[PATCH v6 0/4] bpf: introduce helper for populating bpf_cpumask

Emil Tsalapatis
2025-03-07T15:38:52Z

Some BPF programs like scx schedulers have their own internal CPU mask types,
mask types, which they must transform into struct bpf_cpumask instances
before passing them to scheduling-related kfuncs. There is currently no
way to efficiently populate the bitfield of a bpf_cpumask from BPF memory,
and programs must use multiple bpf_cpumask_[set, clear] calls to do so.
Introduce a kfunc helper to populate the bitfield of a bpf_cpumask from valid
BPF memory with a single call.

Changelog :
-----------
v5->v6
v5:https://lore.kernel.org/bpf/20250307041738.6665-1-emil@etsalapatis.com/

Addressed feedback by Hou Tao:
* Removed __success attributes from cpumask selftests
* Fixed stale patch description that used old function name

v4->v5
v4: https://lore.kernel.org/bpf/20250305211235.368399-1-emil@etsalapatis.com/

Addressed feedback by Hou Tao:
* Readded the tests in tools/selftests/bpf/prog_tests/cpumask.c,
turns out the selftest entries were not duplicates.
* Removed stray whitespace in selftest.
* Add patch the missing selftest to prog_tests/cpumask.c
* Explicitly annotate all cpumask selftests with __success

The last patch could very well be its own cleanup patch, but I rolled it into
this series because it came up in the discussion. If the last patch in the
series has any issues I'd be fine with applying the first 3 patches and dealing
with it separately.

v3->v4
v3: https://lore.kernel.org/bpf/20250305161327.203396-1-emil@etsalapatis.com/

* Removed new tests from tools/selftests/bpf/prog_tests/cpumask.c because
they were being run twice.

Addressed feedback by Alexei Starovoitov:
* Added missing return value in function kdoc
* Added an additional patch fixing some missing kdoc fields in
kernel/bpf/cpumask.c

Addressed feedback by Tejun Heo:
* Renamed the kfunc to bpf_cpumask_populate to avoid confusion
w/ bitmap_fill()

v2->v3
v2: https://lore.kernel.org/bpf/20250305021020.1004858-1-emil@etsalapatis.com/

Addressed feedback by Alexei Starovoitov:
* Added back patch descriptions dropped from v1->v2
* Elide the alignment check for archs with efficient
unaligned accesses

v1->v2
v1: https://lore.kernel.org/bpf/20250228003321.1409285-1-emil@etsalapatis.com/

Addressed feedback by Hou Tao:
* Add check that the input buffer is aligned to sizeof(long)
* Adjust input buffer size check to use bitmap_size()
* Add selftest for checking the bit pattern of the bpf_cpumask
* Moved all selftests into existing files

Signed-off-by: Emil Tsalapatis (Meta) <emil@etsalapatis.com>

Emil Tsalapatis (4):
bpf: add kfunc for populating cpumask bits
selftests: bpf: add bpf_cpumask_populate selftests
bpf: fix missing kdoc string fields in cpumask.c
selftests: bpf: add cpumask test_refcount_null_tracking test to runner

kernel/bpf/cpumask.c | 53 +++++++++
.../selftests/bpf/prog_tests/cpumask.c | 4 +
.../selftests/bpf/progs/cpumask_common.h | 1 +
.../selftests/bpf/progs/cpumask_failure.c | 38 ++++++
.../selftests/bpf/progs/cpumask_success.c | 110 ++++++++++++++++++
5 files changed, 206 insertions(+)

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2.47.1