload.c
index c940107..ac747d5 100644
--- a/kernel/bpf/offload.c
+++ b/kernel/bpf/offload.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2017 Netronome Systems, Inc.
+ * Copyright (C) 2017-2018 Netronome Systems, Inc.
  *
  * This software is licensed under the GNU General License Version 2,
  * June 1991 as shown in the file COPYING in the top-level directory of this
@@ -474,8 +474,10 @@ bool bpf_offload_dev_match(struct bpf_prog *prog, struct bpf_map *map)
 	struct bpf_prog_offload *offload;
 	bool ret;
 
-	if (!bpf_prog_is_dev_bound(prog->aux) || !bpf_map_is_dev_bound(map))
+	if (!bpf_prog_is_dev_bound(prog->aux))
 		return false;
+	if (!bpf_map_is_dev_bound(map))
+		return bpf_map_offload_neutral(map);
 
 	down_read(&bpf_devs_lock);
 	offload = prog->aux->offload;