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Message-ID: <CAADnVQKuWrS57niXtr-xu4daR=GvnZORa+X2gHkDbsDZ3qyveQ@mail.gmail.com>
Date: Tue, 25 Nov 2025 15:21:04 -0800
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Leon Hwang <leon.hwang@...ux.dev>
Cc: bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
Andrii Nakryiko <andrii@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, Jiri Olsa <jolsa@...nel.org>,
Yonghong Song <yonghong.song@...ux.dev>, Song Liu <song@...nel.org>, Eduard <eddyz87@...il.com>,
Daniel Xu <dxu@...uu.xyz>, Daniel Müller <deso@...teo.net>,
Martin KaFai Lau <martin.lau@...ux.dev>, John Fastabend <john.fastabend@...il.com>,
KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>,
Shuah Khan <shuah@...nel.org>, Jason Xing <kerneljasonxing@...il.com>,
Tao Chen <chen.dylane@...ux.dev>, Willem de Bruijn <willemb@...gle.com>,
Paul Chaignon <paul.chaignon@...il.com>, Anton Protopopov <a.s.protopopov@...il.com>,
Kumar Kartikeya Dwivedi <memxor@...il.com>, Mykyta Yatsenko <yatsenko@...a.com>,
Tobias Klauser <tklauser@...tanz.ch>, kernel-patches-bot@...com,
LKML <linux-kernel@...r.kernel.org>,
"open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH bpf-next v11 2/8] bpf: Introduce BPF_F_CPU and
BPF_F_ALL_CPUS flags
On Tue, Nov 25, 2025 at 6:59 AM Leon Hwang <leon.hwang@...ux.dev> wrote:
>
> Introduce BPF_F_CPU and BPF_F_ALL_CPUS flags and check them for
> following APIs:
>
> * 'map_lookup_elem()'
> * 'map_update_elem()'
> * 'generic_map_lookup_batch()'
> * 'generic_map_update_batch()'
>
> And, get the correct value size for these APIs.
>
> Acked-by: Andrii Nakryiko <andrii@...nel.org>
> Signed-off-by: Leon Hwang <leon.hwang@...ux.dev>
> ---
> v10 -> v11:
> - Use '(BPF_F_ALL_CPUS << 1) - 1' as allowed_flags in map_update_elem().
> - Add BPF_EXIST to allowed_flags in generic_map_update_batch().
It should be mentioned in the commit log.
Lines after --- don't stay in the log.
> ---
> include/linux/bpf.h | 23 +++++++++++++++++++++-
> include/uapi/linux/bpf.h | 2 ++
> kernel/bpf/syscall.c | 36 ++++++++++++++++++++--------------
> tools/include/uapi/linux/bpf.h | 2 ++
> 4 files changed, 47 insertions(+), 16 deletions(-)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 6498be4c44f8..d84af3719b59 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -3829,14 +3829,35 @@ bpf_prog_update_insn_ptrs(struct bpf_prog *prog, u32 *offsets, void *image)
> }
> #endif
>
> +static inline bool bpf_map_supports_cpu_flags(enum bpf_map_type map_type)
> +{
> + return false;
> +}
> +
> static inline int bpf_map_check_op_flags(struct bpf_map *map, u64 flags, u64 allowed_flags)
> {
> - if (flags & ~allowed_flags)
> + u32 cpu;
> +
> + if ((u32)flags & ~allowed_flags)
> 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)) {
> + if (!bpf_map_supports_cpu_flags(map->map_type))
> + return -EINVAL;
> + if ((flags & BPF_F_CPU) && (flags & BPF_F_ALL_CPUS))
> + return -EINVAL;
> +
> + cpu = flags >> 32;
> + if ((flags & BPF_F_CPU) && cpu >= num_possible_cpus())
> + return -ERANGE;
> + }
> +
> return 0;
> }
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index f5713f59ac10..8b6279ca6e66 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -1373,6 +1373,8 @@ 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, /* 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 */
> };
>
> /* flags for BPF_MAP_CREATE command */
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index cef8963d69f9..3c3e3b4095b9 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -133,12 +133,14 @@ 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)
> -{
> - 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)
> +static u32 bpf_map_value_size(const struct bpf_map *map, u64 flags)
> +{
> + if (flags & (BPF_F_CPU | BPF_F_ALL_CPUS))
> + return map->value_size;
> + 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)
> return round_up(map->value_size, 8) * num_possible_cpus();
> else if (IS_FD_MAP(map))
> return sizeof(u32);
> @@ -1732,7 +1734,7 @@ static int map_lookup_elem(union bpf_attr *attr)
> if (!(map_get_sys_perms(map, f) & FMODE_CAN_READ))
> return -EPERM;
>
> - err = bpf_map_check_op_flags(map, attr->flags, BPF_F_LOCK);
> + err = bpf_map_check_op_flags(map, attr->flags, BPF_F_LOCK | BPF_F_CPU);
> if (err)
> return err;
>
> @@ -1740,7 +1742,7 @@ 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);
> @@ -1781,6 +1783,7 @@ static int map_update_elem(union bpf_attr *attr, bpfptr_t uattr)
> bpfptr_t uvalue = make_bpfptr(attr->value, uattr.is_kernel);
> struct bpf_map *map;
> void *key, *value;
> + u64 allowed_flags;
> u32 value_size;
> int err;
>
> @@ -1797,7 +1800,8 @@ static int map_update_elem(union bpf_attr *attr, bpfptr_t uattr)
> goto err_put;
> }
>
> - err = bpf_map_check_op_flags(map, attr->flags, ~0);
> + allowed_flags = (BPF_F_ALL_CPUS << 1) - 1;
This is cryptic.
Use
allowed_flags = BPF_NOEXIST | BPF_EXIST | BPF_F_LOCK | BPF_F_CPU |
BPF_F_ALL_CPUS;
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