bpf: add ability to charge bpf maps memory dynamically

This commits extends existing bpf maps memory charging API
to support dynamic charging/uncharging.

This is required to account memory used by maps,
if all entries are created dynamically after
the map initialization.

Signed-off-by: Roman Gushchin <guro@fb.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

include/linux/bpf.h

@@ -435,6 +435,8 @@ struct bpf_map * __must_check bpf_map_inc(struct bpf_map *map, bool uref);
 void bpf_map_put_with_uref(struct bpf_map *map);
 void bpf_map_put(struct bpf_map *map);
 int bpf_map_precharge_memlock(u32 pages);
+int bpf_map_charge_memlock(struct bpf_map *map, u32 pages);
+void bpf_map_uncharge_memlock(struct bpf_map *map, u32 pages);
 void *bpf_map_area_alloc(size_t size, int numa_node);
 void bpf_map_area_free(void *base);
 void bpf_map_init_from_attr(struct bpf_map *map, union bpf_attr *attr);

kernel/bpf/syscall.c

@@ -181,32 +181,60 @@ int bpf_map_precharge_memlock(u32 pages)
 	return 0;
 }
 
-static int bpf_map_charge_memlock(struct bpf_map *map)
+static int bpf_charge_memlock(struct user_struct *user, u32 pages)
 {
-	struct user_struct *user = get_current_user();
-	unsigned long memlock_limit;
+	unsigned long memlock_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
 
-	memlock_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
-
-	atomic_long_add(map->pages, &user->locked_vm);
-
-	if (atomic_long_read(&user->locked_vm) > memlock_limit) {
-		atomic_long_sub(map->pages, &user->locked_vm);
-		free_uid(user);
+	if (atomic_long_add_return(pages, &user->locked_vm) > memlock_limit) {
+		atomic_long_sub(pages, &user->locked_vm);
 		return -EPERM;
 	}
-	map->user = user;
 	return 0;
 }
 
-static void bpf_map_uncharge_memlock(struct bpf_map *map)
+static void bpf_uncharge_memlock(struct user_struct *user, u32 pages)
+{
+	atomic_long_sub(pages, &user->locked_vm);
+}
+
+static int bpf_map_init_memlock(struct bpf_map *map)
+{
+	struct user_struct *user = get_current_user();
+	int ret;
+
+	ret = bpf_charge_memlock(user, map->pages);
+	if (ret) {
+		free_uid(user);
+		return ret;
+	}
+	map->user = user;
+	return ret;
+}
+
+static void bpf_map_release_memlock(struct bpf_map *map)
 {
 	struct user_struct *user = map->user;
-
-	atomic_long_sub(map->pages, &user->locked_vm);
+	bpf_uncharge_memlock(user, map->pages);
 	free_uid(user);
 }
 
+int bpf_map_charge_memlock(struct bpf_map *map, u32 pages)
+{
+	int ret;
+
+	ret = bpf_charge_memlock(map->user, pages);
+	if (ret)
+		return ret;
+	map->pages += pages;
+	return ret;
+}
+
+void bpf_map_uncharge_memlock(struct bpf_map *map, u32 pages)
+{
+	bpf_uncharge_memlock(map->user, pages);
+	map->pages -= pages;
+}
+
 static int bpf_map_alloc_id(struct bpf_map *map)
 {
 	int id;
@@ -256,7 +284,7 @@ static void bpf_map_free_deferred(struct work_struct *work)
 {
 	struct bpf_map *map = container_of(work, struct bpf_map, work);
 
-	bpf_map_uncharge_memlock(map);
+	bpf_map_release_memlock(map);
 	security_bpf_map_free(map);
 	/* implementation dependent freeing */
 	map->ops->map_free(map);
@@ -492,7 +520,7 @@ static int map_create(union bpf_attr *attr)
 	if (err)
 		goto free_map_nouncharge;
 
-	err = bpf_map_charge_memlock(map);
+	err = bpf_map_init_memlock(map);
 	if (err)
 		goto free_map_sec;
 
@@ -515,7 +543,7 @@ static int map_create(union bpf_attr *attr)
 	return err;
 
 free_map:
-	bpf_map_uncharge_memlock(map);
+	bpf_map_release_memlock(map);
 free_map_sec:
 	security_bpf_map_free(map);
 free_map_nouncharge: