[v2,0/2] bpf: introduce helper for populating bpf_cpumask

Message

Emil Tsalapatis March 5, 2025, 2:10 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 :
-----------
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 (2):
  bpf: add kfunc for populating cpumask bits
  selftests: bpf: add bpf_cpumask_fill selftests

 kernel/bpf/cpumask.c                          |  27 +++++
 .../selftests/bpf/prog_tests/cpumask.c        |   3 +
 .../selftests/bpf/progs/cpumask_failure.c     |  38 ++++++
 .../selftests/bpf/progs/cpumask_success.c     | 109 ++++++++++++++++++
 4 files changed, 177 insertions(+)