I really don't think this approach is any good. You workaround
a deficiency in the pin_user_pages API in one particular caller for
one particular use case.
I think you'd rather want either:
(1) a FOLL_HUGEPAGE flag for the pin_user_pages API family that returns
a single struct page for any kind of huge page, which would also
benefit all kinds of other users rather than adding these kinds of
hacks to vfio.
(2) add a bvec version of the API that returns a variable size
"extent"
I had started on (2) a while ago, and here is branch with my code (which
is broken and fails test, but might be a start):
http://git.infradead.org/users/hch/misc.git/shortlog/refs/heads/gup-bvec
But for now I wonder if (1) is the better start, which could still be
reused to (2) later.
