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>

include/linux/bpf.h

@@ -110,6 +110,11 @@ static inline struct bpf_offloaded_map *map_to_offmap(struct bpf_map *map)
 	return container_of(map, struct bpf_offloaded_map, map);
 }
 
+static inline bool bpf_map_offload_neutral(const struct bpf_map *map)
+{
+	return map->map_type == BPF_MAP_TYPE_PERF_EVENT_ARRAY;
+}
+
 static inline bool bpf_map_support_seq_show(const struct bpf_map *map)
 {
 	return map->ops->map_seq_show_elem && map->ops->map_check_btf;

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;