selftests/vm: use memfd for uffd hugetlb tests

Patch series "selftests/vm: Drop hugetlb mntpoint in run_vmtests.sh", v2.

Clean the code up so we can use the same memfd for both hugetlb and shmem
which is cleaner.


This patch (of 4):

We already used memfd for shmem test, move it forward with hugetlb too so
that we don't need user to specify the hugetlb file path explicitly when
running hugetlb shared tests.

Link: https://lkml.kernel.org/r/20221014143921.93887-1-peterx@redhat.com
Link: https://lkml.kernel.org/r/20221014143921.93887-2-peterx@redhat.com


Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Axel Rasmussen <axelrasmussen@google.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>