Re: [PATCH v1] mm/gup: disallow FOLL_FORCE|FOLL_WRITE on hugetlb mappings

[Jason Gunthorpe]

On Mon, Oct 31, 2022 at 04:25:24PM +0100, David Hildenbrand wrote:
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> Cc: Peter Xu <peterx@xxxxxxxxxx>
> Cc: John Hubbard <jhubbard@xxxxxxxxxx>
> Cc: Jason Gunthorpe <jgg@xxxxxxxxxx>
> Reported-by: syzbot+f0b97304ef90f0d0b1dc@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
> ---
> 
> I assume this has been broken at least since 2014, when mm/gup.c came to
> life. I failed to come up with a suitable Fixes tag quickly.

I'm worried this would break RDMA over hugetlbfs maps - which is a
real thing people do.

MikeK do you have test cases?

Jason