On Wed, Sep 3, 2025 at 10:36 AM Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> wrote: > > On Wed, Sep 3, 2025 at 10:04 AM Leon Hwang <leon.hwang@xxxxxxxxx> wrote: > > > > While adding support for the BPF_F_CPU and BPF_F_ALL_CPUS flags, the data > > copying logic of the following percpu map types needs to be updated: > > > > * percpu_array > > * percpu_hash > > * lru_percpu_hash > > * percpu_cgroup_storage > > > > Following Andrii’s suggestion[0], this patch refactors the data copying as flattering as that is, "Andrii's suggestion" is no justification why the patch is correct :) > > logic by introducing two helpers: > > > > * `bpf_percpu_copy_to_user()` > > * `bpf_percpu_copy_from_user()` > > > > This prepares the codebase for the upcoming CPU flag support. > > > > [0] https://lore.kernel.org/bpf/20250827164509.7401-1-leon.hwang@xxxxxxxxx/ > > > > Suggested-by: Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> > > Signed-off-by: Leon Hwang <leon.hwang@xxxxxxxxx> > > --- > > include/linux/bpf.h | 29 ++++++++++++++++++++++++++++- > > kernel/bpf/arraymap.c | 14 ++------------ > > kernel/bpf/hashtab.c | 20 +++----------------- > > kernel/bpf/local_storage.c | 18 ++++++------------ > > 4 files changed, 39 insertions(+), 42 deletions(-) > > > > diff --git a/include/linux/bpf.h b/include/linux/bpf.h > > index 8f6e87f0f3a89..2dc0299a2da50 100644 > > --- a/include/linux/bpf.h > > +++ b/include/linux/bpf.h > > @@ -547,6 +547,34 @@ static inline void copy_map_value_long(struct bpf_map *map, void *dst, void *src > > bpf_obj_memcpy(map->record, dst, src, map->value_size, true); > > } > > > > +#ifdef CONFIG_BPF_SYSCALL > > +static inline void bpf_percpu_copy_to_user(struct bpf_map *map, void __percpu *pptr, void *value, > > + u32 size) > > +{ > > + int cpu, off = 0; > > + > > + 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); I still maintain that this makes zero sense... value+off is memory that we'll copy_to_user, why are we setting refcount to 1, or rb_node/list_node to "proper empty node" is absolutely not clear... it feels like we can drop check_and_init_map_value() altogether and be absolutely no worse. If anything, memset(0) would be nicer, but I guess we didn't have it to begin with, so no need to add it now. > > + off += size; > > + } > > +} > > + > > +void bpf_obj_free_fields(const struct btf_record *rec, void *obj); > > + > > +static inline void bpf_percpu_copy_from_user(struct bpf_map *map, void __percpu *pptr, void *value, > > + u32 size) > > +{ > > + int cpu, off = 0; > > + > > + for_each_possible_cpu(cpu) { > > + copy_map_value_long(map, per_cpu_ptr(pptr, cpu), value + off); copy_map_value_long is generalization of bpf_long_memcpy, and so it would be good to call this out to explain why your refactoring is correct > > + bpf_obj_free_fields(map->record, per_cpu_ptr(pptr, cpu)); > > + off += size; > > + } > > +} > > +#endif > > + > > static inline void bpf_obj_swap_uptrs(const struct btf_record *rec, void *dst, void *src) > > { > > unsigned long *src_uptr, *dst_uptr; > > @@ -2417,7 +2445,6 @@ struct btf_record *btf_record_dup(const struct btf_record *rec); > > bool btf_record_equal(const struct btf_record *rec_a, const struct btf_record *rec_b); > > void bpf_obj_free_timer(const struct btf_record *rec, void *obj); > > void bpf_obj_free_workqueue(const struct btf_record *rec, void *obj); > > -void bpf_obj_free_fields(const struct btf_record *rec, void *obj); > > void __bpf_obj_drop_impl(void *p, const struct btf_record *rec, bool percpu); > > > > struct bpf_map *bpf_map_get(u32 ufd); > > diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c > > index 3d080916faf97..6be9c54604503 100644 > > --- a/kernel/bpf/arraymap.c > > +++ b/kernel/bpf/arraymap.c > > @@ -300,7 +300,6 @@ int bpf_percpu_array_copy(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; > > > > if (unlikely(index >= array->map.max_entries)) > > @@ -313,11 +312,7 @@ 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; > > - } > > + bpf_percpu_copy_to_user(map, pptr, value, size); > > rcu_read_unlock(); > > return 0; > > } > > @@ -387,7 +382,6 @@ 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; > > > > if (unlikely(map_flags > BPF_EXIST)) > > @@ -411,11 +405,7 @@ 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); > > - bpf_obj_free_fields(array->map.record, per_cpu_ptr(pptr, cpu)); > > - off += size; > > - } > > + bpf_percpu_copy_from_user(map, pptr, value, size); > > rcu_read_unlock(); > > return 0; > > } > > diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c > > index 71f9931ac64cd..5f0f3c00dbb74 100644 > > --- a/kernel/bpf/hashtab.c > > +++ b/kernel/bpf/hashtab.c > > @@ -944,12 +944,8 @@ static void pcpu_copy_value(struct bpf_htab *htab, void __percpu *pptr, > > copy_map_value(&htab->map, this_cpu_ptr(pptr), value); > > } else { > > u32 size = round_up(htab->map.value_size, 8); > > - int off = 0, cpu; > > > > - for_each_possible_cpu(cpu) { > > - copy_map_value_long(&htab->map, per_cpu_ptr(pptr, cpu), value + off); > > - off += size; > > - } > > + bpf_percpu_copy_from_user(&htab->map, pptr, value, size); > > This is not a refactor. There is a significant change in the logic. > Why is it needed? Bug fix or introducing a bug? this is preparation for that BPF_F_CPU/BPF_F_ALLCPUS, but I agree that it would be better to include as preparatory patch in the actual patch set > > The names to_user and from_user are wrong. > There is no user space memory involved. This was my suggestion because we either are copying user-supplied data or copying data back to user. Strictly speaking it's all kernel memory (copy_from_user/copy_to_user is done afterwards by the caller), but that's the intent. Maybe "copy_in" and "copy_out" would be better, I don't know. But there is certainly a direction here w.r.t. user space provided data (note, this is not BPF program-side logic). > > pw-bot: cr
