[PATCH bpf-next v2 0/3] bpf: Introduce BPF_F_CPU flag for percpu_array maps

[PATCH bpf-next v2 0/3] bpf: Introduce BPF_F_CPU flag for percpu_array maps

[Leon Hwang]

This patch set introduces the BPF_F_CPU flag for percpu_array maps, as
discussed in the thread of
"[PATCH bpf-next v3 0/4] bpf: Introduce global percpu data"[1].

The goal is to reduce data caching overhead in light skeletons by allowing
a single value to be reused across all CPUs. This avoids the M:N problem
where M cached values are used to update a map on N CPUs kernel.

The BPF_F_CPU flag is accompanied by *flags*-embedded cpu info, which
specifies the target CPUs for the operation:

* For lookup operations: the flag field alongside cpu info enable querying
  a value on the specified CPU.
* For update operations:
  * If cpu == (u32)~0, the provided value is copied to all CPUs.
  * Otherwise, the value is copied to the specified CPU only.

Currently, this functionality is only supported for percpu_array maps.

Links:
[1] https://lore.kernel.org/bpf/20250526162146.24429-1-leon.hwang@linux.dev/

Changes:
v1 -> v2:
* Address comments from Andrii:
  * Embed cpu info as high 32 bits of *flags* totally.
  * Use ERANGE instead of E2BIG.
  * Few format issues.

RFC v2 -> v1:
* Address comments from Andrii:
  * Use '&=' and '|='.
  * Replace 'reuse_value' with simpler and less duplication code.
  * Replace 'ASSERT_FALSE' with two 'ASSERT_OK_PTR's in self test.

RFC v1 -> RFC v2:
* Address comments from Andrii:
  * Embed cpu to flags on kernel side.
  * Change BPF_ALL_CPU macro to BPF_ALL_CPUS enum.
  * Copy/update element within RCU protection.
  * Update bpf_map_value_size() including BPF_F_CPU case.
  * Use zero as default value to get cpu option.
  * Update documents of APIs to be generic.
  * Add size_t:0 to opts definitions.
  * Update validate_map_op() including BPF_F_CPU case.
  * Use LIBBPF_OPTS instead of DECLARE_LIBBPF_OPTS.

Leon Hwang (3):
  bpf: Introduce BPF_F_CPU flag for percpu_array maps
  libbpf: Support BPF_F_CPU for percpu_array maps
  selftests/bpf: Add case to test BPF_F_CPU

Leon Hwang (3):
  bpf: Introduce BPF_F_CPU flag for percpu_array maps
  libbpf: Support BPF_F_CPU for percpu_array maps
  selftests/bpf: Add case to test BPF_F_CPU

 include/linux/bpf.h                           |   3 +-
 include/uapi/linux/bpf.h                      |   6 +
 kernel/bpf/arraymap.c                         |  54 +++++--
 kernel/bpf/syscall.c                          |  77 +++++----
 tools/include/uapi/linux/bpf.h                |   6 +
 tools/lib/bpf/bpf.h                           |   5 +
 tools/lib/bpf/libbpf.c                        |  28 +++-
 tools/lib/bpf/libbpf.h                        |  17 +-
 .../selftests/bpf/prog_tests/percpu_alloc.c   | 149 ++++++++++++++++++
 .../selftests/bpf/progs/percpu_array_flag.c   |  24 +++
 10 files changed, 309 insertions(+), 60 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/progs/percpu_array_flag.c

--
2.50.1

[PATCH bpf-next v2 1/3] bpf: Introduce BPF_F_CPU flag for percpu_array maps

[Leon Hwang]

Introduce support for the BPF_F_CPU flag in percpu_array maps to allow
updating values for specified CPU or for all CPUs with a single value.

This enhancement enables:

* Efficient update of all CPUs using a single value when cpu == (u32)~0.
* Targeted update or lookup for a specified CPU otherwise.

The flag is passed via:

* map_flags in bpf_percpu_array_update() along with embedded cpu field.
* elem_flags in generic_map_update_batch() along with embedded cpu field.

Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
---
 include/linux/bpf.h            |  3 +-
 include/uapi/linux/bpf.h       |  6 +++
 kernel/bpf/arraymap.c          | 54 ++++++++++++++++++------
 kernel/bpf/syscall.c           | 77 +++++++++++++++++++++-------------
 tools/include/uapi/linux/bpf.h |  6 +++
 5 files changed, 103 insertions(+), 43 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index cc700925b802f..c17c45f797ed9 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -2691,7 +2691,8 @@ 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,
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 233de8677382e..67bc35e4d6a8d 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -1372,6 +1372,12 @@ 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, /* map_update for percpu_array */
+};
+
+enum {
+	/* indicate updating value across all CPUs for percpu maps. */
+	BPF_ALL_CPUS	= (__u32)~0,
 };
 
 /* flags for BPF_MAP_CREATE command */
diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
index 3d080916faf97..98759f0b22397 100644
--- a/kernel/bpf/arraymap.c
+++ b/kernel/bpf/arraymap.c
@@ -295,17 +295,24 @@ 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;
 
+	cpu = flags >> 32;
+	flags &= (u32)~0;
+	if (unlikely(flags > BPF_F_CPU))
+		return -EINVAL;
+	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
@@ -313,10 +320,15 @@ int bpf_percpu_array_copy(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, 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;
@@ -387,13 +399,20 @@ int bpf_percpu_array_update(struct bpf_map *map, void *key, void *value,
 	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(map_flags > BPF_EXIST))
+	cpu = map_flags >> 32;
+	map_flags &= (u32)~0;
+	if (unlikely(map_flags > BPF_F_CPU))
 		/* unknown flags */
 		return -EINVAL;
 
+	if (unlikely((map_flags & BPF_F_CPU) && cpu != BPF_ALL_CPUS &&
+		     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 */
 		return -E2BIG;
@@ -411,10 +430,19 @@ 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) && cpu != BPF_ALL_CPUS) {
+		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_CPU is specified,
+			 * otherwise value is an array of per-cpu values.
+			 */
+			if (!(map_flags & BPF_F_CPU))
+				off += size;
+			bpf_obj_free_fields(array->map.record, per_cpu_ptr(pptr, cpu));
+		}
 	}
 	rcu_read_unlock();
 	return 0;
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 0fbfa8532c392..43f19d02bc5ce 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -131,8 +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 ((flags & BPF_F_CPU) && map->map_type == BPF_MAP_TYPE_PERCPU_ARRAY)
+		return round_up(map->value_size, 8);
+
 	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 ||
@@ -314,7 +317,7 @@ 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) {
@@ -1669,7 +1672,10 @@ static int map_lookup_elem(union bpf_attr *attr)
 	if (CHECK_ATTR(BPF_MAP_LOOKUP_ELEM))
 		return -EINVAL;
 
-	if (attr->flags & ~BPF_F_LOCK)
+	if ((u32)attr->flags & ~(BPF_F_LOCK | BPF_F_CPU))
+		return -EINVAL;
+
+	if (!((u32)attr->flags & BPF_F_CPU) && attr->flags >> 32)
 		return -EINVAL;
 
