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Message-ID: <20251117162033.6296-1-leon.hwang@linux.dev>
Date: Tue, 18 Nov 2025 00:20:25 +0800
From: Leon Hwang <leon.hwang@...ux.dev>
To: bpf@...r.kernel.org
Cc: ast@...nel.org,
andrii@...nel.org,
daniel@...earbox.net,
jolsa@...nel.org,
yonghong.song@...ux.dev,
song@...nel.org,
eddyz87@...il.com,
dxu@...uu.xyz,
deso@...teo.net,
martin.lau@...ux.dev,
john.fastabend@...il.com,
kpsingh@...nel.org,
sdf@...ichev.me,
haoluo@...gle.com,
shuah@...nel.org,
kerneljasonxing@...il.com,
chen.dylane@...ux.dev,
willemb@...gle.com,
paul.chaignon@...il.com,
a.s.protopopov@...il.com,
memxor@...il.com,
yatsenko@...a.com,
tklauser@...tanz.ch,
leon.hwang@...ux.dev,
kernel-patches-bot@...com,
linux-kernel@...r.kernel.org,
linux-kselftest@...r.kernel.org
Subject: [PATCH bpf-next v10 0/8] bpf: Introduce BPF_F_CPU and BPF_F_ALL_CPUS flags for percpu maps
This patch set introduces the BPF_F_CPU and BPF_F_ALL_CPUS flags for
percpu maps, as the requirement of BPF_F_ALL_CPUS flag for percpu_array
maps was discussed in the thread of
"[PATCH bpf-next v3 0/4] bpf: Introduce global percpu data"[1].
The goal of BPF_F_ALL_CPUS flag is to reduce data caching overhead in light
skeletons by allowing a single value to be reused to update values across all
CPUs. This avoids the M:N problem where M cached values are used to update a
map on N CPUs kernel.
The BPF_F_CPU flag is accompanied by *flags*-embedded cpu info, which
specifies the target CPU for the operation:
* For lookup operations: the flag field alongside cpu info enable querying
a value on the specified CPU.
* For update operations: the flag field alongside cpu info enable
updating value for specified CPU.
Links:
[1] https://lore.kernel.org/bpf/20250526162146.24429-1-leon.hwang@linux.dev/
Changes:
v9 -> v10:
* Add tests to verify array and hash maps do not support BPF_F_CPU and
BPF_F_ALL_CPUS flags.
* Address comment from Andrii:
* Copy map value using copy_map_value_long for percpu_cgroup_storage
maps in a separate patch.
v8 -> v9:
* Change value type from u64 to u32 in selftests.
* Address comments from Andrii:
* Keep value_size unaligned and update everywhere for consistency when
cpu flags are specified.
* Update value by getting pointer for percpu hash and percpu
cgroup_storage maps.
v7 -> v8:
* Address comments from Andrii:
* Check BPF_F_LOCK when update percpu_array, percpu_hash and
lru_percpu_hash maps.
* Refactor flags check in __htab_map_lookup_and_delete_batch().
* Keep value_size unaligned and copy value using copy_map_value() in
__htab_map_lookup_and_delete_batch() when BPF_F_CPU is specified.
* Update warn message in libbpf's validate_map_op().
* Update comment of libbpf's bpf_map__lookup_elem().
v6 -> v7:
* Get correct value size for percpu_hash and lru_percpu_hash in
update_batch API.
* Set 'count' as 'max_entries' in test cases for lookup_batch API.
* Address comment from Alexei:
* Move cpu flags check into bpf_map_check_op_flags().
v5 -> v6:
* Move bpf_map_check_op_flags() from 'bpf.h' to 'syscall.c'.
* Address comments from Alexei:
* Drop the refactoring code of data copying logic for percpu maps.
* Drop bpf_map_check_op_flags() wrappers.
v4 -> v5:
* Address comments from Andrii:
* Refactor data copying logic for all percpu maps.
* Drop this_cpu_ptr() micro-optimization.
* Drop cpu check in libbpf's validate_map_op().
* Enhance bpf_map_check_op_flags() using *allowed flags* instead of
'extra_flags_mask'.
v3 -> v4:
* Address comments from Andrii:
* Remove unnecessary map_type check in bpf_map_value_size().
* Reduce code churn.
* Remove unnecessary do_delete check in
__htab_map_lookup_and_delete_batch().
* Introduce bpf_percpu_copy_to_user() and bpf_percpu_copy_from_user().
* Rename check_map_flags() to bpf_map_check_op_flags() with
extra_flags_mask.
* Add human-readable pr_warn() explanations in validate_map_op().
* Use flags in bpf_map__delete_elem() and
bpf_map__lookup_and_delete_elem().
* Drop "for alignment reasons".
v3 link: https://lore.kernel.org/bpf/20250821160817.70285-1-leon.hwang@linux.dev/
v2 -> v3:
* Address comments from Alexei:
* Use BPF_F_ALL_CPUS instead of BPF_ALL_CPUS magic.
* Introduce these two cpu flags for all percpu maps.
* Address comments from Jiri:
* Reduce some unnecessary u32 cast.
* Refactor more generic map flags check function.
* A code style issue.
v2 link: https://lore.kernel.org/bpf/20250805163017.17015-1-leon.hwang@linux.dev/
v1 -> v2:
* Address comments from Andrii:
* Embed cpu info as high 32 bits of *flags* totally.
* Use ERANGE instead of E2BIG.
* Few format issues.
Leon Hwang (8):
bpf: Introduce internal bpf_map_check_op_flags helper function
bpf: Introduce BPF_F_CPU and BPF_F_ALL_CPUS flags
bpf: Add BPF_F_CPU and BPF_F_ALL_CPUS flags support for percpu_array
maps
bpf: Add BPF_F_CPU and BPF_F_ALL_CPUS flags support for percpu_hash
and lru_percpu_hash maps
bpf: Copy map value using copy_map_value_long for
percpu_cgroup_storage maps
bpf: Add BPF_F_CPU and BPF_F_ALL_CPUS flags support for
percpu_cgroup_storage maps
libbpf: Add BPF_F_CPU and BPF_F_ALL_CPUS flags support for percpu maps
selftests/bpf: Add cases to test BPF_F_CPU and BPF_F_ALL_CPUS flags
include/linux/bpf-cgroup.h | 4 +-
include/linux/bpf.h | 44 ++-
include/uapi/linux/bpf.h | 2 +
kernel/bpf/arraymap.c | 29 +-
kernel/bpf/hashtab.c | 94 ++++--
kernel/bpf/local_storage.c | 27 +-
kernel/bpf/syscall.c | 65 ++--
tools/include/uapi/linux/bpf.h | 2 +
tools/lib/bpf/bpf.h | 8 +
tools/lib/bpf/libbpf.c | 26 +-
tools/lib/bpf/libbpf.h | 21 +-
.../selftests/bpf/prog_tests/percpu_alloc.c | 312 ++++++++++++++++++
.../selftests/bpf/progs/percpu_alloc_array.c | 32 ++
13 files changed, 562 insertions(+), 104 deletions(-)
--
2.51.2
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