bpf: Introduce BPF_F_CPU flag for percpu_array maps

Introduce support for the BPF_F_ALL_CPUS flag in percpu_array maps to
allow updating values for all CPUs with a single value.

Introduce support for the BPF_F_CPU flag in percpu_array maps to allow
updating value for specified CPU.

This enhancement enables:

* Efficient update values across all CPUs with a single value when
  BPF_F_ALL_CPUS is set for update_elem and update_batch APIs.
* Targeted update or lookup for a specified CPU when BPF_F_CPU is set.

The BPF_F_CPU flag is passed via:

* map_flags of lookup_elem and update_elem APIs along with embedded cpu
  field.
* elem_flags of lookup_batch and update_batch APIs along with embedded
  cpu field.

Signed-off-by: Leon Hwang <[email protected]>

Author: Asphaltt

include/linux/bpf.h

@@ -2697,7 +2697,8 @@ int map_set_for_each_callback_args(struct bpf_verifier_env *env,
 				   struct bpf_func_state *callee);
 
 int bpf_percpu_hash_copy(struct bpf_map *map, void *key, void *value);
-int bpf_percpu_array_copy(struct bpf_map *map, void *key, void *value);
+int bpf_percpu_array_copy(struct bpf_map *map, void *key, void *value,
+			  u64 flags);
 int bpf_percpu_hash_update(struct bpf_map *map, void *key, void *value,
 			   u64 flags);
 int bpf_percpu_array_update(struct bpf_map *map, void *key, void *value,

include/uapi/linux/bpf.h

@@ -1372,6 +1372,8 @@ enum {
 	BPF_NOEXIST	= 1, /* create new element if it didn't exist */
 	BPF_EXIST	= 2, /* update existing element */
 	BPF_F_LOCK	= 4, /* spin_lock-ed map_lookup/map_update */
+	BPF_F_CPU	= 8, /* cpu flag for percpu maps, upper 32-bit of flags is a cpu number */
+	BPF_F_ALL_CPUS	= 16, /* update value across all CPUs for percpu maps */
 };
 
 /* flags for BPF_MAP_CREATE command */

kernel/bpf/arraymap.c

@@ -295,28 +295,40 @@ static void *percpu_array_map_lookup_percpu_elem(struct bpf_map *map, void *key,
 	return per_cpu_ptr(array->pptrs[index & array->index_mask], cpu);
 }
 
-int bpf_percpu_array_copy(struct bpf_map *map, void *key, void *value)
+int bpf_percpu_array_copy(struct bpf_map *map, void *key, void *value, u64 flags)
 {
 	struct bpf_array *array = container_of(map, struct bpf_array, map);
 	u32 index = *(u32 *)key;
 	void __percpu *pptr;
-	int cpu, off = 0;
-	u32 size;
+	u32 size, cpu;
+	int off = 0;
 
 	if (unlikely(index >= array->map.max_entries))
 		return -ENOENT;
 
+	if (unlikely((u32)flags & ~BPF_F_CPU))
+		return -EINVAL;
+
+	cpu = flags >> 32;
+	if (unlikely((flags & BPF_F_CPU) && cpu >= num_possible_cpus()))
+		return -ERANGE;
+
 	/* per_cpu areas are zero-filled and bpf programs can only
 	 * access 'value_size' of them, so copying rounded areas
 	 * will not leak any kernel data
 	 */
 	size = array->elem_size;
 	rcu_read_lock();
 	pptr = array->pptrs[index & array->index_mask];
-	for_each_possible_cpu(cpu) {
-		copy_map_value_long(map, value + off, per_cpu_ptr(pptr, cpu));
-		check_and_init_map_value(map, value + off);
-		off += size;
+	if (flags & BPF_F_CPU) {
+		copy_map_value_long(map, value, per_cpu_ptr(pptr, cpu));
+		check_and_init_map_value(map, value);
+	} else {
+		for_each_possible_cpu(cpu) {
+			copy_map_value_long(map, value + off, per_cpu_ptr(pptr, cpu));
+			check_and_init_map_value(map, value + off);
+			off += size;
+		}
 	}
 	rcu_read_unlock();
 	return 0;
@@ -385,14 +397,22 @@ int bpf_percpu_array_update(struct bpf_map *map, void *key, void *value,
 			    u64 map_flags)
 {
 	struct bpf_array *array = container_of(map, struct bpf_array, map);
+	const u64 cpu_flags = BPF_F_CPU | BPF_F_ALL_CPUS;
 	u32 index = *(u32 *)key;
 	void __percpu *pptr;
-	int cpu, off = 0;
-	u32 size;
+	u32 size, cpu;
+	int off = 0;
 