 	CLASS(fd, f)(attr->map_fd);
@@ -1679,7 +1685,7 @@ static int map_lookup_elem(union bpf_attr *attr)
 	if (!(map_get_sys_perms(map, f) & FMODE_CAN_READ))
 		return -EPERM;
 
-	if ((attr->flags & BPF_F_LOCK) &&
+	if (((u32)attr->flags & BPF_F_LOCK) &&
 	    !btf_record_has_field(map->record, BPF_SPIN_LOCK))
 		return -EINVAL;
 
@@ -1687,7 +1693,7 @@ 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);
@@ -1744,19 +1750,24 @@ static int map_update_elem(union bpf_attr *attr, bpfptr_t uattr)
 		goto err_put;
 	}
 
-	if ((attr->flags & BPF_F_LOCK) &&
+	if (((u32)attr->flags & BPF_F_LOCK) &&
 	    !btf_record_has_field(map->record, BPF_SPIN_LOCK)) {
 		err = -EINVAL;
 		goto err_put;
 	}
 
+	if (!((u32)attr->flags & BPF_F_CPU) && attr->flags >> 32) {
+		err = -EINVAL;
+		goto err_put;
+	}
+
 	key = ___bpf_copy_key(ukey, map->key_size);
 	if (IS_ERR(key)) {
 		err = PTR_ERR(key);
 		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);
@@ -1942,6 +1953,25 @@ int generic_map_delete_batch(struct bpf_map *map,
 	return err;
 }
 
+static int check_map_batch_elem_flags(struct bpf_map *map, u64 elem_flags)
+{
+	u32 flags = elem_flags;
+
+	if (flags & ~(BPF_F_LOCK | BPF_F_CPU))
+		return -EINVAL;
+
+	if ((flags & BPF_F_LOCK) && !btf_record_has_field(map->record, BPF_SPIN_LOCK))
+		return -EINVAL;
+
+	if (!(flags & BPF_F_CPU) && elem_flags >> 32)
+		return -EINVAL;
+
+	if ((flags & BPF_F_CPU) && map->map_type != BPF_MAP_TYPE_PERCPU_ARRAY)
+		return -EINVAL;
+
+	return 0;
+}
+
 int generic_map_update_batch(struct bpf_map *map, struct file *map_file,
 			     const union bpf_attr *attr,
 			     union bpf_attr __user *uattr)
@@ -1952,15 +1982,11 @@ int generic_map_update_batch(struct bpf_map *map, struct file *map_file,
 	void *key, *value;
 	int err = 0;
 
-	if (attr->batch.elem_flags & ~BPF_F_LOCK)
-		return -EINVAL;
-
-	if ((attr->batch.elem_flags & BPF_F_LOCK) &&
-	    !btf_record_has_field(map->record, BPF_SPIN_LOCK)) {
-		return -EINVAL;
-	}
+	err = check_map_batch_elem_flags(map, attr->batch.elem_flags);
+	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)
@@ -1986,9 +2012,7 @@ int generic_map_update_batch(struct bpf_map *map, struct file *map_file,
 		    copy_from_user(value, values + cp * value_size, value_size))
 			break;
 
-		err = bpf_map_update_value(map, map_file, key, value,
-					   attr->batch.elem_flags);
-
+		err = bpf_map_update_value(map, map_file, key, value, attr->batch.elem_flags);
 		if (err)
 			break;
 		cond_resched();
@@ -2015,14 +2039,11 @@ int generic_map_lookup_batch(struct bpf_map *map,
 	u32 value_size, cp, max_count;
 	int err;
 
-	if (attr->batch.elem_flags & ~BPF_F_LOCK)
-		return -EINVAL;
-
-	if ((attr->batch.elem_flags & BPF_F_LOCK) &&
-	    !btf_record_has_field(map->record, BPF_SPIN_LOCK))
-		return -EINVAL;
+	err = check_map_batch_elem_flags(map, attr->batch.elem_flags);
+	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)
@@ -2056,9 +2077,7 @@ int generic_map_lookup_batch(struct bpf_map *map,
 		rcu_read_unlock();
 		if (err)
 			break;
-		err = bpf_map_copy_value(map, key, value,
-					 attr->batch.elem_flags);
-
+		err = bpf_map_copy_value(map, key, value, attr->batch.elem_flags);
 		if (err == -ENOENT)
 			goto next_key;
 
@@ -2144,7 +2163,7 @@ 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);
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 233de8677382e..67bc35e4d6a8d 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -1372,6 +1372,12 @@ 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, /* map_update for percpu_array */
+};
+
+enum {
+	/* indicate updating value across all CPUs for percpu maps. */
+	BPF_ALL_CPUS	= (__u32)~0,
 };
 
 /* flags for BPF_MAP_CREATE command */
-- 
2.50.1

[PATCH bpf-next v2 2/3] libbpf: Support BPF_F_CPU for percpu_array maps

[Leon Hwang]

Add libbpf support for the BPF_F_CPU flag for percpu_array maps by
embedding the cpu info into the high 32 bits of:

1. **flags**: bpf_map_lookup_elem_flags(), bpf_map__lookup_elem(),
   bpf_map_update_elem() and bpf_map__update_elem()
2. **opts->elem_flags**: bpf_map_lookup_batch() and
   bpf_map_update_batch()

Behavior:

* If cpu is (u32)~0, the update is applied across all CPUs.
* Otherwise, it updates value only to the specified CPU.
* If cpu is (u32)~0, lookup values across all CPUs.
* Otherwise, it lookups value only from the specified CPU.

Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
---
 tools/lib/bpf/bpf.h    |  5 +++++
 tools/lib/bpf/libbpf.c | 28 ++++++++++++++++++++++------
 tools/lib/bpf/libbpf.h | 17 ++++++-----------
 3 files changed, 33 insertions(+), 17 deletions(-)

diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
index 7252150e7ad35..8dea8216d5992 100644
--- a/tools/lib/bpf/bpf.h
+++ b/tools/lib/bpf/bpf.h
@@ -286,6 +286,11 @@ LIBBPF_API int bpf_map_lookup_and_delete_batch(int fd, void *in_batch,
  *    Update spin_lock-ed map elements. This must be
  *    specified if the map value contains a spinlock.
  *
+ * **BPF_F_CPU**
+ *    As for percpu map, the cpu info is embedded into the high 32 bits of
+ *    **opts->elem_flags**. Update value across all CPUs if cpu is (__u32)~0,
+ *    or on specified CPU otherwise.
+ *
  * @param fd BPF map file descriptor
  * @param keys pointer to an array of *count* keys
  * @param values pointer to an array of *count* values
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index fb4d92c5c3394..29ada5d62ba26 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -10593,8 +10593,10 @@ bpf_object__find_map_fd_by_name(const struct bpf_object *obj, const char *name)
 }
 
 static int validate_map_op(const struct bpf_map *map, size_t key_sz,
-			   size_t value_sz, bool check_value_sz)
+			   size_t value_sz, bool check_value_sz, __u64 flags)
 {
+	__u32 cpu;
+
 	if (!map_is_created(map)) /* map is not yet created */
 		return -ENOENT;
 
@@ -10612,6 +10614,20 @@ static int validate_map_op(const struct bpf_map *map, size_t key_sz,
 	if (!check_value_sz)
 		return 0;
 
