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@linux.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@kernel.org Signed-off-by: Leon Hwang leon.hwang@linux.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;