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

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

[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 a cpu field, which specifies the
target CPUs for the operation:

* For lookup operations: the flag and cpu field 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:
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 map
  bpf, libbpf: Support BPF_F_CPU for percpu_array map
  selftests/bpf: Add case to test BPF_F_CPU

 include/linux/bpf.h                           |   3 +-
 include/uapi/linux/bpf.h                      |   7 +
 kernel/bpf/arraymap.c                         |  54 ++++--
 kernel/bpf/syscall.c                          |  52 ++++--
 tools/include/uapi/linux/bpf.h                |   7 +
 tools/lib/bpf/bpf.c                           |  23 +++
 tools/lib/bpf/bpf.h                           |  36 +++-
 tools/lib/bpf/libbpf.c                        |  56 +++++-
 tools/lib/bpf/libbpf.h                        |  53 +++++-
 tools/lib/bpf/libbpf.map                      |   5 +
 tools/lib/bpf/libbpf_common.h                 |  14 ++
 .../selftests/bpf/prog_tests/percpu_alloc.c   | 172 ++++++++++++++++++
 .../selftests/bpf/progs/percpu_array_flag.c   |  24 +++
 13 files changed, 459 insertions(+), 47 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/progs/percpu_array_flag.c

--
2.50.1

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

[Leon Hwang]

This patch introduces support for the BPF_F_CPU flag in percpu_array maps
to allow updating or looking up values for specified CPUs 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 separated cpu field.

Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
---
 include/linux/bpf.h            |  3 +-
 include/uapi/linux/bpf.h       |  7 +++++
 kernel/bpf/arraymap.c          | 54 ++++++++++++++++++++++++++--------
 kernel/bpf/syscall.c           | 52 ++++++++++++++++++++------------
 tools/include/uapi/linux/bpf.h |  7 +++++
 5 files changed, 90 insertions(+), 33 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index f9cd2164ed23..faee5710e913 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -2671,7 +2671,8 @@ 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 233de8677382..4cad3de6899d 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 */
@@ -1549,6 +1555,7 @@ union bpf_attr {
 		__u32		map_fd;
 		__u64		elem_flags;
 		__u64		flags;
+		__u32		cpu;
 	} batch;
 
 	struct { /* anonymous struct used by BPF_PROG_LOAD command */
diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
index 3d080916faf9..d333663cbe71 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 = (u32)(flags >> 32);
+	flags &= (u32)~0;
+	if (unlikely(flags > BPF_F_CPU))
+		return -EINVAL;
+	if (unlikely((flags & BPF_F_CPU) && cpu >= num_possible_cpus()))
+		return -E2BIG;
+
 	/* 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 = (u32)(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 -E2BIG;
+
 	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 e63039817af3..0b49610d5939 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -129,8 +129,11 @@ 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 ||
@@ -312,7 +315,7 @@ 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) {
@@ -1662,7 +1665,8 @@ 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)) ||
+		(!((u32)attr->flags & BPF_F_CPU) && attr->flags >> 32))
 		return -EINVAL;
 
 	CLASS(fd, f)(attr->map_fd);
@@ -1680,7 +1684,7 @@ 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);
@@ -1749,7 +1753,7 @@ 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);
@@ -1941,19 +1945,25 @@ int generic_map_update_batch(struct bpf_map *map, struct file *map_file,
 {
 	void __user *values = u64_to_user_ptr(attr->batch.values);
 	void __user *keys = u64_to_user_ptr(attr->batch.keys);
-	u32 value_size, cp, max_count;
+	u32 value_size, cp, max_count, cpu = attr->batch.cpu;
+	u64 elem_flags = attr->batch.elem_flags;
 	void *key, *value;
 	int err = 0;
 
-	if (attr->batch.elem_flags & ~BPF_F_LOCK)
+	if (elem_flags & ~(BPF_F_LOCK | BPF_F_CPU))
 		return -EINVAL;
 
-	if ((attr->batch.elem_flags & BPF_F_LOCK) &&
+	if ((elem_flags & BPF_F_LOCK) &&
 	    !btf_record_has_field(map->record, BPF_SPIN_LOCK)) {
 		return -EINVAL;
 	}
 
-	value_size = bpf_map_value_size(map);
+	if ((elem_flags & BPF_F_CPU) &&
+		map->map_type != BPF_MAP_TYPE_PERCPU_ARRAY)
+		return -EINVAL;
+
+	value_size = bpf_map_value_size(map, elem_flags);
+	elem_flags |= ((u64)cpu) << 32;
 
 	max_count = attr->batch.count;
 	if (!max_count)
@@ -1979,8 +1989,7 @@ 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, elem_flags);
 
 		if (err)
 			break;
@@ -2004,18 +2013,24 @@ int generic_map_lookup_batch(struct bpf_map *map,
 	void __user *ubatch = u64_to_user_ptr(attr->batch.in_batch);
 	void __user *values = u64_to_user_ptr(attr->batch.values);
 	void __user *keys = u64_to_user_ptr(attr->batch.keys);
+	u32 value_size, cp, max_count, cpu = attr->batch.cpu;
 	void *buf, *buf_prevkey, *prev_key, *key, *value;
-	u32 value_size, cp, max_count;
+	u64 elem_flags = attr->batch.elem_flags;
 	int err;
 
