[PATCH 0/6] mm/hugetlb: More fixes around uffd-wp vs fork() / RO pins

[Peter Xu <peterx@redhat.com>]

This is a follow up of previous discussion here:

https://lore.kernel.org/r/20230324222707.GA3046@monkey

There, Mike correctly pointed out that uffd-wp bit can get lost too when
Copy-On-Read triggers.  Last time we didn't have a reproducer, I finally
wrote a reproducer and attached as the last patch.

When at it, I decided to also add some more uffd-wp tests against fork(),
and I found more bugs.  None of them were reported by anyone probably
because none of us cares, but since they're still bugs and can be
reproduced by the unit test I fixed them too in another patch.

The initial patch 1-2 are fixes to bugs, copied stable.

The rest patches 3-6 introduces unit tests to verify (based on the recent
rework on uffd unit test).  Note that not all the bugfixes in patch 1 is
verified (e.g. on changes to hugetlb hwpoison / migration entries), but I
assume they can be reviewed with careful eyes.

Thanks,

Peter Xu (6):
  mm/hugetlb: Fix uffd-wp during fork()
  mm/hugetlb: Fix uffd-wp bit lost when unsharing happens
  selftests/mm: Add a few options for uffd-unit-test
  selftests/mm: Extend and rename uffd pagemap test
  selftests/mm: Rename COW_EXTRA_LIBS to IOURING_EXTRA_LIBS
  selftests/mm: Add tests for RO pinning vs fork()

 mm/hugetlb.c                                 |  33 +-
 tools/testing/selftests/mm/Makefile          |   8 +-
 tools/testing/selftests/mm/check_config.sh   |   4 +-
 tools/testing/selftests/mm/uffd-unit-tests.c | 318 +++++++++++++++++--
 4 files changed, 315 insertions(+), 48 deletions(-)

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2.39.1