net/xdp: set FOLL_PIN via pin_user_pages()

Convert net/xdp to use the new pin_longterm_pages() call, which sets
FOLL_PIN.  Setting FOLL_PIN is now required for code that requires
tracking of pinned pages.

In partial anticipation of this work, the net/xdp code was already calling
put_user_page() instead of put_page().  Therefore, in order to convert
from the get_user_pages()/put_page() model, to the
pin_user_pages()/put_user_page() model, the only change required here is
to change get_user_pages() to pin_user_pages().

Link: http://lkml.kernel.org/r/20200107224558.2362728-18-jhubbard@nvidia.com
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Acked-by: Björn Töpel <bjorn.topel@intel.com>
Cc: Alex Williamson <alex.williamson@redhat.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jason Gunthorpe <jgg@mellanox.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Leon Romanovsky <leonro@mellanox.com>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

net/xdp/xdp_umem.c

@@ -291,7 +291,7 @@ static int xdp_umem_pin_pages(struct xdp_umem *umem)
 		return -ENOMEM;
 
 	down_read(&current->mm->mmap_sem);
-	npgs = get_user_pages(umem->address, umem->npgs,
+	npgs = pin_user_pages(umem->address, umem->npgs,
 			      gup_flags | FOLL_LONGTERM, &umem->pgs[0], NULL);
 	up_read(&current->mm->mmap_sem);