-	if (attr->batch.elem_flags & ~BPF_F_LOCK)
+	if (elem_flags & ~(BPF_F_LOCK | BPF_F_CPU))
 		return -EINVAL;
 
-	if ((attr->batch.elem_flags & BPF_F_LOCK) &&
+	if ((elem_flags & BPF_F_LOCK) &&
 	    !btf_record_has_field(map->record, BPF_SPIN_LOCK))
 		return -EINVAL;
 
-	value_size = bpf_map_value_size(map);
+	if ((elem_flags & BPF_F_CPU) &&
+		map->map_type != BPF_MAP_TYPE_PERCPU_ARRAY)
+		return -EINVAL;
+
+	value_size = bpf_map_value_size(map, elem_flags);
+	elem_flags |= ((u64)cpu) << 32;
 
 	max_count = attr->batch.count;
 	if (!max_count)
@@ -2049,8 +2064,7 @@ 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, elem_flags);
 
 		if (err == -ENOENT)
 			goto next_key;
@@ -2137,7 +2151,7 @@ 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, attr->flags);
 
 	err = -ENOMEM;
 	value = kvmalloc(value_size, GFP_USER | __GFP_NOWARN);
@@ -5457,7 +5471,7 @@ static int bpf_task_fd_query(const union bpf_attr *attr,
 	return err;
 }
 
-#define BPF_MAP_BATCH_LAST_FIELD batch.flags
+#define BPF_MAP_BATCH_LAST_FIELD batch.cpu
 
 #define BPF_DO_BATCH(fn, ...)			\
 	do {					\
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 233de8677382..4cad3de6899d 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 */
@@ -1549,6 +1555,7 @@ union bpf_attr {
 		__u32		map_fd;
 		__u64		elem_flags;
 		__u64		flags;
+		__u32		cpu;
 	} batch;
 
 	struct { /* anonymous struct used by BPF_PROG_LOAD command */
-- 
2.50.1

[PATCH bpf-next 2/3] bpf, libbpf: Support BPF_F_CPU for percpu_array map

[Leon Hwang]

This patch adds libbpf support for the BPF_F_CPU flag in percpu_array maps,
introducing the following APIs:

1. bpf_map_update_elem_opts(): update with struct bpf_map_update_elem_opts
2. bpf_map_lookup_elem_opts(): lookup with struct bpf_map_lookup_elem_opts
3. bpf_map__update_elem_opts(): high-level wrapper with input validation
4. bpf_map__lookup_elem_opts(): high-level wrapper with input validation

Behavior:

* If opts->cpu == (u32)~0, the update is applied to all CPUs.
* Otherwise, it applies only to the specified CPU.
* Lookup APIs retrieve values from the target CPU when BPF_F_CPU is used.

Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
---
 tools/lib/bpf/bpf.c           | 23 ++++++++++++++
 tools/lib/bpf/bpf.h           | 36 +++++++++++++++++++++-
 tools/lib/bpf/libbpf.c        | 56 +++++++++++++++++++++++++++++++----
 tools/lib/bpf/libbpf.h        | 53 ++++++++++++++++++++++++++++-----
 tools/lib/bpf/libbpf.map      |  5 ++++
 tools/lib/bpf/libbpf_common.h | 14 +++++++++
 6 files changed, 173 insertions(+), 14 deletions(-)

diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
index ab40dbf9f020..8061093d84f9 100644
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c
@@ -402,6 +402,17 @@ int bpf_map_update_elem(int fd, const void *key, const void *value,
 	return libbpf_err_errno(ret);
 }
 
+int bpf_map_update_elem_opts(int fd, const void *key, const void *value,
+			     const struct bpf_map_update_elem_opts *opts)
+{
+	__u64 flags;
+	__u32 cpu;
+
+	cpu = OPTS_GET(opts, cpu, 0);
+	flags = ((__u64) cpu) << 32 | OPTS_GET(opts, flags, 0);
+	return bpf_map_update_elem(fd, key, value, flags);
+}
+
 int bpf_map_lookup_elem(int fd, const void *key, void *value)
 {
 	const size_t attr_sz = offsetofend(union bpf_attr, flags);
@@ -433,6 +444,17 @@ int bpf_map_lookup_elem_flags(int fd, const void *key, void *value, __u64 flags)
 	return libbpf_err_errno(ret);
 }
 
+int bpf_map_lookup_elem_opts(int fd, const void *key, void *value,
+			     const struct bpf_map_lookup_elem_opts *opts)
+{
+	__u64 flags;
+	__u32 cpu;
+
+	cpu = OPTS_GET(opts, cpu, 0);
+	flags = ((__u64) cpu) << 32 | OPTS_GET(opts, flags, 0);
+	return bpf_map_lookup_elem_flags(fd, key, value, flags);
+}
+
 int bpf_map_lookup_and_delete_elem(int fd, const void *key, void *value)
 {
 	const size_t attr_sz = offsetofend(union bpf_attr, flags);
@@ -542,6 +564,7 @@ static int bpf_map_batch_common(int cmd, int fd, void  *in_batch,
 	attr.batch.count = *count;
 	attr.batch.elem_flags  = OPTS_GET(opts, elem_flags, 0);
 	attr.batch.flags = OPTS_GET(opts, flags, 0);
+	attr.batch.cpu = OPTS_GET(opts, cpu, 0);
 
 	ret = sys_bpf(cmd, &attr, attr_sz);
 	*count = attr.batch.count;
diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
index 7252150e7ad3..d0ab18b50294 100644
--- a/tools/lib/bpf/bpf.h
+++ b/tools/lib/bpf/bpf.h
@@ -163,12 +163,42 @@ LIBBPF_API int bpf_map_delete_elem_flags(int fd, const void *key, __u64 flags);
 LIBBPF_API int bpf_map_get_next_key(int fd, const void *key, void *next_key);
 LIBBPF_API int bpf_map_freeze(int fd);
 
