[v5,0/4] bpf: introduce helper for populating bpf_cpumask

Message

Emil Tsalapatis March 7, 2025, 4:17 a.m. UTC

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 :
-----------
v4->v5
v4: https://lore.kernel.org/bpf/[e-mail]/

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/[e-mail]/

	* 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/[e-mail]/

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/[e-mail]/

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) <[e-mail]>

Emil Tsalapatis (4):
  bpf: add kfunc for populating cpumask bits
  selftests: bpf: add bpf_cpumask_fill selftests
  bpf: fix missing kdoc string fields in cpumask.c
  selftests: bpf: add missing cpumask test to runner and annotate
    existing tests

 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     | 131 ++++++++++++++++++
 5 files changed, 227 insertions(+)