[PATCH v2 0/4] cgroup: dmem: add selftest helper, coverage, and VM runner

[Albert Esteve <aesteve@redhat.com>]

Hi all,

This small series adds practical test coverage for the dmem
cgroup controller.

The motivation came from following the recent dmem API discussion in
thread [1]. That discussion considered changing the dmem API and
adding a new knob. Currently there are no dedicated tests covering
dmem behaviour, which makes such changes riskier.

Adding selftests has an additional challenge: dmem charging paths
are driver-driven today, so regression testing is harder unless a
suitable driver is present in the test environment.

This series addresses that by adding:
- a kernel-side selftest helper module to trigger charge/uncharge
  from userspace in a controlled way,
- cgroup selftests covering dmem accounting and protection semantics
  (including dmem.max enforcement and byte-granularity checks),
- a virtme-based VM runner for repeatable execution of the dmem tests.

The goal is to make dmem behavior easier to validate when evolving the API
and implementation, while keeping tests deterministic and driver-independent.

Thanks.

[1] - https://lore.kernel.org/all/aZoHfloupKvF2oSu@fedora/

Signed-off-by: Albert Esteve <aesteve@redhat.com>
---
Changes in v2:
- Fix debugfs_create_dir() error check
- Fix module teardown race: call dmem_selftest_remove() before
  uncharging so debugfs files are torn down
- Use IS_ERR_OR_NULL() in selftest() sanity check
- Add CONFIG_CGROUP_DMEM=y to the cgroup selftest config
- Replace config-file parsing in check_guest_requirements() with
  a direct check of /sys/fs/cgroup/cgroup.controllers
- Add new patch 4 (from Eric Chanudet): vmtest-dmem.sh -b flag
  to configure and build a local kernel tree
- Link to v1: https://lore.kernel.org/r/20260327-kunit_cgroups-v1-0-971b3c739a00@redhat.com

---
Albert Esteve (3):
      cgroup: Add dmem_selftest module
      selftests: cgroup: Add dmem selftest coverage
      selftests: cgroup: Add vmtest-dmem runner based on hid vmtest

Eric Chanudet (1):
      selftests: cgroup: handle vmtest-dmem -b to test locally built kernel

 init/Kconfig                                  |  12 +
 kernel/cgroup/Makefile                        |   1 +
 kernel/cgroup/dmem_selftest.c                 | 198 +++++++++++
 tools/testing/selftests/cgroup/.gitignore     |   1 +
 tools/testing/selftests/cgroup/Makefile       |   2 +
 tools/testing/selftests/cgroup/config         |   1 +
 tools/testing/selftests/cgroup/test_dmem.c    | 490 ++++++++++++++++++++++++++
 tools/testing/selftests/cgroup/vmtest-dmem.sh | 229 ++++++++++++
 8 files changed, 934 insertions(+)
---
base-commit: 80234b5ab240f52fa45d201e899e207b9265ef91
change-id: 20260318-kunit_cgroups-7fb0b9e64017

Best regards,
-- 
Albert Esteve <aesteve@redhat.com>