+/**
+ * @brief **bpf_map_update_elem_opts** allows for updating map with options.
+ *
+ * @param fd BPF map file descriptor
+ * @param key pointer to key
+ * @param value pointer to value
+ * @param opts options for configuring the way to update map
+ * @return 0, on success; negative error code, otherwise (errno is also set to
+ * the error code)
+ */
+LIBBPF_API int bpf_map_update_elem_opts(int fd, const void *key, const void *value,
+					const struct bpf_map_update_elem_opts *opts);
+
+/**
+ * @brief **bpf_map_lookup_elem_opts** allows for looking up the value with
+ * options.
+ *
+ * @param fd BPF map file descriptor
+ * @param key pointer to key
+ * @param value pointer to value
+ * @param opts options for configuring the way to lookup map
+ * @return 0, on success; negative error code, otherwise (errno is also set to
+ * the error code)
+ */
+LIBBPF_API int bpf_map_lookup_elem_opts(int fd, const void *key, void *value,
+					const struct bpf_map_lookup_elem_opts *opts);
+
+
 struct bpf_map_batch_opts {
 	size_t sz; /* size of this struct for forward/backward compatibility */
 	__u64 elem_flags;
 	__u64 flags;
+	__u32 cpu;
+	size_t:0;
 };
-#define bpf_map_batch_opts__last_field flags
+#define bpf_map_batch_opts__last_field cpu
 
 
 /**
@@ -286,6 +316,10 @@ 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, update value across all CPUs if **opts->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 aee36402f0a3..35faedef6ab4 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -10582,7 +10582,8 @@ 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;
@@ -10601,6 +10602,19 @@ 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;
+		if (cpu != BPF_ALL_CPUS && cpu >= libbpf_num_possible_cpus())
+			return -E2BIG;
+		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:
@@ -10633,32 +10647,62 @@ 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, 0, 0);
 	if (err)
 		return libbpf_err(err);
 
 	return bpf_map_lookup_elem_flags(map->fd, key, value, flags);
 }
 
+int bpf_map__lookup_elem_opts(const struct bpf_map *map, const void *key,
+			      size_t key_sz, void *value, size_t value_sz,
+			      const struct bpf_map_lookup_elem_opts *opts)
+{
+	__u64 flags = OPTS_GET(opts, flags, 0);
+	__u32 cpu = OPTS_GET(opts, cpu, 0);
+	int err;
+
+	err = validate_map_op(map, key_sz, value_sz, true, flags, cpu);
+	if (err)
+		return libbpf_err(err);
+
+	return bpf_map_lookup_elem_opts(map->fd, key, value, opts);
+}
+
 int bpf_map__update_elem(const struct bpf_map *map,
 			 const void *key, size_t key_sz,
 			 const void *value, size_t value_sz, __u64 flags)
 {
 	int err;
 
-	err = validate_map_op(map, key_sz, value_sz, true);
+	err = validate_map_op(map, key_sz, value_sz, true, 0, 0);
 	if (err)
 		return libbpf_err(err);
 
 	return bpf_map_update_elem(map->fd, key, value, flags);
 }
 
+int bpf_map__update_elem_opts(const struct bpf_map *map, const void *key,
+			      size_t key_sz, const void *value, size_t value_sz,
+			      const struct bpf_map_update_elem_opts *opts)
+{
+	__u64 flags = OPTS_GET(opts, flags, 0);
+	__u32 cpu = OPTS_GET(opts, cpu, 0);
+	int err;
+
+	err = validate_map_op(map, key_sz, value_sz, true, flags, cpu);
+	if (err)
+		return libbpf_err(err);
+
+	return bpf_map_update_elem_opts(map->fd, key, value, opts);
+}
+
 int bpf_map__delete_elem(const struct bpf_map *map,
 			 const void *key, size_t key_sz, __u64 flags)
 {
 	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, 0);
 	if (err)
 		return libbpf_err(err);
 
@@ -10671,7 +10715,7 @@ 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, 0);
 	if (err)
 		return libbpf_err(err);
 
@@ -10683,7 +10727,7 @@ 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, 0);
 	if (err)
 		return libbpf_err(err);
 
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index d1cf813a057b..fd4940759bc9 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -1168,13 +1168,7 @@ LIBBPF_API struct bpf_map *bpf_map__inner_map(struct bpf_map *map);
  * @param key pointer to memory containing bytes of the key used for lookup
  * @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
- * alignment reasons, so expected size is: `round_up(value_size, 8)
- * * libbpf_num_possible_cpus()`.
+ * @param value_sz refer to **bpf_map__lookup_elem_opts()**'s description.
  * @flags extra flags passed to kernel for this operation
  * @return 0, on success; negative error, otherwise
  *
@@ -1185,6 +1179,32 @@ LIBBPF_API int bpf_map__lookup_elem(const struct bpf_map *map,
 				    const void *key, size_t key_sz,
 				    void *value, size_t value_sz, __u64 flags);
 
