bpf/arena: Add bpf_arena_map_kern_vm_start() and bpf_prog_arena()

struct bpf_arena is opaque to callers outside arena.c. Add two helpers
for struct_ops subsystems that need to reach into an arena:

  bpf_arena_map_kern_vm_start(struct bpf_map *map)
    returns @map's kern_vm_start. A sched_ext follow-up needs this
    to translate kern_va <-> uaddr.

  bpf_prog_arena(struct bpf_prog *prog)
    returns the bpf_map of the arena referenced by @prog (NULL if
    @prog references no arena). The verifier enforces at most one
    arena per program. Used by struct_ops callers that auto-discover
    an arena from a member prog and need to take a map reference.

Suggested-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>
Link: https://lore.kernel.org/r/20260522172219.1423324-6-tj@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 491cc6750504..c323b3e027fe 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -618,6 +618,8 @@ void bpf_rb_root_free(const struct btf_field *field, void *rb_root,
 		      struct bpf_spin_lock *spin_lock);
 u64 bpf_arena_get_kern_vm_start(struct bpf_arena *arena);
 u64 bpf_arena_get_user_vm_start(struct bpf_arena *arena);
+u64 bpf_arena_map_kern_vm_start(struct bpf_map *map);
+struct bpf_map *bpf_prog_arena(struct bpf_prog *prog);
 int bpf_obj_name_cpy(char *dst, const char *src, unsigned int size);
 
 struct bpf_offload_dev;