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Message-ID: <20251117162033.6296-8-leon.hwang@linux.dev>
Date: Tue, 18 Nov 2025 00:20:32 +0800
From: Leon Hwang <leon.hwang@...ux.dev>
To: bpf@...r.kernel.org
Cc: ast@...nel.org,
andrii@...nel.org,
daniel@...earbox.net,
jolsa@...nel.org,
yonghong.song@...ux.dev,
song@...nel.org,
eddyz87@...il.com,
dxu@...uu.xyz,
deso@...teo.net,
martin.lau@...ux.dev,
john.fastabend@...il.com,
kpsingh@...nel.org,
sdf@...ichev.me,
haoluo@...gle.com,
shuah@...nel.org,
kerneljasonxing@...il.com,
chen.dylane@...ux.dev,
willemb@...gle.com,
paul.chaignon@...il.com,
a.s.protopopov@...il.com,
memxor@...il.com,
yatsenko@...a.com,
tklauser@...tanz.ch,
leon.hwang@...ux.dev,
kernel-patches-bot@...com,
linux-kernel@...r.kernel.org,
linux-kselftest@...r.kernel.org
Subject: [PATCH bpf-next v10 7/8] libbpf: Add BPF_F_CPU and BPF_F_ALL_CPUS flags support for percpu maps
Add libbpf support for the BPF_F_CPU flag for percpu 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()
And the flag can be BPF_F_ALL_CPUS, but cannot be
'BPF_F_CPU | BPF_F_ALL_CPUS'.
Behavior:
* If the flag is BPF_F_ALL_CPUS, the update is applied across all CPUs.
* If the flag is BPF_F_CPU, it updates value only to the specified CPU.
* If the flag is BPF_F_CPU, lookup value only from the specified CPU.
* lookup does not support BPF_F_ALL_CPUS.
Acked-by: Andrii Nakryiko <andrii@...nel.org>
Signed-off-by: Leon Hwang <leon.hwang@...ux.dev>
---
tools/lib/bpf/bpf.h | 8 ++++++++
tools/lib/bpf/libbpf.c | 26 ++++++++++++++++++++------
tools/lib/bpf/libbpf.h | 21 ++++++++-------------
3 files changed, 36 insertions(+), 19 deletions(-)
diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
index e983a3e40d612..ffd93feffd71d 100644
--- a/tools/lib/bpf/bpf.h
+++ b/tools/lib/bpf/bpf.h
@@ -289,6 +289,14 @@ 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 maps, update value on the specified CPU. And the cpu
+ * info is embedded into the high 32 bits of **opts->elem_flags**.
+ *
+ * **BPF_F_ALL_CPUS**
+ * As for percpu maps, update value across all CPUs. This flag cannot
+ * be used with BPF_F_CPU at the same time.
+ *
* @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 706e7481bdf6b..65b9b5e955449 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -10913,7 +10913,7 @@ 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)
{
if (!map_is_created(map)) /* map is not yet created */
return -ENOENT;
@@ -10940,6 +10940,20 @@ static int validate_map_op(const struct bpf_map *map, size_t key_sz,
int num_cpu = libbpf_num_possible_cpus();
size_t elem_sz = roundup(map->def.value_size, 8);
+ if (flags & (BPF_F_CPU | BPF_F_ALL_CPUS)) {
+ if ((flags & BPF_F_CPU) && (flags & BPF_F_ALL_CPUS)) {
+ pr_warn("map '%s': BPF_F_CPU and BPF_F_ALL_CPUS are mutually exclusive\n",
+ map->name);
+ return -EINVAL;
+ }
+ if (map->def.value_size != value_sz) {
+ pr_warn("map '%s': unexpected value size %zu provided for either BPF_F_CPU or BPF_F_ALL_CPUS, expected %u\n",
+ map->name, value_sz, map->def.value_size);
+ return -EINVAL;
+ }
+ break;
+ }
+
if (value_sz != num_cpu * elem_sz) {
pr_warn("map '%s': unexpected value size %zu provided for per-CPU map, expected %d * %zu = %zd\n",
map->name, value_sz, num_cpu, elem_sz, num_cpu * elem_sz);
@@ -10964,7 +10978,7 @@ 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);
@@ -10977,7 +10991,7 @@ 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);
@@ -10989,7 +11003,7 @@ 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 */, flags);
if (err)
return libbpf_err(err);
@@ -11002,7 +11016,7 @@ 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, flags);
if (err)
return libbpf_err(err);
@@ -11014,7 +11028,7 @@ 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 5118d0a90e243..7c38b2e546080 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -1196,12 +1196,13 @@ 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
- * alignment reasons, so expected size is: `round_up(value_size, 8)
- * * libbpf_num_possible_cpus()`.
+ * definition's **value_size**. For per-CPU BPF maps, value size can be
+ * `value_size` if either **BPF_F_CPU** or **BPF_F_ALL_CPUS** 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 also that for per-CPU values value
+ * size has to be aligned up to closest 8 bytes, so expected size is:
+ * `round_up(value_size, 8) * libbpf_num_possible_cpus()`.
* @flags extra flags passed to kernel for this operation
* @return 0, on success; negative error, otherwise
*
@@ -1219,13 +1220,7 @@ 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
*
--
2.51.2
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