+/**
+ * @brief **bpf_map__lookup_elem_opts()** allows to lookup BPF map value
+ * corresponding to provided key with options.
+ * @param map BPF map to lookup element in
+ * @param key pointer to memory containing bytes of the key used for lookup
+ * @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 can be
+ * definition's **value_size** if **BPF_F_CPU** is specified in **opts->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()`.
+ * @opts extra options passed to kernel for this operation
+ * @return 0, on success; negative error, otherwise
+ *
+ * **bpf_map__lookup_elem_opts()** is high-level equivalent of
+ * **bpf_map_lookup_elem_opts()** API with added check for key and value size.
+ */
+LIBBPF_API int bpf_map__lookup_elem_opts(const struct bpf_map *map,
+					 const void *key, size_t key_sz,
+					 void *value, size_t value_sz,
+					 const struct bpf_map_lookup_elem_opts *opts);
+
 /**
  * @brief **bpf_map__update_elem()** allows to insert or update value in BPF
  * map that corresponds to provided key.
@@ -1209,6 +1229,25 @@ LIBBPF_API int bpf_map__update_elem(const struct bpf_map *map,
 				    const void *key, size_t key_sz,
 				    const void *value, size_t value_sz, __u64 flags);
 
+/**
+ * @brief **bpf_map__update_elem_opts()** allows to insert or update value in BPF
+ * map that corresponds to provided key with options.
+ * @param map BPF map to insert to or update element in
+ * @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 refer to **bpf_map__lookup_elem_opts()**'s description.
+ * @opts extra options passed to kernel for this operation
+ * @return 0, on success; negative error, otherwise
+ *
+ * **bpf_map__update_elem_opts()** is high-level equivalent of
+ * **bpf_map_update_elem_opts()** API with added check for key and value size.
+ */
+LIBBPF_API int bpf_map__update_elem_opts(const struct bpf_map *map,
+					 const void *key, size_t key_sz,
+					 const void *value, size_t value_sz,
+					 const struct bpf_map_update_elem_opts *opts);
+
 /**
  * @brief **bpf_map__delete_elem()** allows to delete element in BPF map that
  * corresponds to provided key.
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index d7bd463e7017..fa415d9f26ce 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -448,4 +448,9 @@ LIBBPF_1.6.0 {
 } LIBBPF_1.5.0;
 
 LIBBPF_1.7.0 {
+	global:
+		bpf_map__lookup_elem_opts;
+		bpf_map__update_elem_opts;
+		bpf_map_lookup_elem_opts;
+		bpf_map_update_elem_opts;
 } LIBBPF_1.6.0;
diff --git a/tools/lib/bpf/libbpf_common.h b/tools/lib/bpf/libbpf_common.h
index 8fe248e14eb6..84ca89ace1be 100644
--- a/tools/lib/bpf/libbpf_common.h
+++ b/tools/lib/bpf/libbpf_common.h
@@ -89,4 +89,18 @@
 		memcpy(&NAME, &___##NAME, sizeof(NAME));		    \
 	} while (0)
 
+struct bpf_map_update_elem_opts {
+	size_t sz; /* size of this struct for forward/backward compatibility */
+	__u64 flags;
+	__u32 cpu;
+	size_t:0;
+};
+
+struct bpf_map_lookup_elem_opts {
+	size_t sz; /* size of this struct for forward/backward compatibility */
+	__u64 flags;
+	__u32 cpu;
+	size_t:0;
+};
+
 #endif /* __LIBBPF_LIBBPF_COMMON_H */
-- 
2.50.1

[PATCH bpf-next 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_opts()
* bpf_map__update_elem_opts()
* bpf_map_lookup_elem_opts()
* bpf_map__lookup_elem_opts()

