drm/etnaviv: remove FOLL_FORCE usage

GUP now supports reliable R/O long-term pinning in COW mappings, such
that we break COW early. MAP_SHARED VMAs only use the shared zeropage so
far in one corner case (DAXFS file with holes), which can be ignored
because GUP does not support long-term pinning in fsdax (see
check_vma_flags()).

commit cd5297b0 ("drm/etnaviv: Use FOLL_FORCE for userptr")
documents that FOLL_FORCE | FOLL_WRITE was really only used for reliable
R/O pinning.

Consequently, FOLL_FORCE | FOLL_WRITE | FOLL_LONGTERM is no longer required
for reliable R/O long-term pinning: FOLL_LONGTERM is sufficient. So stop
using FOLL_FORCE, which is really only for ptrace access.

Link: https://lkml.kernel.org/r/20221116102659.70287-15-david@redhat.comSigned-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Lucas Stach <l.stach@pengutronix.de>
Cc: Russell King <linux+etnaviv@armlinux.org.uk>
Cc: Christian Gmeiner <christian.gmeiner@gmail.com>
Cc: David Airlie <airlied@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

drivers/gpu/drm/etnaviv/etnaviv_gem.c

@@ -638,6 +638,7 @@ static int etnaviv_gem_userptr_get_pages(struct etnaviv_gem_object *etnaviv_obj)
 	struct page **pvec = NULL;
 	struct etnaviv_gem_userptr *userptr = &etnaviv_obj->userptr;
 	int ret, pinned = 0, npages = etnaviv_obj->base.size >> PAGE_SHIFT;
+	unsigned int gup_flags = FOLL_LONGTERM;
 
 	might_lock_read(&current->mm->mmap_lock);
 
@@ -648,14 +649,15 @@ static int etnaviv_gem_userptr_get_pages(struct etnaviv_gem_object *etnaviv_obj)
 	if (!pvec)
 		return -ENOMEM;
 
+	if (!userptr->ro)
+		gup_flags |= FOLL_WRITE;
+
 	do {
 		unsigned num_pages = npages - pinned;
 		uint64_t ptr = userptr->ptr + pinned * PAGE_SIZE;
 		struct page **pages = pvec + pinned;
 
-		ret = pin_user_pages_fast(ptr, num_pages,
-					  FOLL_WRITE | FOLL_FORCE | FOLL_LONGTERM,
-					  pages);
+		ret = pin_user_pages_fast(ptr, num_pages, gup_flags, pages);
 		if (ret < 0) {
 			unpin_user_pages(pvec, pinned);
 			kvfree(pvec);