On 4/9/25 07:39, Andrii Nakryiko wrote: > 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. > Agreed. As 'copy_map_value_long()' won't copy those fields, 'check_and_init_map_value()' is unnecessary here. >>> + 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 > No. It shouldn't call bpf_long_memcpy() before bpf_obj_free_fields(), or it will overwrite those fields data used for bpf_obj_free_fields(). It would be better to call bpf_obj_free_fields() then bpf_long_memcpy(). >>> + 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 > Ack. I'll move this patch into the patch set of BPF_F_CPU/BPF_F_ALLCPUS flags. >> >> 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). > 'bpf_percpu_copy_data()' and 'bpf_percpu_update_data()' would be better, as "copy_data" is used in those 'bpf_percpu_*_copy()' functions and "update_data" is used in those 'bpf_percpu_*_update()' functions. Thanks, Leon
