mm: don't call vm_ops->huge_fault() in wp_huge_pmd()/wp_huge_pud() for private mappings

If we already have a PMD/PUD mapped write-protected in a private mapping
and we want to break COW either due to FAULT_FLAG_WRITE or
FAULT_FLAG_UNSHARE, there is no need to inform the file system just like on
the PTE path.

Let's just split (->zap) + fallback in that case.

This is a preparation for more generic FAULT_FLAG_UNSHARE support in
COW mappings.

Link: https://lkml.kernel.org/r/20221116102659.70287-8-david@redhat.com


Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>