+	if (flags & BPF_F_CPU) {
+		if (map->def.type != BPF_MAP_TYPE_PERCPU_ARRAY)
+			return -EINVAL;
+		cpu = flags >> 32;
+		if (cpu != BPF_ALL_CPUS && cpu >= libbpf_num_possible_cpus())
+			return -ERANGE;
+		if (map->def.value_size != value_sz) {
+			pr_warn("map '%s': unexpected value size %zu provided, expected %u\n",
+				map->name, value_sz, map->def.value_size);
+			return -EINVAL;
+		}
+		return 0;
+	}
+
 	switch (map->def.type) {
 	case BPF_MAP_TYPE_PERCPU_ARRAY:
 	case BPF_MAP_TYPE_PERCPU_HASH:
@@ -10644,7 +10660,7 @@ int bpf_map__lookup_elem(const struct bpf_map *map,
 {
 	int err;
 
-	err = validate_map_op(map, key_sz, value_sz, true);
+	err = validate_map_op(map, key_sz, value_sz, true, flags);
 	if (err)
 		return libbpf_err(err);
 
@@ -10657,7 +10673,7 @@ int bpf_map__update_elem(const struct bpf_map *map,
 {
 	int err;
 
-	err = validate_map_op(map, key_sz, value_sz, true);
+	err = validate_map_op(map, key_sz, value_sz, true, flags);
 	if (err)
 		return libbpf_err(err);
 
@@ -10669,7 +10685,7 @@ int bpf_map__delete_elem(const struct bpf_map *map,
 {
 	int err;
 
-	err = validate_map_op(map, key_sz, 0, false /* check_value_sz */);
+	err = validate_map_op(map, key_sz, 0, false /* check_value_sz */, 0);
 	if (err)
 		return libbpf_err(err);
 
@@ -10682,7 +10698,7 @@ int bpf_map__lookup_and_delete_elem(const struct bpf_map *map,
 {
 	int err;
 
-	err = validate_map_op(map, key_sz, value_sz, true);
+	err = validate_map_op(map, key_sz, value_sz, true, 0);
 	if (err)
 		return libbpf_err(err);
 
@@ -10694,7 +10710,7 @@ int bpf_map__get_next_key(const struct bpf_map *map,
 {
 	int err;
 
-	err = validate_map_op(map, key_sz, 0, false /* check_value_sz */);
+	err = validate_map_op(map, key_sz, 0, false /* check_value_sz */, 0);
 	if (err)
 		return libbpf_err(err);
 
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index d1cf813a057bc..bde22b017a3ce 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -1169,10 +1169,11 @@ LIBBPF_API struct bpf_map *bpf_map__inner_map(struct bpf_map *map);
  * @param key_sz size in bytes of key data, needs to match BPF map definition's **key_size**
  * @param value pointer to memory in which looked up value will be stored
  * @param value_sz size in byte of value data memory; it has to match BPF map
- * definition's **value_size**. For per-CPU BPF maps value size has to be
- * a product of BPF map value size and number of possible CPUs in the system
- * (could be fetched with **libbpf_num_possible_cpus()**). Note also that for
- * per-CPU values value size has to be aligned up to closest 8 bytes for
+ * definition's **value_size**. For per-CPU BPF maps, value size can be
+ * definition's **value_size** if **BPF_F_CPU** is specified in **flags**,
+ * otherwise a product of BPF map value size and number of possible CPUs in the
+ * system (could be fetched with **libbpf_num_possible_cpus()**). Note else that
+ * for per-CPU values value size has to be aligned up to closest 8 bytes for
  * alignment reasons, so expected size is: `round_up(value_size, 8)
  * * libbpf_num_possible_cpus()`.
  * @flags extra flags passed to kernel for this operation
@@ -1192,13 +1193,7 @@ LIBBPF_API int bpf_map__lookup_elem(const struct bpf_map *map,
  * @param key pointer to memory containing bytes of the key
  * @param key_sz size in bytes of key data, needs to match BPF map definition's **key_size**
  * @param value pointer to memory containing bytes of the value
- * @param value_sz size in byte of value data memory; it has to match BPF map
- * definition's **value_size**. For per-CPU BPF maps value size has to be
- * a product of BPF map value size and number of possible CPUs in the system
- * (could be fetched with **libbpf_num_possible_cpus()**). Note also that for
- * per-CPU values value size has to be aligned up to closest 8 bytes for
- * alignment reasons, so expected size is: `round_up(value_size, 8)
- * * libbpf_num_possible_cpus()`.
+ * @param value_sz refer to **bpf_map__lookup_elem**'s description.'
  * @flags extra flags passed to kernel for this operation
  * @return 0, on success; negative error, otherwise
  *
-- 
2.50.1

[PATCH bpf-next v2 3/3] selftests/bpf: Add case to test BPF_F_CPU

[Leon Hwang]

This patch adds test coverage for the new BPF_F_CPU flag support in
percpu_array maps. The following APIs are exercised:

* bpf_map_update_batch()
* bpf_map_lookup_batch()
* bpf_map_update_elem()
* bpf_map__update_elem()
* bpf_map_lookup_elem_flags()
* bpf_map__lookup_elem()

cd tools/testing/selftests/bpf/
./test_progs -t percpu_alloc
253/13  percpu_alloc/cpu_flag_tests:OK
253     percpu_alloc:OK
Summary: 1/13 PASSED, 0 SKIPPED, 0 FAILED

Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
---
 .../selftests/bpf/prog_tests/percpu_alloc.c   | 149 ++++++++++++++++++
 .../selftests/bpf/progs/percpu_array_flag.c   |  24 +++
 2 files changed, 173 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/progs/percpu_array_flag.c

diff --git a/tools/testing/selftests/bpf/prog_tests/percpu_alloc.c b/tools/testing/selftests/bpf/prog_tests/percpu_alloc.c
index 343da65864d6d..2500675d489df 100644
--- a/tools/testing/selftests/bpf/prog_tests/percpu_alloc.c
+++ b/tools/testing/selftests/bpf/prog_tests/percpu_alloc.c
@@ -3,6 +3,7 @@
 #include "percpu_alloc_array.skel.h"
 #include "percpu_alloc_cgrp_local_storage.skel.h"
 #include "percpu_alloc_fail.skel.h"
+#include "percpu_array_flag.skel.h"
 
 static void test_array(void)
 {
@@ -115,6 +116,152 @@ static void test_failure(void) {
 	RUN_TESTS(percpu_alloc_fail);
 }
 
