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@xxxxxxxxx>
> ---
> 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
>
>
