selftests: prctl: introduce tests for disabling THPs except for madvise

The test will set the global system THP setting to never, madvise or
always depending on the fixture variant and the 2M setting to inherit
before it starts (and reset to original at teardown).  The fixture setup
will also test if PR_SET_THP_DISABLE prctl call can be made with
PR_THP_DISABLE_EXCEPT_ADVISED and skip if it fails.

This tests if the process can:
- successfully get the policy to disable THPs expect for madvise.
- get hugepages only on MADV_HUGE and MADV_COLLAPSE if the global policy
  is madvise/always and only with MADV_COLLAPSE if the global policy is
  never.
- successfully reset the policy of the process.
- after reset, only get hugepages with:
  - MADV_COLLAPSE when policy is set to never.
  - MADV_HUGE and MADV_COLLAPSE when policy is set to madvise.
  - always when policy is set to "always".
- never get a THP with MADV_NOHUGEPAGE.
- repeat the above tests in a forked process to make sure  the policy is
  carried across forks.

Test results:
./prctl_thp_disable
TAP version 13
1..12
ok 1 prctl_thp_disable_completely.never.nofork
ok 2 prctl_thp_disable_completely.never.fork
ok 3 prctl_thp_disable_completely.madvise.nofork
ok 4 prctl_thp_disable_completely.madvise.fork
ok 5 prctl_thp_disable_completely.always.nofork
ok 6 prctl_thp_disable_completely.always.fork
ok 7 prctl_thp_disable_except_madvise.never.nofork
ok 8 prctl_thp_disable_except_madvise.never.fork
ok 9 prctl_thp_disable_except_madvise.madvise.nofork
ok 10 prctl_thp_disable_except_madvise.madvise.fork
ok 11 prctl_thp_disable_except_madvise.always.nofork
ok 12 prctl_thp_disable_except_madvise.always.fork

[usamaarif642@gmail.com: return after executing test in child process]
  Link: https://lkml.kernel.org/r/3dca2de4-9a6a-4efe-a86c-83f9509831fc@gmail.com
Link: https://lkml.kernel.org/r/20250815135549.130506-8-usamaarif642@gmail.com
Signed-off-by: Usama Arif <usamaarif642@gmail.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Jann Horn <jannh@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Mariano Pache <npache@redhat.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: SeongJae Park <sj@kernel.org>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Yafang <laoar.shao@gmail.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

0 files changed, 0 insertions, 0 deletions