+static void test_cpu_flag(void)
+{
+	int map_fd, *keys = NULL, value_size, cpu, i, j, nr_cpus, err;
+	size_t key_sz = sizeof(int), value_sz = sizeof(u64);
+	u64 batch = 0, *values = NULL, flags;
+	struct percpu_array_flag *skel;
+	const u64 value = 0xDEADC0DE;
+	u32 count, max_entries;
+	struct bpf_map *map;
+	LIBBPF_OPTS(bpf_map_batch_opts, batch_opts);
+
+	nr_cpus = libbpf_num_possible_cpus();
+	if (!ASSERT_GT(nr_cpus, 0, "libbpf_num_possible_cpus"))
+		return;
+
+	skel = percpu_array_flag__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "percpu_array_flag__open_and_load"))
+		return;
+
+	map = skel->maps.percpu;
+	map_fd = bpf_map__fd(map);
+	max_entries = bpf_map__max_entries(map);
+
+	value_size = value_sz * nr_cpus;
+	values = calloc(max_entries, value_size);
+	if (!ASSERT_OK_PTR(values, "calloc values"))
+		goto out;
+	keys = calloc(max_entries, key_sz);
+	if (!ASSERT_OK_PTR(keys, "calloc keys"))
+		goto out;
+
+	for (i = 0; i < max_entries; i++)
+		keys[i] = i;
+	memset(values, 0, max_entries * value_size);
+
+	batch_opts.elem_flags = (u64)nr_cpus << 32 | BPF_F_CPU;
+	err = bpf_map_update_batch(map_fd, keys, values, &max_entries, &batch_opts);
+	if (!ASSERT_EQ(err, -ERANGE, "bpf_map_update_batch -ERANGE"))
+		goto out;
+
+	for (cpu = 0; cpu < nr_cpus; cpu++) {
+		memset(values, 0, max_entries * value_size);
+
+		/* clear values across all CPUs */
+		batch_opts.elem_flags = (u64)BPF_ALL_CPUS << 32 | BPF_F_CPU;
+		err = bpf_map_update_batch(map_fd, keys, values, &max_entries, &batch_opts);
+		if (!ASSERT_OK(err, "bpf_map_update_batch all cpus"))
+			goto out;
+
+		/* update values on specified CPU */
+		for (i = 0; i < max_entries; i++)
+			values[i] = value;
+
+		batch_opts.elem_flags = (u64)cpu << 32 | BPF_F_CPU;
+		err = bpf_map_update_batch(map_fd, keys, values, &max_entries, &batch_opts);
+		if (!ASSERT_OK(err, "bpf_map_update_batch specified cpu"))
+			goto out;
+
+		/* lookup values on specified CPU */
+		memset(values, 0, max_entries * value_sz);
+		err = bpf_map_lookup_batch(map_fd, NULL, &batch, keys, values, &count, &batch_opts);
+		if (!ASSERT_TRUE(!err || err == -ENOENT, "bpf_map_lookup_batch specified cpu"))
+			goto out;
+
+		for (i = 0; i < max_entries; i++)
+			if (!ASSERT_EQ(values[i], value, "value on specified cpu"))
+				goto out;
+
+		/* lookup values from all CPUs */
+		batch_opts.elem_flags = 0;
+		memset(values, 0, max_entries * value_size);
+		err = bpf_map_lookup_batch(map_fd, NULL, &batch, keys, values, &count, &batch_opts);
+		if (!ASSERT_TRUE(!err || err == -ENOENT, "bpf_map_lookup_batch all cpus"))
+			goto out;
+
+		for (i = 0; i < max_entries; i++) {
+			for (j = 0; j < nr_cpus; j++) {
+				if (!ASSERT_EQ(values[i*nr_cpus + j], j != cpu ? 0 : value,
+					       "value on specified cpu"))
+					goto out;
+			}
+		}
+	}
+
+	flags = (u64)nr_cpus << 32 | BPF_F_CPU;
+	err = bpf_map_update_elem(map_fd, keys, values, flags);
+	if (!ASSERT_EQ(err, -ERANGE, "bpf_map_update_elem -ERANGE"))
+		goto out;
+
+	err = bpf_map__update_elem(map, keys, key_sz, values, value_sz, flags);
+	if (!ASSERT_EQ(err, -ERANGE, "bpf_map__update_elem -ERANGE"))
+		goto out;
+
+	err = bpf_map_lookup_elem_flags(map_fd, keys, values, flags);
+	if (!ASSERT_EQ(err, -ERANGE, "bpf_map_lookup_elem_flags -ERANGE"))
+		goto out;
+
+	err = bpf_map__lookup_elem(map, keys, key_sz, values, value_sz, flags);
+	if (!ASSERT_EQ(err, -ERANGE, "bpf_map__lookup_elem -ERANGE"))
+		goto out;
+
+	/* clear value on all cpus */
+	batch_opts.elem_flags = (u64)BPF_ALL_CPUS << 32 | BPF_F_CPU;
+	memset(values, 0, max_entries * value_sz);
+	err = bpf_map_update_batch(map_fd, keys, values, &max_entries, &batch_opts);
+	if (!ASSERT_OK(err, "bpf_map_update_batch all cpus"))
+		goto out;
+
+	for (cpu = 0; cpu < nr_cpus; cpu++) {
+		/* update value on specified cpu */
+		values[0] = value;
+		flags = (u64)cpu << 32 | BPF_F_CPU;
+		for (i = 0; i < max_entries; i++) {
+			err = bpf_map__update_elem(map, keys + i, key_sz, values, value_sz, flags);
+			if (!ASSERT_OK(err, "bpf_map__update_elem specified cpu"))
+				goto out;
+
+			for (j = 0; j < nr_cpus; j++) {
+				/* lookup then check value on CPUs */
+				flags = (u64)j << 32 | BPF_F_CPU;
+				err = bpf_map__lookup_elem(map, keys + i, key_sz, values, value_sz,
+							   flags);
+				if (!ASSERT_OK(err, "bpf_map__lookup_elem specified cpu"))
+					goto out;
+				if (!ASSERT_EQ(values[0], j != cpu ? 0 : value,
+					       "bpf_map__lookup_elem value on specified cpu"))
+					goto out;
+			}
+		}
+
+		/* clear value on specified cpu */
+		values[0] = 0;
+		flags = (u64)cpu << 32 | BPF_F_CPU;
+		err = bpf_map__update_elem(map, keys, key_sz, values, value_sz, flags);
+		if (!ASSERT_OK(err, "bpf_map__update_elem specified cpu"))
+			goto out;
+	}
+
+out:
+	if (keys)
+		free(keys);
+	if (values)
+		free(values);
+	percpu_array_flag__destroy(skel);
+}
+
 void test_percpu_alloc(void)
 {
 	if (test__start_subtest("array"))
@@ -125,4 +272,6 @@ void test_percpu_alloc(void)
 		test_cgrp_local_storage();
 	if (test__start_subtest("failure_tests"))
 		test_failure();
+	if (test__start_subtest("cpu_flag_tests"))
+		test_cpu_flag();
 }
diff --git a/tools/testing/selftests/bpf/progs/percpu_array_flag.c b/tools/testing/selftests/bpf/progs/percpu_array_flag.c
new file mode 100644
index 0000000000000..4d92e121958ee
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/percpu_array_flag.c
@@ -0,0 +1,24 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+struct {
+	__uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
+	__uint(max_entries, 2);
+	__type(key, int);
+	__type(value, u64);
+} percpu SEC(".maps");
+
+SEC("fentry/bpf_fentry_test1")
+int BPF_PROG(test_percpu_array, int x)
+{
+	u64 value = 0xDEADC0DE;
+	int key = 0;
+
+	bpf_map_update_elem(&percpu, &key, &value, BPF_ANY);
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";
+
-- 
2.50.1

Re: [PATCH bpf-next v2 1/3] bpf: Introduce BPF_F_CPU flag for percpu_array maps

[Jiri Olsa]

