Patch series "selftests/mm: new test for FOLL_LONGTERM on file mappings".

Let's add some selftests to make sure that:
* R/O long-term pinning always works of file mappings
* R/W long-term pinning always works in MAP_PRIVATE file mappings
* R/W long-term pinning only works in MAP_SHARED mappings with special
  filesystems (shmem, hugetlb) and fails with other filesystems (ext4, btrfs,
  xfs).

The tests make use of the gup_test kernel module to trigger ordinary GUP
and GUP-fast, and liburing (similar to our COW selftests).  Test with
memfd, memfd hugetlb, tmpfile() and mkstemp().  The latter usually gives
us a "real" filesystem (ext4, btrfs, xfs) where long-term pinning is
expected to fail.

Note that these selftests don't contain any actual reproducers for data
corruptions in case R/W long-term pinning on problematic filesystems
"would" work.

Maybe we can later come up with a racy !FOLL_LONGTERM reproducer that can
reuse an existing interface to trigger short-term pinning (I'll look into
that next).

On current mm/mm-unstable:
	# ./gup_longterm
	# [INFO] detected hugetlb page size: 2048 KiB
	# [INFO] detected hugetlb page size: 1048576 KiB
	TAP version 13
	1..50
	# [RUN] R/W longterm GUP pin in MAP_SHARED file mapping ... with memfd
	ok 1 Should have worked
	# [RUN] R/W longterm GUP pin in MAP_SHARED file mapping ... with tmpfile
	ok 2 Should have worked
	# [RUN] R/W longterm GUP pin in MAP_SHARED file mapping ... with local tmpfile
	ok 3 Should have failed
	# [RUN] R/W longterm GUP pin in MAP_SHARED file mapping ... with memfd hugetlb (2048 kB)
	ok 4 Should have worked
	# [RUN] R/W longterm GUP pin in MAP_SHARED file mapping ... with memfd hugetlb (1048576 kB)
	ok 5 Should have worked
	# [RUN] R/W longterm GUP-fast pin in MAP_SHARED file mapping ... with memfd
	ok 6 Should have worked
	# [RUN] R/W longterm GUP-fast pin in MAP_SHARED file mapping ... with tmpfile
	ok 7 Should have worked
	# [RUN] R/W longterm GUP-fast pin in MAP_SHARED file mapping ... with local tmpfile
	ok 8 Should have failed
	# [RUN] R/W longterm GUP-fast pin in MAP_SHARED file mapping ... with memfd hugetlb (2048 kB)
	ok 9 Should have worked
	# [RUN] R/W longterm GUP-fast pin in MAP_SHARED file mapping ... with memfd hugetlb (1048576 kB)
	ok 10 Should have worked
	# [RUN] R/O longterm GUP pin in MAP_SHARED file mapping ... with memfd
	ok 11 Should have worked
	# [RUN] R/O longterm GUP pin in MAP_SHARED file mapping ... with tmpfile
	ok 12 Should have worked
	# [RUN] R/O longterm GUP pin in MAP_SHARED file mapping ... with local tmpfile
	ok 13 Should have worked
	# [RUN] R/O longterm GUP pin in MAP_SHARED file mapping ... with memfd hugetlb (2048 kB)
	ok 14 Should have worked
	# [RUN] R/O longterm GUP pin in MAP_SHARED file mapping ... with memfd hugetlb (1048576 kB)
	ok 15 Should have worked
	# [RUN] R/O longterm GUP-fast pin in MAP_SHARED file mapping ... with memfd
	ok 16 Should have worked
	# [RUN] R/O longterm GUP-fast pin in MAP_SHARED file mapping ... with tmpfile
	ok 17 Should have worked
	# [RUN] R/O longterm GUP-fast pin in MAP_SHARED file mapping ... with local tmpfile
	ok 18 Should have worked
	# [RUN] R/O longterm GUP-fast pin in MAP_SHARED file mapping ... with memfd hugetlb (2048 kB)
	ok 19 Should have worked
	# [RUN] R/O longterm GUP-fast pin in MAP_SHARED file mapping ... with memfd hugetlb (1048576 kB)
	ok 20 Should have worked
	# [RUN] R/W longterm GUP pin in MAP_PRIVATE file mapping ... with memfd
	ok 21 Should have worked
	# [RUN] R/W longterm GUP pin in MAP_PRIVATE file mapping ... with tmpfile
