Merge branch 'bpf-introduce-helper-for-populating-bpf_cpumask'

Emil Tsalapatis says:

====================
bpf: introduce helper for populating bpf_cpumask

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 :
-----------
v6->v7
v6:https://lore.kernel.org/bpf/20250307153847.8530-1-emil@etsalapatis.com/

Addressed feedback by Hou Tao:
	* Removed RUN_TESTS invocation causing tests to run twice
	* Added is_test_task guard to new selftests
	* Removed extraneous __success attribute from existing selftests

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>
====================

Link: https://patch.msgid.link/20250309230427.26603-1-emil@etsalapatis.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>