selftests/mm: introduce uffd-wp-mremap regression test

Introduce a test that registers a range of memory for
UFFDIO_WRITEPROTECT_MODE_WP without UFFD_FEATURE_EVENT_REMAP.  First check
that the uffd-wp bit is set for every PTE in the range.  Then mremap() the
range to a new location and check that the uffd-wp bit is clear for every
PTE in the range.

Run the test for small folios, all supported THP sizes and all supported
hugetlb sizes, and for swapped out memory, shared and private.

There was previously a bug in the kernel where the uffd-wp bits remained
set in all PTEs for this case, after fixing the kernel, the tests all
pass.

Link: https://lkml.kernel.org/r/20250107144755.1871363-3-ryan.roberts@arm.com


Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: Liam R. Howlett <Liam.Howlett@Oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Peter Xu <peterx@redhat.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>