On Thu, Aug 21, 2025 at 9:08 AM Leon Hwang <leon.hwang@xxxxxxxxx> wrote:
>
> Introduce support for the BPF_F_ALL_CPUS flag in percpu_array maps to
> allow updating values for all CPUs with a single value.
>
> Introduce support for the BPF_F_CPU flag in percpu_array maps to allow
> updating value for specified CPU.
>
> This enhancement enables:
>
> * Efficient update values across all CPUs with a single value when
> BPF_F_ALL_CPUS is set for update_elem and update_batch APIs.
> * Targeted update or lookup for a specified CPU when BPF_F_CPU is set.
>
> The BPF_F_CPU flag is passed via:
>
> * map_flags of lookup_elem and update_elem APIs along with embedded cpu
> field.
> * elem_flags of lookup_batch and update_batch APIs along with embedded
> cpu field.
>
> Signed-off-by: Leon Hwang <leon.hwang@xxxxxxxxx>
> ---
> include/linux/bpf.h | 3 +-
> include/uapi/linux/bpf.h | 2 ++
> kernel/bpf/arraymap.c | 56 ++++++++++++++++++++++++++--------
> kernel/bpf/syscall.c | 27 ++++++++++------
> tools/include/uapi/linux/bpf.h | 2 ++
> 5 files changed, 67 insertions(+), 23 deletions(-)
>
[...]
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 19f7f5de5e7dc..6251ac9bc7e42 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -131,9 +131,11 @@ bool bpf_map_write_active(const struct bpf_map *map)
> return atomic64_read(&map->writecnt) != 0;
> }
>
> -static u32 bpf_map_value_size(const struct bpf_map *map)
> +static u32 bpf_map_value_size(const struct bpf_map *map, u64 flags)
> {
> - if (map->map_type == BPF_MAP_TYPE_PERCPU_HASH ||
> + if (map->map_type == BPF_MAP_TYPE_PERCPU_ARRAY && (flags & (BPF_F_CPU | BPF_F_ALL_CPUS)))
> + return round_up(map->value_size, 8);
this doesn't depend on the PERCPU_ARRAY map type, right? Any map for
which we allowed BPF_F_CPU or BPF_F_ALL_CPUS would use this formula?
(and if map doesn't support those flags, you should have filtered that
out earlier, no?) So maybe add this is first separate condition before
all this map type specific logic?
> + else if (map->map_type == BPF_MAP_TYPE_PERCPU_HASH ||
> map->map_type == BPF_MAP_TYPE_LRU_PERCPU_HASH ||
> map->map_type == BPF_MAP_TYPE_PERCPU_ARRAY ||
> map->map_type == BPF_MAP_TYPE_PERCPU_CGROUP_STORAGE)
> @@ -314,7 +316,7 @@ static int bpf_map_copy_value(struct bpf_map *map, void *key, void *value,
> map->map_type == BPF_MAP_TYPE_LRU_PERCPU_HASH) {
> err = bpf_percpu_hash_copy(map, key, value);
> } else if (map->map_type == BPF_MAP_TYPE_PERCPU_ARRAY) {
> - err = bpf_percpu_array_copy(map, key, value);
> + err = bpf_percpu_array_copy(map, key, value, flags);
> } else if (map->map_type == BPF_MAP_TYPE_PERCPU_CGROUP_STORAGE) {
> err = bpf_percpu_cgroup_storage_copy(map, key, value);
> } else if (map->map_type == BPF_MAP_TYPE_STACK_TRACE) {
> @@ -1656,12 +1658,19 @@ static void *___bpf_copy_key(bpfptr_t ukey, u64 key_size)
>
> static int check_map_flags(struct bpf_map *map, u64 flags, bool check_flag)
you are later moving this into bpf.h header, so do it in previous
patch early on, less unnecessary code churn and easier to review
actual changes to that function in subsequent patches
> {
> - if (check_flag && (flags & ~BPF_F_LOCK))
> + if (check_flag && ((u32)flags & ~(BPF_F_LOCK | BPF_F_CPU | BPF_F_ALL_CPUS)))
> return -EINVAL;
>
> if ((flags & BPF_F_LOCK) && !btf_record_has_field(map->record, BPF_SPIN_LOCK))
> return -EINVAL;
>
> + if (!(flags & BPF_F_CPU) && flags >> 32)
> + return -EINVAL;
> +
> + if ((flags & (BPF_F_CPU | BPF_F_ALL_CPUS)) &&
> + map->map_type != BPF_MAP_TYPE_PERCPU_ARRAY)
> + return -EINVAL;
> +
> return 0;
> }
>
[...]