-	if (unlikely(map_flags > BPF_EXIST))
+	if (unlikely((u32)map_flags > BPF_F_ALL_CPUS))
 		/* unknown flags */
 		return -EINVAL;
+	if (unlikely((map_flags & cpu_flags) == cpu_flags))
+		return -EINVAL;
+
+	cpu = map_flags >> 32;
+	if (unlikely((map_flags & BPF_F_CPU) && cpu >= num_possible_cpus()))
+		/* invalid cpu */
+		return -ERANGE;
 
 	if (unlikely(index >= array->map.max_entries))
 		/* all elements were pre-allocated, cannot insert a new one */
@@ -411,10 +431,20 @@ int bpf_percpu_array_update(struct bpf_map *map, void *key, void *value,
 	size = array->elem_size;
 	rcu_read_lock();
 	pptr = array->pptrs[index & array->index_mask];
-	for_each_possible_cpu(cpu) {
-		copy_map_value_long(map, per_cpu_ptr(pptr, cpu), value + off);
+	if (map_flags & BPF_F_CPU) {
+		copy_map_value_long(map, per_cpu_ptr(pptr, cpu), value);
 		bpf_obj_free_fields(array->map.record, per_cpu_ptr(pptr, cpu));
-		off += size;
+	} else {
+		for_each_possible_cpu(cpu) {
+			copy_map_value_long(map, per_cpu_ptr(pptr, cpu), value + off);
+			/* same user-provided value is used if
+			 * BPF_F_ALL_CPUS is specified, otherwise value is
+			 * an array of per-cpu values.
+			 */
+			if (!(map_flags & BPF_F_ALL_CPUS))
+				off += size;
+			bpf_obj_free_fields(array->map.record, per_cpu_ptr(pptr, cpu));
+		}
 	}
 	rcu_read_unlock();
 	return 0;

kernel/bpf/syscall.c

@@ -131,9 +131,11 @@ bool bpf_map_write_active(const struct bpf_map *map)
 	return atomic64_read(&map->writecnt) != 0;
 }
 
-static u32 bpf_map_value_size(const struct bpf_map *map)
+static u32 bpf_map_value_size(const struct bpf_map *map, u64 flags)
 {
-	if (map->map_type == BPF_MAP_TYPE_PERCPU_HASH ||
+	if (map->map_type == BPF_MAP_TYPE_PERCPU_ARRAY && (flags & (BPF_F_CPU | BPF_F_ALL_CPUS)))
+		return round_up(map->value_size, 8);
+	else if (map->map_type == BPF_MAP_TYPE_PERCPU_HASH ||
 	    map->map_type == BPF_MAP_TYPE_LRU_PERCPU_HASH ||
 	    map->map_type == BPF_MAP_TYPE_PERCPU_ARRAY ||
 	    map->map_type == BPF_MAP_TYPE_PERCPU_CGROUP_STORAGE)
@@ -314,7 +316,7 @@ static int bpf_map_copy_value(struct bpf_map *map, void *key, void *value,
 	    map->map_type == BPF_MAP_TYPE_LRU_PERCPU_HASH) {
 		err = bpf_percpu_hash_copy(map, key, value);
 	} else if (map->map_type == BPF_MAP_TYPE_PERCPU_ARRAY) {
-		err = bpf_percpu_array_copy(map, key, value);
+		err = bpf_percpu_array_copy(map, key, value, flags);
 	} else if (map->map_type == BPF_MAP_TYPE_PERCPU_CGROUP_STORAGE) {
 		err = bpf_percpu_cgroup_storage_copy(map, key, value);
 	} else if (map->map_type == BPF_MAP_TYPE_STACK_TRACE) {
@@ -1656,12 +1658,19 @@ static void *___bpf_copy_key(bpfptr_t ukey, u64 key_size)
 
