drm/etnaviv: User FOLL_LONGTERM in userptr

There's no mmu notifier or anything like that, releasing this pin is
entirely up to userspace. Hence FOLL_LONGTERM.

No cc: stable for this patch since a lot of the infrastructure around
FOLL_LONGETRM (like not allowing it for pages currently sitting in
ZONE_MOVEABLE before they're migrated) is still being worked on. So
not big benefits yet.
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Lucas Stach <l.stach@pengutronix.de>
Cc: Russell King <linux+etnaviv@armlinux.org.uk>
Cc: Christian Gmeiner <christian.gmeiner@gmail.com>
Cc: etnaviv@lists.freedesktop.org
Link: https://patchwork.freedesktop.org/patch/msgid/20210301095254.1946084-2-daniel.vetter@ffwll.ch

drivers/gpu/drm/etnaviv/etnaviv_gem.c

@@ -689,7 +689,8 @@ static int etnaviv_gem_userptr_get_pages(struct etnaviv_gem_object *etnaviv_obj)
 		struct page **pages = pvec + pinned;
 
 		ret = pin_user_pages_fast(ptr, num_pages,
-					  FOLL_WRITE | FOLL_FORCE, pages);
+					  FOLL_WRITE | FOLL_FORCE | FOLL_LONGTERM,
+					  pages);
 		if (ret < 0) {
 			unpin_user_pages(pvec, pinned);
 			kvfree(pvec);