	ok 22 Should have worked
	# [RUN] R/W longterm GUP pin in MAP_PRIVATE file mapping ... with local tmpfile
	ok 23 Should have worked
	# [RUN] R/W longterm GUP pin in MAP_PRIVATE file mapping ... with memfd hugetlb (2048 kB)
	ok 24 Should have worked
	# [RUN] R/W longterm GUP pin in MAP_PRIVATE file mapping ... with memfd hugetlb (1048576 kB)
	ok 25 Should have worked
	# [RUN] R/W longterm GUP-fast pin in MAP_PRIVATE file mapping ... with memfd
	ok 26 Should have worked
	# [RUN] R/W longterm GUP-fast pin in MAP_PRIVATE file mapping ... with tmpfile
	ok 27 Should have worked
	# [RUN] R/W longterm GUP-fast pin in MAP_PRIVATE file mapping ... with local tmpfile
	ok 28 Should have worked
	# [RUN] R/W longterm GUP-fast pin in MAP_PRIVATE file mapping ... with memfd hugetlb (2048 kB)
	ok 29 Should have worked
	# [RUN] R/W longterm GUP-fast pin in MAP_PRIVATE file mapping ... with memfd hugetlb (1048576 kB)
	ok 30 Should have worked
	# [RUN] R/O longterm GUP pin in MAP_PRIVATE file mapping ... with memfd
	ok 31 Should have worked
	# [RUN] R/O longterm GUP pin in MAP_PRIVATE file mapping ... with tmpfile
	ok 32 Should have worked
	# [RUN] R/O longterm GUP pin in MAP_PRIVATE file mapping ... with local tmpfile
	ok 33 Should have worked
	# [RUN] R/O longterm GUP pin in MAP_PRIVATE file mapping ... with memfd hugetlb (2048 kB)
	ok 34 Should have worked
	# [RUN] R/O longterm GUP pin in MAP_PRIVATE file mapping ... with memfd hugetlb (1048576 kB)
	ok 35 Should have worked
	# [RUN] R/O longterm GUP-fast pin in MAP_PRIVATE file mapping ... with memfd
	ok 36 Should have worked
	# [RUN] R/O longterm GUP-fast pin in MAP_PRIVATE file mapping ... with tmpfile
	ok 37 Should have worked
	# [RUN] R/O longterm GUP-fast pin in MAP_PRIVATE file mapping ... with local tmpfile
	ok 38 Should have worked
	# [RUN] R/O longterm GUP-fast pin in MAP_PRIVATE file mapping ... with memfd hugetlb (2048 kB)
	ok 39 Should have worked
	# [RUN] R/O longterm GUP-fast pin in MAP_PRIVATE file mapping ... with memfd hugetlb (1048576 kB)
	ok 40 Should have worked
	# [RUN] io_uring fixed buffer with MAP_SHARED file mapping ... with memfd
	ok 41 Should have worked
	# [RUN] io_uring fixed buffer with MAP_SHARED file mapping ... with tmpfile
	ok 42 Should have worked
	# [RUN] io_uring fixed buffer with MAP_SHARED file mapping ... with local tmpfile
	ok 43 Should have failed
	# [RUN] io_uring fixed buffer with MAP_SHARED file mapping ... with memfd hugetlb (2048 kB)
	ok 44 Should have worked
	# [RUN] io_uring fixed buffer with MAP_SHARED file mapping ... with memfd hugetlb (1048576 kB)
	ok 45 Should have worked
	# [RUN] io_uring fixed buffer with MAP_PRIVATE file mapping ... with memfd
	ok 46 Should have worked
	# [RUN] io_uring fixed buffer with MAP_PRIVATE file mapping ... with tmpfile
	ok 47 Should have worked
	# [RUN] io_uring fixed buffer with MAP_PRIVATE file mapping ... with local tmpfile
	ok 48 Should have worked
	# [RUN] io_uring fixed buffer with MAP_PRIVATE file mapping ... with memfd hugetlb (2048 kB)
	ok 49 Should have worked
	# [RUN] io_uring fixed buffer with MAP_PRIVATE file mapping ... with memfd hugetlb (1048576 kB)
	ok 50 Should have worked
	# Totals: pass:50 fail:0 xfail:0 xpass:0 skip:0 error:0


This patch (of 3):

Let's factor detection out into vm_util, to be reused by a new test.

Link: https://lkml.kernel.org/r/20230519102723.185721-1-david@redhat.com
Link: https://lkml.kernel.org/r/20230519102723.185721-2-david@redhat.comSigned-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>