Re: [PATCH V4 1/2] vfio dma_map/unmap: optimized for hugetlbfs pages

[Christoph Hellwig]

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.