On Wed, Aug 06, 2025 at 12:30:15AM +0800, Leon Hwang wrote:
> Introduce support for the BPF_F_CPU flag in percpu_array maps to allow
> updating values for specified CPU or for all CPUs with a single value.
> 
> This enhancement enables:
> 
> * Efficient update of all CPUs using a single value when cpu == (u32)~0.
> * Targeted update or lookup for a specified CPU otherwise.
> 
> The flag is passed via:
> 
> * map_flags in bpf_percpu_array_update() along with embedded cpu field.
> * elem_flags in generic_map_update_batch() along with embedded cpu field.
> 
> Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
> ---
>  include/linux/bpf.h            |  3 +-
>  include/uapi/linux/bpf.h       |  6 +++
>  kernel/bpf/arraymap.c          | 54 ++++++++++++++++++------
>  kernel/bpf/syscall.c           | 77 +++++++++++++++++++++-------------
>  tools/include/uapi/linux/bpf.h |  6 +++
>  5 files changed, 103 insertions(+), 43 deletions(-)
> 
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index cc700925b802f..c17c45f797ed9 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -2691,7 +2691,8 @@ 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,
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 233de8677382e..67bc35e4d6a8d 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -1372,6 +1372,12 @@ 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, /* map_update for percpu_array */
> +};
> +
> +enum {
> +	/* indicate updating value across all CPUs for percpu maps. */
> +	BPF_ALL_CPUS	= (__u32)~0,
>  };
>  
>  /* flags for BPF_MAP_CREATE command */
> diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
> index 3d080916faf97..98759f0b22397 100644
> --- a/kernel/bpf/arraymap.c
> +++ b/kernel/bpf/arraymap.c
> @@ -295,17 +295,24 @@ 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;
>  
> +	cpu = flags >> 32;
> +	flags &= (u32)~0;

is this necessary?

> +	if (unlikely(flags > BPF_F_CPU))
> +		return -EINVAL;
> +	if (unlikely((flags & BPF_F_CPU) && cpu >= num_possible_cpus()))
> +		return -ERANGE;

should we check cpu != BPF_ALL_CPUS in here?

> +
>  	/* 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
> @@ -313,10 +320,15 @@ int bpf_percpu_array_copy(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, 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;
> @@ -387,13 +399,20 @@ int bpf_percpu_array_update(struct bpf_map *map, void *key, void *value,
>  	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(map_flags > BPF_EXIST))
> +	cpu = map_flags >> 32;
> +	map_flags &= (u32)~0;
> +	if (unlikely(map_flags > BPF_F_CPU))
>  		/* unknown flags */
>  		return -EINVAL;
>  
> +	if (unlikely((map_flags & BPF_F_CPU) && cpu != BPF_ALL_CPUS &&
> +		     cpu >= num_possible_cpus()))
> +		/* invalid cpu */
> +		return -ERANGE;

looks like same check as in bpf_percpu_array_copy, maybe we could add
some helper function for that?

> +
>  	if (unlikely(index >= array->map.max_entries))
>  		/* all elements were pre-allocated, cannot insert a new one */
>  		return -E2BIG;
> @@ -411,10 +430,19 @@ 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) && cpu != BPF_ALL_CPUS) {
> +		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_CPU is specified,
> +			 * otherwise value is an array of per-cpu values.
> +			 */
> +			if (!(map_flags & BPF_F_CPU))
> +				off += size;
> +			bpf_obj_free_fields(array->map.record, per_cpu_ptr(pptr, cpu));
> +		}
>  	}
>  	rcu_read_unlock();
>  	return 0;
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 0fbfa8532c392..43f19d02bc5ce 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -131,8 +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 ((flags & BPF_F_CPU) && map->map_type == BPF_MAP_TYPE_PERCPU_ARRAY)
> +		return round_up(map->value_size, 8);
> +

nit, maybe we could keep the same style like below and check the map
type first:

	if (map->map_type == BPF_MAP_TYPE_PERCPU_ARRAY && (flags & BPF_F_CPU))
		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 ||
> @@ -314,7 +317,7 @@ 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) {
> @@ -1669,7 +1672,10 @@ static int map_lookup_elem(union bpf_attr *attr)
>  	if (CHECK_ATTR(BPF_MAP_LOOKUP_ELEM))
>  		return -EINVAL;
>  
> -	if (attr->flags & ~BPF_F_LOCK)
> +	if ((u32)attr->flags & ~(BPF_F_LOCK | BPF_F_CPU))
> +		return -EINVAL;

I understand the u32 cast in here..

> +
> +	if (!((u32)attr->flags & BPF_F_CPU) && attr->flags >> 32)
>  		return -EINVAL;

.. but do we need it in here and other similar places below?

>  
>  	CLASS(fd, f)(attr->map_fd);
> @@ -1679,7 +1685,7 @@ static int map_lookup_elem(union bpf_attr *attr)
>  	if (!(map_get_sys_perms(map, f) & FMODE_CAN_READ))
>  		return -EPERM;
>  
> -	if ((attr->flags & BPF_F_LOCK) &&
> +	if (((u32)attr->flags & BPF_F_LOCK) &&
>  	    !btf_record_has_field(map->record, BPF_SPIN_LOCK))
>  		return -EINVAL;
>  
> @@ -1687,7 +1693,7 @@ 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);
> @@ -1744,19 +1750,24 @@ static int map_update_elem(union bpf_attr *attr, bpfptr_t uattr)
>  		goto err_put;
>  	}
>  
> -	if ((attr->flags & BPF_F_LOCK) &&
> +	if (((u32)attr->flags & BPF_F_LOCK) &&
>  	    !btf_record_has_field(map->record, BPF_SPIN_LOCK)) {
>  		err = -EINVAL;
>  		goto err_put;
>  	}
>  
> +	if (!((u32)attr->flags & BPF_F_CPU) && attr->flags >> 32) {
> +		err = -EINVAL;
> +		goto err_put;
> +	}
> +
>  	key = ___bpf_copy_key(ukey, map->key_size);
>  	if (IS_ERR(key)) {
>  		err = PTR_ERR(key);
>  		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);
> @@ -1942,6 +1953,25 @@ int generic_map_delete_batch(struct bpf_map *map,
>  	return err;
>  }
>  
> +static int check_map_batch_elem_flags(struct bpf_map *map, u64 elem_flags)
> +{
> +	u32 flags = elem_flags;
> +
> +	if (flags & ~(BPF_F_LOCK | BPF_F_CPU))
> +		return -EINVAL;
> +
> +	if ((flags & BPF_F_LOCK) && !btf_record_has_field(map->record, BPF_SPIN_LOCK))
> +		return -EINVAL;
> +
> +	if (!(flags & BPF_F_CPU) && elem_flags >> 32)
> +		return -EINVAL;
> +
> +	if ((flags & BPF_F_CPU) && map->map_type != BPF_MAP_TYPE_PERCPU_ARRAY)
> +		return -EINVAL;
> +
> +	return 0;
> +}

it seems like this check could be used also for non-batch functions as well?

also it might be more readable if we factor some check_flags function in
separate patch and then add BPF_F_CPU support