cd tools/testing/selftests/bpf/
./test_progs -t percpu_alloc/cpu_flag_tests
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   | 172 ++++++++++++++++++
 .../selftests/bpf/progs/percpu_array_flag.c   |  24 +++
 2 files changed, 196 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 343da65864d6..2bf4e6f1d357 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 +116,175 @@ 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);
+	struct percpu_array_flag *skel;
+	u64 batch = 0, *values = NULL;
+	const u64 value = 0xDEADC0DE;
+	u32 count, max_entries;
+	struct bpf_map *map;
+	LIBBPF_OPTS(bpf_map_lookup_elem_opts, lookup_opts,
+		    .flags = BPF_F_CPU,
+		    .cpu = 0,
+	);
+	LIBBPF_OPTS(bpf_map_update_elem_opts, update_opts,
+		    .flags = BPF_F_CPU,
+		    .cpu = 0,
+	);
+	LIBBPF_OPTS(bpf_map_batch_opts, batch_opts,
+		    .elem_flags = BPF_F_CPU,
+		    .flags = 0,
+	);
+
+	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.cpu = nr_cpus;
+	err = bpf_map_update_batch(map_fd, keys, values, &max_entries, &batch_opts);
+	if (!ASSERT_EQ(err, -E2BIG, "bpf_map_update_batch -E2BIG"))
+		goto out;
+
+	for (cpu = 0; cpu < nr_cpus; cpu++) {
+		memset(values, 0, max_entries * value_size);
+
+		/* clear values on all CPUs */
+		batch_opts.cpu = BPF_ALL_CPUS;
+		batch_opts.elem_flags = 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 current CPU */
+		for (i = 0; i < max_entries; i++)
+			values[i] = value;
+
+		batch_opts.cpu = cpu;
+		err = bpf_map_update_batch(map_fd, keys, values, &max_entries, &batch_opts);
+		if (!ASSERT_OK(err, "bpf_map_update_batch current cpu"))
+			goto out;
+
+		/* lookup values on current CPU */
+		batch_opts.cpu = cpu;
+		batch_opts.elem_flags = BPF_F_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 current cpu"))
+			goto out;
+
+		for (i = 0; i < max_entries; i++)
+			if (!ASSERT_EQ(values[i], value, "value on current cpu"))
+				goto out;
+
+		/* lookup values on all CPUs */
+		batch_opts.cpu = 0;
+		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 cpu"))
+					goto out;
+			}
+		}
+	}
+
+	update_opts.cpu = nr_cpus;
+	err = bpf_map_update_elem_opts(map_fd, keys, values, &update_opts);
+	if (!ASSERT_EQ(err, -E2BIG, "bpf_map_update_elem_opts -E2BIG"))
+		goto out;
+
+	err = bpf_map__update_elem_opts(map, keys, key_sz, values, value_sz,
+					&update_opts);
+	if (!ASSERT_EQ(err, -E2BIG, "bpf_map__update_elem_opts -E2BIG"))
+		goto out;
+
+	lookup_opts.cpu = nr_cpus;
+	err = bpf_map_lookup_elem_opts(map_fd, keys, values, &lookup_opts);
+	if (!ASSERT_EQ(err, -E2BIG, "bpf_map_lookup_elem_opts -E2BIG"))
+		goto out;
+
+	err = bpf_map__lookup_elem_opts(map, keys, key_sz, values, value_sz,
+					&lookup_opts);
+	if (!ASSERT_EQ(err, -E2BIG, "bpf_map__lookup_elem_opts -E2BIG"))
+		goto out;
+
+	/* clear value on all cpus */
+	batch_opts.cpu = BPF_ALL_CPUS;
+	batch_opts.elem_flags = 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 current cpu */
+		values[0] = value;
+		update_opts.cpu = cpu;
+		for (i = 0; i < max_entries; i++) {
+			err = bpf_map__update_elem_opts(map, keys + i,
+							key_sz, values,
+							value_sz, &update_opts);
+			if (!ASSERT_OK(err, "bpf_map__update_elem_opts current cpu"))
+				goto out;
+
+			for (j = 0; j < nr_cpus; j++) {
+				/* lookup then check value on CPUs */
+				lookup_opts.cpu = j;
+				err = bpf_map__lookup_elem_opts(map, keys + i,
+								key_sz, values,
+								value_sz,
+								&lookup_opts);
+				if (!ASSERT_OK(err, "bpf_map__lookup_elem_opts current cpu"))
+					goto out;
+				if (!ASSERT_EQ(values[0], j != cpu ? 0 : value,
+					       "bpf_map__lookup_elem_opts value on current cpu"))
+					goto out;
+			}
+		}
+
+		/* clear value on current cpu */
+		values[0] = 0;
+		err = bpf_map__update_elem_opts(map, keys, key_sz, values,
+						value_sz, &update_opts);
+		if (!ASSERT_OK(err, "bpf_map__update_elem_opts current 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 +295,6 @@ 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 000000000000..4d92e121958e
--- /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 1/3] bpf: Introduce BPF_F_CPU flag for percpu_array map

[Andrii Nakryiko]

On Thu, Jul 17, 2025 at 12:38 PM Leon Hwang <leon.hwang@linux.dev> wrote:
>
> This patch introduces support for the BPF_F_CPU flag in percpu_array maps
> to allow updating or looking up values for specified CPUs 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 separated cpu field.
>
> Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
> ---
>  include/linux/bpf.h            |  3 +-
>  include/uapi/linux/bpf.h       |  7 +++++
>  kernel/bpf/arraymap.c          | 54 ++++++++++++++++++++++++++--------
>  kernel/bpf/syscall.c           | 52 ++++++++++++++++++++------------
>  tools/include/uapi/linux/bpf.h |  7 +++++
>  5 files changed, 90 insertions(+), 33 deletions(-)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index f9cd2164ed23..faee5710e913 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -2671,7 +2671,8 @@ 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 233de8677382..4cad3de6899d 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 */
> @@ -1549,6 +1555,7 @@ union bpf_attr {
>                 __u32           map_fd;
>                 __u64           elem_flags;
>                 __u64           flags;
> +               __u32           cpu;
>         } batch;

So you use flags to pass cpu for singular lookup/delete operations,
but separate cpu field for batch. We need to be consistent here. I
think I initially suggested a separate cpu field, but given how much
churn it's causing in API and usage, I guess I'm leaning towards just
passing it through flags.

But if someone else has strong preferences, I can be convinced otherwise.

Either way, it has to be consistent between batched and non-batched API.

Other than that and minor formatting needs below, LGTM.

pw-bot: cr

>
>         struct { /* anonymous struct used by BPF_PROG_LOAD command */
> diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
> index 3d080916faf9..d333663cbe71 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 = (u32)(flags >> 32);
> +       flags &= (u32)~0;
> +       if (unlikely(flags > BPF_F_CPU))
> +               return -EINVAL;
> +       if (unlikely((flags & BPF_F_CPU) && cpu >= num_possible_cpus()))
> +               return -E2BIG;

nit: I'd probably do -ERANGE for this one

> +
>         /* 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

[...]

