bpf: Move bpf map owner out of common struct

JIRA: https://issues.redhat.com/browse/RHEL-78204

commit fd1c98f
Author: Daniel Borkmann <[email protected]>
Date:   Thu Jul 31 01:47:31 2025 +0200

    bpf: Move bpf map owner out of common struct

    Given this is only relevant for BPF tail call maps, it is adding up space
    and penalizing other map types. We also need to extend this with further
    objects to track / compare to. Therefore, lets move this out into a separate
    structure and dynamically allocate it only for BPF tail call maps.

    Signed-off-by: Daniel Borkmann <[email protected]>
    Link: https://lore.kernel.org/r/[email protected]
    Signed-off-by: Alexei Starovoitov <[email protected]>

Signed-off-by: Jerome Marchand <[email protected]>

Author: jeromemarchand

include/linux/bpf.h

@@ -260,6 +260,18 @@ struct bpf_list_node_kern {
 	void *owner;
 } __attribute__((aligned(8)));
 
+/* 'Ownership' of program-containing map is claimed by the first program
+ * that is going to use this map or by the first program which FD is
+ * stored in the map to make sure that all callers and callees have the
+ * same prog type, JITed flag and xdp_has_frags flag.
+ */
+struct bpf_map_owner {
+	enum bpf_prog_type type;
+	bool jited;
+	bool xdp_has_frags;
+	const struct btf_type *attach_func_proto;
+};
+
 struct bpf_map {
 	const struct bpf_map_ops *ops;
 	struct bpf_map *inner_map_meta;
@@ -292,18 +304,8 @@ struct bpf_map {
 		struct rcu_head rcu;
 	};
 	atomic64_t writecnt;
-	/* 'Ownership' of program-containing map is claimed by the first program
-	 * that is going to use this map or by the first program which FD is
-	 * stored in the map to make sure that all callers and callees have the
-	 * same prog type, JITed flag and xdp_has_frags flag.
-	 */
-	struct {
-		const struct btf_type *attach_func_proto;
-		spinlock_t lock;
-		enum bpf_prog_type type;
-		bool jited;
-		bool xdp_has_frags;
-	} owner;
+	spinlock_t owner_lock;
+	struct bpf_map_owner *owner;
 	bool bypass_spec_v1;
 	bool frozen; /* write-once; write-protected by freeze_mutex */
 	bool free_after_mult_rcu_gp;
@@ -2109,6 +2111,16 @@ static inline bool bpf_map_flags_access_ok(u32 access_flags)
 	       (BPF_F_RDONLY_PROG | BPF_F_WRONLY_PROG);
 }
 
+static inline struct bpf_map_owner *bpf_map_owner_alloc(struct bpf_map *map)
+{
+	return kzalloc(sizeof(*map->owner), GFP_ATOMIC);
+}
+
+static inline void bpf_map_owner_free(struct bpf_map *map)
+{
+	kfree(map->owner);
+}
+
 struct bpf_event_entry {
 	struct perf_event *event;
 	struct file *perf_file;

kernel/bpf/core.c

@@ -2382,28 +2382,29 @@ static bool __bpf_prog_map_compatible(struct bpf_map *map,
 				      const struct bpf_prog *fp)
 {
 	enum bpf_prog_type prog_type = resolve_prog_type(fp);
-	bool ret;
 	struct bpf_prog_aux *aux = fp->aux;
+	bool ret = false;
 
 	if (fp->kprobe_override)
-		return false;
+		return ret;
 
-	spin_lock(&map->owner.lock);
-	if (!map->owner.type) {
-		/* There's no owner yet where we could check for
-		 * compatibility.
-		 */
-		map->owner.type  = prog_type;
-		map->owner.jited = fp->jited;
-		map->owner.xdp_has_frags = aux->xdp_has_frags;
-		map->owner.attach_func_proto = aux->attach_func_proto;
+	spin_lock(&map->owner_lock);
+	/* There's no owner yet where we could check for compatibility. */
+	if (!map->owner) {
+		map->owner = bpf_map_owner_alloc(map);
+		if (!map->owner)
+			goto err;
+		map->owner->type  = prog_type;
+		map->owner->jited = fp->jited;
+		map->owner->xdp_has_frags = aux->xdp_has_frags;
+		map->owner->attach_func_proto = aux->attach_func_proto;
 		ret = true;
 	} else {
-		ret = map->owner.type  == prog_type &&
-		      map->owner.jited == fp->jited &&
-		      map->owner.xdp_has_frags == aux->xdp_has_frags;
+		ret = map->owner->type  == prog_type &&
+		      map->owner->jited == fp->jited &&
+		      map->owner->xdp_has_frags == aux->xdp_has_frags;
 		if (ret &&
-		    map->owner.attach_func_proto != aux->attach_func_proto) {
+		    map->owner->attach_func_proto != aux->attach_func_proto) {
 			switch (prog_type) {
 			case BPF_PROG_TYPE_TRACING:
 			case BPF_PROG_TYPE_LSM:
@@ -2416,8 +2417,8 @@ static bool __bpf_prog_map_compatible(struct bpf_map *map,
 			}
 		}
 	}
-	spin_unlock(&map->owner.lock);
-
+err:
+	spin_unlock(&map->owner_lock);
 	return ret;
 }
 

kernel/bpf/syscall.c

@@ -904,6 +904,7 @@ static void bpf_map_free_deferred(struct work_struct *work)
 
 	security_bpf_map_free(map);
 	bpf_map_release_memcg(map);
+	bpf_map_owner_free(map);
 	bpf_map_free(map);
 }
 
@@ -998,12 +999,12 @@ static void bpf_map_show_fdinfo(struct seq_file *m, struct file *filp)
 	struct bpf_map *map = filp->private_data;
 	u32 type = 0, jited = 0;
 
-	if (map_type_contains_progs(map)) {
-		spin_lock(&map->owner.lock);
-		type  = map->owner.type;
-		jited = map->owner.jited;
-		spin_unlock(&map->owner.lock);
+	spin_lock(&map->owner_lock);
+	if (map->owner) {
+		type  = map->owner->type;
+		jited = map->owner->jited;
 	}
+	spin_unlock(&map->owner_lock);
 
 	seq_printf(m,
 		   "map_type:\t%u\n"
@@ -1513,7 +1514,7 @@ static int map_create(union bpf_attr *attr, bool kernel)
 	atomic64_set(&map->refcnt, 1);
 	atomic64_set(&map->usercnt, 1);
 	mutex_init(&map->freeze_mutex);
-	spin_lock_init(&map->owner.lock);
+	spin_lock_init(&map->owner_lock);
 
 	if (attr->btf_key_type_id || attr->btf_value_type_id ||
 	    /* Even the map's value is a kernel's struct,