This is necessary to prevent races with invalidation. It is currently
possible that page tables are garbage collected while paging caches
refer to them. We must ensure that pages are held until caches can be
invalidated. This is not achieved by this goal alone, but moving locking
to outside the page tables themselves is a requisite.
PiperOrigin-RevId: 198920784
Change-Id: I66fffecd49cb14aa2e676a84a68cabfc0c8b3e9a