> @@ -1941,19 +1945,25 @@ int generic_map_update_batch(struct bpf_map *map, struct file *map_file,
>  {
>         void __user *values = u64_to_user_ptr(attr->batch.values);
>         void __user *keys = u64_to_user_ptr(attr->batch.keys);
> -       u32 value_size, cp, max_count;
> +       u32 value_size, cp, max_count, cpu = attr->batch.cpu;
> +       u64 elem_flags = attr->batch.elem_flags;
>         void *key, *value;
>         int err = 0;
>
> -       if (attr->batch.elem_flags & ~BPF_F_LOCK)
> +       if (elem_flags & ~(BPF_F_LOCK | BPF_F_CPU))
>                 return -EINVAL;
>
> -       if ((attr->batch.elem_flags & BPF_F_LOCK) &&
> +       if ((elem_flags & BPF_F_LOCK) &&
>             !btf_record_has_field(map->record, BPF_SPIN_LOCK)) {
>                 return -EINVAL;
>         }
>
> -       value_size = bpf_map_value_size(map);
> +       if ((elem_flags & BPF_F_CPU) &&
> +               map->map_type != BPF_MAP_TYPE_PERCPU_ARRAY)

nit: keep on the single line

> +               return -EINVAL;
> +
> +       value_size = bpf_map_value_size(map, elem_flags);
> +       elem_flags |= ((u64)cpu) << 32;
>
>         max_count = attr->batch.count;
>         if (!max_count)

[...]

> -       if ((attr->batch.elem_flags & BPF_F_LOCK) &&
> +       if ((elem_flags & BPF_F_LOCK) &&
>             !btf_record_has_field(map->record, BPF_SPIN_LOCK))
>                 return -EINVAL;
>
> -       value_size = bpf_map_value_size(map);
> +       if ((elem_flags & BPF_F_CPU) &&
> +               map->map_type != BPF_MAP_TYPE_PERCPU_ARRAY)
> +               return -EINVAL;

same, formatting is off, but best to keep it single line

> +
> +       value_size = bpf_map_value_size(map, elem_flags);
> +       elem_flags |= ((u64)cpu) << 32;
>
>         max_count = attr->batch.count;
>         if (!max_count)

[...]

Re: [PATCH bpf-next 2/3] bpf, libbpf: Support BPF_F_CPU for percpu_array map

[Andrii Nakryiko]

On Thu, Jul 17, 2025 at 12:38 PM Leon Hwang <leon.hwang@linux.dev> wrote:
>
> This patch adds libbpf support for the BPF_F_CPU flag in percpu_array maps,
> introducing the following APIs:
>
> 1. bpf_map_update_elem_opts(): update with struct bpf_map_update_elem_opts
> 2. bpf_map_lookup_elem_opts(): lookup with struct bpf_map_lookup_elem_opts
> 3. bpf_map__update_elem_opts(): high-level wrapper with input validation
> 4. bpf_map__lookup_elem_opts(): high-level wrapper with input validation
>
> Behavior:
>
> * If opts->cpu == (u32)~0, the update is applied to all CPUs.
> * Otherwise, it applies only to the specified CPU.
> * Lookup APIs retrieve values from the target CPU when BPF_F_CPU is used.
>
> Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
> ---

please use "libbpf: " prefix, not "bpf,libbpf:"


Then see my comment on flags vs separate field for cpu passing. If we
go with just using flags, then I'd probably drop all the new libbpf
APIs, because we already have bpf_map_lookup_elem_flags() and
bpf_map_update_elem() (the latter accepts flags), so as far as
low-level API we are good.

The comment describing the new BPF_F_CPU flag is good, so let's add
it, but place it into bpf_map__lookup_elem() description (which, btw,
also accepts flags, so no changes to API itself is necessary). Same
for bpf_map__update_elem().

validate_map_op() logic will stay, but just will extract cpu from flags, right?

So overall less API churn, but same possibilities for users (plus we
get better documentation, which is always nice).

>  tools/lib/bpf/bpf.c           | 23 ++++++++++++++
>  tools/lib/bpf/bpf.h           | 36 +++++++++++++++++++++-
>  tools/lib/bpf/libbpf.c        | 56 +++++++++++++++++++++++++++++++----
>  tools/lib/bpf/libbpf.h        | 53 ++++++++++++++++++++++++++++-----
>  tools/lib/bpf/libbpf.map      |  5 ++++
>  tools/lib/bpf/libbpf_common.h | 14 +++++++++
>  6 files changed, 173 insertions(+), 14 deletions(-)
>

[...]