> +
>  int generic_map_update_batch(struct bpf_map *map, struct file *map_file,
>  			     const union bpf_attr *attr,
>  			     union bpf_attr __user *uattr)
> @@ -1952,15 +1982,11 @@ int generic_map_update_batch(struct bpf_map *map, struct file *map_file,
>  	void *key, *value;
>  	int err = 0;
>  
> -	if (attr->batch.elem_flags & ~BPF_F_LOCK)
> -		return -EINVAL;
> -
> -	if ((attr->batch.elem_flags & BPF_F_LOCK) &&
> -	    !btf_record_has_field(map->record, BPF_SPIN_LOCK)) {
> -		return -EINVAL;
> -	}
> +	err = check_map_batch_elem_flags(map, attr->batch.elem_flags);
> +	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)
> @@ -1986,9 +2012,7 @@ int generic_map_update_batch(struct bpf_map *map, struct file *map_file,
>  		    copy_from_user(value, values + cp * value_size, value_size))
>  			break;
>  
> -		err = bpf_map_update_value(map, map_file, key, value,
> -					   attr->batch.elem_flags);
> -
> +		err = bpf_map_update_value(map, map_file, key, value, attr->batch.elem_flags);

there's no change in here right? I'd keep it as it is

>  		if (err)
>  			break;
>  		cond_resched();
> @@ -2015,14 +2039,11 @@ int generic_map_lookup_batch(struct bpf_map *map,
>  	u32 value_size, cp, max_count;
>  	int err;
>  
> -	if (attr->batch.elem_flags & ~BPF_F_LOCK)
> -		return -EINVAL;
> -
> -	if ((attr->batch.elem_flags & BPF_F_LOCK) &&
> -	    !btf_record_has_field(map->record, BPF_SPIN_LOCK))
> -		return -EINVAL;
> +	err = check_map_batch_elem_flags(map, attr->batch.elem_flags);
> +	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)
> @@ -2056,9 +2077,7 @@ int generic_map_lookup_batch(struct bpf_map *map,
>  		rcu_read_unlock();
>  		if (err)
>  			break;
> -		err = bpf_map_copy_value(map, key, value,
> -					 attr->batch.elem_flags);
> -
> +		err = bpf_map_copy_value(map, key, value, attr->batch.elem_flags);

ditto


thanks,
jirka

>  		if (err == -ENOENT)
>  			goto next_key;
>  
> @@ -2144,7 +2163,7 @@ 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);
> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> index 233de8677382e..67bc35e4d6a8d 100644
> --- a/tools/include/uapi/linux/bpf.h
> +++ b/tools/include/uapi/linux/bpf.h
> @@ -1372,6 +1372,12 @@ 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, /* map_update for percpu_array */
> +};
> +
> +enum {
> +	/* indicate updating value across all CPUs for percpu maps. */
> +	BPF_ALL_CPUS	= (__u32)~0,
>  };
>  
>  /* flags for BPF_MAP_CREATE command */
> -- 
> 2.50.1
> 
> 

Re: [PATCH bpf-next v2 1/3] bpf: Introduce BPF_F_CPU flag for percpu_array maps

[Leon Hwang]

On Thu Aug 7, 2025 at 4:34 PM +08, Jiri Olsa wrote:
> On Wed, Aug 06, 2025 at 12:30:15AM +0800, Leon Hwang wrote:
>> Introduce support for the BPF_F_CPU flag in percpu_array maps to allow
>> updating values for specified CPU or for all CPUs with a single value.
>>

[...]

>> diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
>> index 3d080916faf97..98759f0b22397 100644
>> --- a/kernel/bpf/arraymap.c
>> +++ b/kernel/bpf/arraymap.c
>> @@ -295,17 +295,24 @@ 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;
>>
>> +	cpu = flags >> 32;
>> +	flags &= (u32)~0;
>
> is this necessary?
>

It is unnecessary.

I'll remove it and update

    if (unlikely((u32)flags > BPF_F_CPU))
        return -EINVAL;

>> +	if (unlikely(flags > BPF_F_CPU))
>> +		return -EINVAL;
>> +	if (unlikely((flags & BPF_F_CPU) && cpu >= num_possible_cpus()))
>> +		return -ERANGE;
>
> should we check cpu != BPF_ALL_CPUS in here?
>

No. It is meaningless to support cpu == BPF_ALL_CPUS, because
(flags & BPF_F_CPU) && cpu == BPF_ALL_CPUS is same as ~BPF_F_CPU.

>> +
>>  	/* 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
>> @@ -313,10 +320,15 @@ int bpf_percpu_array_copy(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, 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;
>> @@ -387,13 +399,20 @@ int bpf_percpu_array_update(struct bpf_map *map, void *key, void *value,
>>  	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(map_flags > BPF_EXIST))
>> +	cpu = map_flags >> 32;
>> +	map_flags &= (u32)~0;
>> +	if (unlikely(map_flags > BPF_F_CPU))
>>  		/* unknown flags */
>>  		return -EINVAL;
>>
>> +	if (unlikely((map_flags & BPF_F_CPU) && cpu != BPF_ALL_CPUS &&
>> +		     cpu >= num_possible_cpus()))
>> +		/* invalid cpu */
>> +		return -ERANGE;
>
> looks like same check as in bpf_percpu_array_copy, maybe we could add
> some helper function for that?
>

If they are same, I'd like to add a helper function.

>> +
>>  	if (unlikely(index >= array->map.max_entries))
>>  		/* all elements were pre-allocated, cannot insert a new one */
>>  		return -E2BIG;
>> @@ -411,10 +430,19 @@ 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) && cpu != BPF_ALL_CPUS) {
>> +		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_CPU is specified,
>> +			 * otherwise value is an array of per-cpu values.
>> +			 */
>> +			if (!(map_flags & BPF_F_CPU))
>> +				off += size;
>> +			bpf_obj_free_fields(array->map.record, per_cpu_ptr(pptr, cpu));
>> +		}
>>  	}
>>  	rcu_read_unlock();
>>  	return 0;
>> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
>> index 0fbfa8532c392..43f19d02bc5ce 100644
>> --- a/kernel/bpf/syscall.c
>> +++ b/kernel/bpf/syscall.c
>> @@ -131,8 +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 ((flags & BPF_F_CPU) && map->map_type == BPF_MAP_TYPE_PERCPU_ARRAY)
>> +		return round_up(map->value_size, 8);
>> +
>
> nit, maybe we could keep the same style like below and check the map
> type first:
>
> 	if (map->map_type == BPF_MAP_TYPE_PERCPU_ARRAY && (flags & BPF_F_CPU))
> 		return round_up(map->value_size, 8);
> 	else if (map->map_type == BPF_MAP_TYPE_PERCPU_HASH ||
>

Ack.

>>  	    map->map_type == BPF_MAP_TYPE_LRU_PERCPU_HASH ||
>>  	    map->map_type == BPF_MAP_TYPE_PERCPU_ARRAY ||
>> @@ -314,7 +317,7 @@ 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) {
>> @@ -1669,7 +1672,10 @@ static int map_lookup_elem(union bpf_attr *attr)
>>  	if (CHECK_ATTR(BPF_MAP_LOOKUP_ELEM))
>>  		return -EINVAL;
>>
>> -	if (attr->flags & ~BPF_F_LOCK)
>> +	if ((u32)attr->flags & ~(BPF_F_LOCK | BPF_F_CPU))
>> +		return -EINVAL;
>
> I understand the u32 cast in here..
>
>> +
>> +	if (!((u32)attr->flags & BPF_F_CPU) && attr->flags >> 32)
>>  		return -EINVAL;
>
> .. but do we need it in here and other similar places below?
>

You are right. They are unnecessary.