 static int check_map_flags(struct bpf_map *map, u64 flags, bool check_flag)
 {
-	if (check_flag && (flags & ~BPF_F_LOCK))
+	if (check_flag && ((u32)flags & ~(BPF_F_LOCK | BPF_F_CPU | BPF_F_ALL_CPUS)))
 		return -EINVAL;
 
 	if ((flags & BPF_F_LOCK) && !btf_record_has_field(map->record, BPF_SPIN_LOCK))
 		return -EINVAL;
 
+	if (!(flags & BPF_F_CPU) && flags >> 32)
+		return -EINVAL;
+
+	if ((flags & (BPF_F_CPU | BPF_F_ALL_CPUS)) &&
+		map->map_type != BPF_MAP_TYPE_PERCPU_ARRAY)
+		return -EINVAL;
+
 	return 0;
 }
 
@@ -1695,7 +1704,7 @@ static int map_lookup_elem(union bpf_attr *attr)
 	if (IS_ERR(key))
 		return PTR_ERR(key);
 
-	value_size = bpf_map_value_size(map);
+	value_size = bpf_map_value_size(map, attr->flags);
 
 	err = -ENOMEM;
 	value = kvmalloc(value_size, GFP_USER | __GFP_NOWARN);
@@ -1762,7 +1771,7 @@ static int map_update_elem(union bpf_attr *attr, bpfptr_t uattr)
 		goto err_put;
 	}
 
-	value_size = bpf_map_value_size(map);
+	value_size = bpf_map_value_size(map, attr->flags);
 	value = kvmemdup_bpfptr(uvalue, value_size);
 	if (IS_ERR(value)) {
 		err = PTR_ERR(value);
@@ -1962,7 +1971,7 @@ int generic_map_update_batch(struct bpf_map *map, struct file *map_file,
 	if (err)
 		return err;
 
-	value_size = bpf_map_value_size(map);
+	value_size = bpf_map_value_size(map, attr->batch.elem_flags);
 
 	max_count = attr->batch.count;
 	if (!max_count)
@@ -2021,7 +2030,7 @@ int generic_map_lookup_batch(struct bpf_map *map,
 	if (err)
 		return err;
 
-	value_size = bpf_map_value_size(map);
+	value_size = bpf_map_value_size(map, attr->batch.elem_flags);
 
 	max_count = attr->batch.count;
 	if (!max_count)
@@ -2143,7 +2152,7 @@ static int map_lookup_and_delete_elem(union bpf_attr *attr)
 		goto err_put;
 	}
 
-	value_size = bpf_map_value_size(map);
+	value_size = bpf_map_value_size(map, 0);
 
 	err = -ENOMEM;
 	value = kvmalloc(value_size, GFP_USER | __GFP_NOWARN);

tools/include/uapi/linux/bpf.h

@@ -1372,6 +1372,8 @@ enum {
 	BPF_NOEXIST	= 1, /* create new element if it didn't exist */
 	BPF_EXIST	= 2, /* update existing element */
 	BPF_F_LOCK	= 4, /* spin_lock-ed map_lookup/map_update */
+	BPF_F_CPU	= 8, /* cpu flag for percpu maps, upper 32-bit of flags is a cpu number */
+	BPF_F_ALL_CPUS	= 16, /* update value across all CPUs for percpu maps */
 };
 
 /* flags for BPF_MAP_CREATE command */