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

[Leon Hwang]

On 2025/7/18 23:52, Andrii Nakryiko wrote:
> On Thu, Jul 17, 2025 at 12:38 PM Leon Hwang <leon.hwang@linux.dev> wrote:
>>
>> This patch introduces support for the BPF_F_CPU flag in percpu_array maps
>> to allow updating or looking up values for specified CPUs 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 separated cpu field.
>>
>> Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
>> ---
>>  include/linux/bpf.h            |  3 +-
>>  include/uapi/linux/bpf.h       |  7 +++++
>>  kernel/bpf/arraymap.c          | 54 ++++++++++++++++++++++++++--------
>>  kernel/bpf/syscall.c           | 52 ++++++++++++++++++++------------
>>  tools/include/uapi/linux/bpf.h |  7 +++++
>>  5 files changed, 90 insertions(+), 33 deletions(-)
>>
>> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
>> index f9cd2164ed23..faee5710e913 100644
>> --- a/include/linux/bpf.h
>> +++ b/include/linux/bpf.h
>> @@ -2671,7 +2671,8 @@ 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 233de8677382..4cad3de6899d 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 */
>> @@ -1549,6 +1555,7 @@ union bpf_attr {
>>                 __u32           map_fd;
>>                 __u64           elem_flags;
>>                 __u64           flags;
>> +               __u32           cpu;
>>         } batch;
> 
> So you use flags to pass cpu for singular lookup/delete operations,
> but separate cpu field for batch. We need to be consistent here. I
> think I initially suggested a separate cpu field, but given how much
> churn it's causing in API and usage, I guess I'm leaning towards just
> passing it through flags.
> 
> But if someone else has strong preferences, I can be convinced otherwise.
> 

Sure, they should be consistent.

Passing the CPU info through flags was actually my original idea, but I
wasn’t sure how to convince you initially.

Let’s go ahead and pass the CPU through flags to minimize churn.

> Either way, it has to be consistent between batched and non-batched API.
> 
> Other than that and minor formatting needs below, LGTM.
> 
> pw-bot: cr
> 
>>
>>         struct { /* anonymous struct used by BPF_PROG_LOAD command */
>> diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
>> index 3d080916faf9..d333663cbe71 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 = (u32)(flags >> 32);
>> +       flags &= (u32)~0;
>> +       if (unlikely(flags > BPF_F_CPU))
>> +               return -EINVAL;
>> +       if (unlikely((flags & BPF_F_CPU) && cpu >= num_possible_cpus()))
>> +               return -E2BIG;
> 
> nit: I'd probably do -ERANGE for this one
> 

Ack.

>> +
>>         /* 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
> 
> [...]
> 
>> @@ -1941,19 +1945,25 @@ int generic_map_update_batch(struct bpf_map *map, struct file *map_file,
>>  {
>>         void __user *values = u64_to_user_ptr(attr->batch.values);
>>         void __user *keys = u64_to_user_ptr(attr->batch.keys);
>> -       u32 value_size, cp, max_count;
>> +       u32 value_size, cp, max_count, cpu = attr->batch.cpu;
>> +       u64 elem_flags = attr->batch.elem_flags;
>>         void *key, *value;
>>         int err = 0;
>>
>> -       if (attr->batch.elem_flags & ~BPF_F_LOCK)
>> +       if (elem_flags & ~(BPF_F_LOCK | BPF_F_CPU))
>>                 return -EINVAL;
>>
>> -       if ((attr->batch.elem_flags & BPF_F_LOCK) &&
>> +       if ((elem_flags & BPF_F_LOCK) &&
>>             !btf_record_has_field(map->record, BPF_SPIN_LOCK)) {
>>                 return -EINVAL;
>>         }
>>
>> -       value_size = bpf_map_value_size(map);
>> +       if ((elem_flags & BPF_F_CPU) &&
>> +               map->map_type != BPF_MAP_TYPE_PERCPU_ARRAY)
> 
> nit: keep on the single line
> 

Ack.

Btw, how many chars of one line do we allow? 100 chars?

>> +               return -EINVAL;
>> +
>> +       value_size = bpf_map_value_size(map, elem_flags);
>> +       elem_flags |= ((u64)cpu) << 32;
>>
>>         max_count = attr->batch.count;
>>         if (!max_count)
> 
> [...]
> 
>> -       if ((attr->batch.elem_flags & BPF_F_LOCK) &&
>> +       if ((elem_flags & BPF_F_LOCK) &&
>>             !btf_record_has_field(map->record, BPF_SPIN_LOCK))
>>                 return -EINVAL;
>>
>> -       value_size = bpf_map_value_size(map);
>> +       if ((elem_flags & BPF_F_CPU) &&
>> +               map->map_type != BPF_MAP_TYPE_PERCPU_ARRAY)
>> +               return -EINVAL;
> 
> same, formatting is off, but best to keep it single line
> 

Ack.

[...]

Thanks,
Leon

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

[Eduard Zingerman]

On Tue, 2025-07-22 at 01:08 +0800, Leon Hwang wrote:

[...]

> > > @@ -1941,19 +1945,25 @@ int generic_map_update_batch(struct bpf_map *map, struct file *map_file,
> > >  {
> > >         void __user *values = u64_to_user_ptr(attr->batch.values);
> > >         void __user *keys = u64_to_user_ptr(attr->batch.keys);
> > > -       u32 value_size, cp, max_count;
> > > +       u32 value_size, cp, max_count, cpu = attr->batch.cpu;
> > > +       u64 elem_flags = attr->batch.elem_flags;
> > >         void *key, *value;
> > >         int err = 0;
> > > 
> > > -       if (attr->batch.elem_flags & ~BPF_F_LOCK)
> > > +       if (elem_flags & ~(BPF_F_LOCK | BPF_F_CPU))
> > >                 return -EINVAL;
> > > 
> > > -       if ((attr->batch.elem_flags & BPF_F_LOCK) &&
> > > +       if ((elem_flags & BPF_F_LOCK) &&
> > >             !btf_record_has_field(map->record, BPF_SPIN_LOCK)) {
> > >                 return -EINVAL;
> > >         }
> > > 
> > > -       value_size = bpf_map_value_size(map);
> > > +       if ((elem_flags & BPF_F_CPU) &&
> > > +               map->map_type != BPF_MAP_TYPE_PERCPU_ARRAY)
> > 
> > nit: keep on the single line
> > 
> 
> Ack.
> 
> Btw, how many chars of one line do we allow? 100 chars?