I will remove them in next revision.

>>
>>  	CLASS(fd, f)(attr->map_fd);
>> @@ -1679,7 +1685,7 @@ static int map_lookup_elem(union bpf_attr *attr)
>>  	if (!(map_get_sys_perms(map, f) & FMODE_CAN_READ))
>>  		return -EPERM;
>>
>> -	if ((attr->flags & BPF_F_LOCK) &&
>> +	if (((u32)attr->flags & BPF_F_LOCK) &&
>>  	    !btf_record_has_field(map->record, BPF_SPIN_LOCK))
>>  		return -EINVAL;
>>
>> @@ -1687,7 +1693,7 @@ 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);
>> @@ -1744,19 +1750,24 @@ static int map_update_elem(union bpf_attr *attr, bpfptr_t uattr)
>>  		goto err_put;
>>  	}
>>
>> -	if ((attr->flags & BPF_F_LOCK) &&
>> +	if (((u32)attr->flags & BPF_F_LOCK) &&
>>  	    !btf_record_has_field(map->record, BPF_SPIN_LOCK)) {
>>  		err = -EINVAL;
>>  		goto err_put;
>>  	}
>>
>> +	if (!((u32)attr->flags & BPF_F_CPU) && attr->flags >> 32) {
>> +		err = -EINVAL;
>> +		goto err_put;
>> +	}
>> +
>>  	key = ___bpf_copy_key(ukey, map->key_size);
>>  	if (IS_ERR(key)) {
>>  		err = PTR_ERR(key);
>>  		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);
>> @@ -1942,6 +1953,25 @@ int generic_map_delete_batch(struct bpf_map *map,
>>  	return err;
>>  }
>>
>> +static int check_map_batch_elem_flags(struct bpf_map *map, u64 elem_flags)
>> +{
>> +	u32 flags = elem_flags;
>> +
>> +	if (flags & ~(BPF_F_LOCK | BPF_F_CPU))
>> +		return -EINVAL;
>> +
>> +	if ((flags & BPF_F_LOCK) && !btf_record_has_field(map->record, BPF_SPIN_LOCK))
>> +		return -EINVAL;
>> +
>> +	if (!(flags & BPF_F_CPU) && elem_flags >> 32)
>> +		return -EINVAL;
>> +
>> +	if ((flags & BPF_F_CPU) && map->map_type != BPF_MAP_TYPE_PERCPU_ARRAY)
>> +		return -EINVAL;
>> +
>> +	return 0;
>> +}
>
> it seems like this check could be used also for non-batch functions as well?
>
> also it might be more readable if we factor some check_flags function in
> separate patch and then add BPF_F_CPU support
>

Sure. After doing a poc of adding check_flags helper function, this
check can be used also for non-batch functions.

>
>> +
>>  int generic_map_update_batch(struct bpf_map *map, struct file *map_file,
>>  			     const union bpf_attr *attr,
>>  			     union bpf_attr __user *uattr)
>> @@ -1952,15 +1982,11 @@ int generic_map_update_batch(struct bpf_map *map, struct file *map_file,
>>  	void *key, *value;
>>  	int err = 0;
>>
>> -	if (attr->batch.elem_flags & ~BPF_F_LOCK)
>> -		return -EINVAL;
>> -
>> -	if ((attr->batch.elem_flags & BPF_F_LOCK) &&
>> -	    !btf_record_has_field(map->record, BPF_SPIN_LOCK)) {
>> -		return -EINVAL;
>> -	}
>> +	err = check_map_batch_elem_flags(map, attr->batch.elem_flags);
>> +	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)
>> @@ -1986,9 +2012,7 @@ int generic_map_update_batch(struct bpf_map *map, struct file *map_file,
>>  		    copy_from_user(value, values + cp * value_size, value_size))
>>  			break;
>>
>> -		err = bpf_map_update_value(map, map_file, key, value,
>> -					   attr->batch.elem_flags);
>> -
>> +		err = bpf_map_update_value(map, map_file, key, value, attr->batch.elem_flags);
>
> there's no change in here right? I'd keep it as it is
>

Ack.

>>  		if (err)
>>  			break;
>>  		cond_resched();
>> @@ -2015,14 +2039,11 @@ int generic_map_lookup_batch(struct bpf_map *map,
>>  	u32 value_size, cp, max_count;
>>  	int err;
>>
>> -	if (attr->batch.elem_flags & ~BPF_F_LOCK)
>> -		return -EINVAL;
>> -
>> -	if ((attr->batch.elem_flags & BPF_F_LOCK) &&
>> -	    !btf_record_has_field(map->record, BPF_SPIN_LOCK))
>> -		return -EINVAL;
>> +	err = check_map_batch_elem_flags(map, attr->batch.elem_flags);
>> +	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)
>> @@ -2056,9 +2077,7 @@ int generic_map_lookup_batch(struct bpf_map *map,
>>  		rcu_read_unlock();
>>  		if (err)
>>  			break;
>> -		err = bpf_map_copy_value(map, key, value,
>> -					 attr->batch.elem_flags);
>> -
>> +		err = bpf_map_copy_value(map, key, value, attr->batch.elem_flags);
>
> ditto
>

Ack.

>
> thanks,
> jirka
>

Thanks,
Leon

[...]

Re: [PATCH bpf-next v2 1/3] bpf: Introduce BPF_F_CPU flag for percpu_array maps

[Alexei Starovoitov]

On Tue, Aug 5, 2025 at 9:30 AM Leon Hwang <leon.hwang@linux.dev> wrote:
>
> Introduce support for the BPF_F_CPU flag in percpu_array maps to allow
> updating values for specified CPU or for all CPUs with a single value.
>
> This enhancement enables:
>
> * Efficient update of all CPUs using a single value when cpu == (u32)~0.
> * Targeted update or lookup for a specified CPU otherwise.
>
> The flag is passed via:
>
> * map_flags in bpf_percpu_array_update() along with embedded cpu field.
> * elem_flags in generic_map_update_batch() along with embedded cpu field.
>
> Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
> ---
>  include/linux/bpf.h            |  3 +-
>  include/uapi/linux/bpf.h       |  6 +++
>  kernel/bpf/arraymap.c          | 54 ++++++++++++++++++------
>  kernel/bpf/syscall.c           | 77 +++++++++++++++++++++-------------
>  tools/include/uapi/linux/bpf.h |  6 +++
>  5 files changed, 103 insertions(+), 43 deletions(-)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index cc700925b802f..c17c45f797ed9 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -2691,7 +2691,8 @@ 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,
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 233de8677382e..67bc35e4d6a8d 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -1372,6 +1372,12 @@ 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, /* map_update for percpu_array */

only percpu_array?!
Aren't you doing it for percpu_hash too?

The comment should also say that upper 32-bit of flags is a cpu number.