Yes, 100 chars per line (Andrii is on PTO).

Re: [PATCH bpf-next 2/3] bpf, libbpf: Support BPF_F_CPU for percpu_array map

[Leon Hwang]

On 2025/7/18 23:57, Andrii Nakryiko wrote:
> On Thu, Jul 17, 2025 at 12:38 PM Leon Hwang <leon.hwang@linux.dev> wrote:
>>
>> This patch adds libbpf support for the BPF_F_CPU flag in percpu_array maps,
>> introducing the following APIs:
>>
>> 1. bpf_map_update_elem_opts(): update with struct bpf_map_update_elem_opts
>> 2. bpf_map_lookup_elem_opts(): lookup with struct bpf_map_lookup_elem_opts
>> 3. bpf_map__update_elem_opts(): high-level wrapper with input validation
>> 4. bpf_map__lookup_elem_opts(): high-level wrapper with input validation
>>
>> Behavior:
>>
>> * If opts->cpu == (u32)~0, the update is applied to all CPUs.
>> * Otherwise, it applies only to the specified CPU.
>> * Lookup APIs retrieve values from the target CPU when BPF_F_CPU is used.
>>
>> Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
>> ---
> 
> please use "libbpf: " prefix, not "bpf,libbpf:"
> 

Ack.

> 
> Then see my comment on flags vs separate field for cpu passing. If we
> go with just using flags, then I'd probably drop all the new libbpf
> APIs, because we already have bpf_map_lookup_elem_flags() and
> bpf_map_update_elem() (the latter accepts flags), so as far as
> low-level API we are good.
> 

All the new libbpf APIs are unnecessary when pass the cpu through flags.

> The comment describing the new BPF_F_CPU flag is good, so let's add
> it, but place it into bpf_map__lookup_elem() description (which, btw,
> also accepts flags, so no changes to API itself is necessary). Same
> for bpf_map__update_elem().
> 

No problem.

> validate_map_op() logic will stay, but just will extract cpu from flags, right?
> 

Yes, it is.

> So overall less API churn, but same possibilities for users (plus we
> get better documentation, which is always nice).
> 

When users want to use this feature, they should follow the libbpf API's
documentation, no matter whether the cpu is separated or flags-embedded.

Thanks,
Leon

>>  tools/lib/bpf/bpf.c           | 23 ++++++++++++++
>>  tools/lib/bpf/bpf.h           | 36 +++++++++++++++++++++-
>>  tools/lib/bpf/libbpf.c        | 56 +++++++++++++++++++++++++++++++----
>>  tools/lib/bpf/libbpf.h        | 53 ++++++++++++++++++++++++++++-----
>>  tools/lib/bpf/libbpf.map      |  5 ++++
>>  tools/lib/bpf/libbpf_common.h | 14 +++++++++
>>  6 files changed, 173 insertions(+), 14 deletions(-)
>>
> 
> [...]

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

[Leon Hwang]

On 2025/7/22 01:11, Eduard Zingerman wrote:
> On Tue, 2025-07-22 at 01:08 +0800, Leon Hwang wrote:
> 
> [...]
> 
>>>> @@ -1941,19 +1945,25 @@ int generic_map_update_batch(struct bpf_map *map, struct file *map_file,
>>>>  {
>>>>         void __user *values = u64_to_user_ptr(attr->batch.values);
>>>>         void __user *keys = u64_to_user_ptr(attr->batch.keys);
>>>> -       u32 value_size, cp, max_count;
>>>> +       u32 value_size, cp, max_count, cpu = attr->batch.cpu;
>>>> +       u64 elem_flags = attr->batch.elem_flags;
>>>>         void *key, *value;
>>>>         int err = 0;
>>>>
>>>> -       if (attr->batch.elem_flags & ~BPF_F_LOCK)
>>>> +       if (elem_flags & ~(BPF_F_LOCK | BPF_F_CPU))
>>>>                 return -EINVAL;
>>>>
>>>> -       if ((attr->batch.elem_flags & BPF_F_LOCK) &&
>>>> +       if ((elem_flags & BPF_F_LOCK) &&
>>>>             !btf_record_has_field(map->record, BPF_SPIN_LOCK)) {
>>>>                 return -EINVAL;
>>>>         }
>>>>
>>>> -       value_size = bpf_map_value_size(map);
>>>> +       if ((elem_flags & BPF_F_CPU) &&
>>>> +               map->map_type != BPF_MAP_TYPE_PERCPU_ARRAY)
>>>
>>> nit: keep on the single line
>>>
>>
>> Ack.
>>
>> Btw, how many chars of one line do we allow? 100 chars?
> 
> Yes, 100 chars per line (Andrii is on PTO).

Hi Eduard,

Thank you for your reply.

I’ll keep that in mind for the future.

Thanks,
Leon