> +};
> +
> +enum {
> +       /* indicate updating value across all CPUs for percpu maps. */
> +       BPF_ALL_CPUS    = (__u32)~0,
>  };

The name is inconsistent with BPF_F_ that was adopted long ago.

Also looking at the implementation that ~0 looks too magical.
imo it's cleaner to add another BPF_F_ALL_CPUS flag.
BPF_F_CPU = 8 and upper 32-bit select a cpu.
BPF_F_ALL_CPUS = 16 -> all cpus.

Re: [PATCH bpf-next v2 1/3] bpf: Introduce BPF_F_CPU flag for percpu_array maps

[Leon Hwang]

On Fri Aug 8, 2025 at 1:20 AM +08, Alexei Starovoitov wrote:
> On Tue, Aug 5, 2025 at 9:30 AM Leon Hwang <leon.hwang@linux.dev> wrote:
>>
>> Introduce support for the BPF_F_CPU flag in percpu_array maps to allow
>> updating values for specified CPU or for all CPUs with a single value.
>>
>> This enhancement enables:
>>
>> * Efficient update of all CPUs using a single value when cpu == (u32)~0.
>> * Targeted update or lookup for a specified CPU otherwise.
>>
>> The flag is passed via:
>>
>> * map_flags in bpf_percpu_array_update() along with embedded cpu field.
>> * elem_flags in generic_map_update_batch() along with embedded cpu field.
>>
>> Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
>> ---
>>  include/linux/bpf.h            |  3 +-
>>  include/uapi/linux/bpf.h       |  6 +++
>>  kernel/bpf/arraymap.c          | 54 ++++++++++++++++++------
>>  kernel/bpf/syscall.c           | 77 +++++++++++++++++++++-------------
>>  tools/include/uapi/linux/bpf.h |  6 +++
>>  5 files changed, 103 insertions(+), 43 deletions(-)
>>
>> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
>> index cc700925b802f..c17c45f797ed9 100644
>> --- a/include/linux/bpf.h
>> +++ b/include/linux/bpf.h
>> @@ -2691,7 +2691,8 @@ 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,
>> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
>> index 233de8677382e..67bc35e4d6a8d 100644
>> --- a/include/uapi/linux/bpf.h
>> +++ b/include/uapi/linux/bpf.h
>> @@ -1372,6 +1372,12 @@ 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, /* map_update for percpu_array */
>
> only percpu_array?!
> Aren't you doing it for percpu_hash too?
>

Only percpu_array in this patchset.

I have no need to do it for percpu_hash.

> The comment should also say that upper 32-bit of flags is a cpu number.
>
>> +};
>> +
>> +enum {
>> +       /* indicate updating value across all CPUs for percpu maps. */
>> +       BPF_ALL_CPUS    = (__u32)~0,
>>  };
>
> The name is inconsistent with BPF_F_ that was adopted long ago.
>
> Also looking at the implementation that ~0 looks too magical.
> imo it's cleaner to add another BPF_F_ALL_CPUS flag.
> BPF_F_CPU = 8 and upper 32-bit select a cpu.
> BPF_F_ALL_CPUS = 16 -> all cpus.

Sure, let us add these two flags:

       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 */

Thanks,
Leon

Re: [PATCH bpf-next v2 1/3] bpf: Introduce BPF_F_CPU flag for percpu_array maps

[Alexei Starovoitov]

On Fri, Aug 8, 2025 at 9:11 AM Leon Hwang <leon.hwang@linux.dev> wrote:
>
> On Fri Aug 8, 2025 at 1:20 AM +08, Alexei Starovoitov wrote:
> > On Tue, Aug 5, 2025 at 9:30 AM Leon Hwang <leon.hwang@linux.dev> wrote:
> >>
> >> Introduce support for the BPF_F_CPU flag in percpu_array maps to allow
> >> updating values for specified CPU or for all CPUs with a single value.
> >>
> >> This enhancement enables:
> >>
> >> * Efficient update of all CPUs using a single value when cpu == (u32)~0.
> >> * Targeted update or lookup for a specified CPU otherwise.
> >>
> >> The flag is passed via:
> >>
> >> * map_flags in bpf_percpu_array_update() along with embedded cpu field.
> >> * elem_flags in generic_map_update_batch() along with embedded cpu field.
> >>
> >> Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
> >> ---
> >>  include/linux/bpf.h            |  3 +-
> >>  include/uapi/linux/bpf.h       |  6 +++
> >>  kernel/bpf/arraymap.c          | 54 ++++++++++++++++++------
> >>  kernel/bpf/syscall.c           | 77 +++++++++++++++++++++-------------
> >>  tools/include/uapi/linux/bpf.h |  6 +++
> >>  5 files changed, 103 insertions(+), 43 deletions(-)
> >>
> >> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> >> index cc700925b802f..c17c45f797ed9 100644
> >> --- a/include/linux/bpf.h
> >> +++ b/include/linux/bpf.h
> >> @@ -2691,7 +2691,8 @@ 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,
> >> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> >> index 233de8677382e..67bc35e4d6a8d 100644
> >> --- a/include/uapi/linux/bpf.h
> >> +++ b/include/uapi/linux/bpf.h
> >> @@ -1372,6 +1372,12 @@ 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, /* map_update for percpu_array */
> >
> > only percpu_array?!
> > Aren't you doing it for percpu_hash too?
> >
>
> Only percpu_array in this patchset.
>
> I have no need to do it for percpu_hash.

You're missing the point. If we're adding the flag it should
work for all per-cpu maps. Both array and hash.

Same issue as with your other patch with common_attr.
We're not adding a feature that works for 1 out 10
commands/map types/whatever and doesn't work for the rest.
Flags/features have to be generic and consistent.

Re: [PATCH bpf-next v2 1/3] bpf: Introduce BPF_F_CPU flag for percpu_array maps

[Leon Hwang]

On Sat Aug 9, 2025 at 12:23 AM +08, Alexei Starovoitov wrote:
> On Fri, Aug 8, 2025 at 9:11 AM Leon Hwang <leon.hwang@linux.dev> wrote:
>>
>> On Fri Aug 8, 2025 at 1:20 AM +08, Alexei Starovoitov wrote:
>> > On Tue, Aug 5, 2025 at 9:30 AM Leon Hwang <leon.hwang@linux.dev> wrote:
>> >>

[...]

>> >> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
>> >> index 233de8677382e..67bc35e4d6a8d 100644
>> >> --- a/include/uapi/linux/bpf.h
>> >> +++ b/include/uapi/linux/bpf.h
>> >> @@ -1372,6 +1372,12 @@ 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, /* map_update for percpu_array */
>> >
>> > only percpu_array?!
>> > Aren't you doing it for percpu_hash too?
>> >
>>
>> Only percpu_array in this patchset.
>>
>> I have no need to do it for percpu_hash.
>
> You're missing the point. If we're adding the flag it should
> work for all per-cpu maps. Both array and hash.
>
> Same issue as with your other patch with common_attr.
> We're not adding a feature that works for 1 out 10
> commands/map types/whatever and doesn't work for the rest.
> Flags/features have to be generic and consistent.

Get it. I'll do it for other percpu maps in next revision.

Thanks,
Leon