RDMA/siw: 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()).

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/20221116102659.70287-13-david@redhat.comSigned-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Cc: Bernard Metzler <bmt@zurich.ibm.com>
Cc: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

drivers/infiniband/sw/siw/siw_mem.c

@@ -368,7 +368,7 @@ struct siw_umem *siw_umem_get(u64 start, u64 len, bool writable)
 	struct mm_struct *mm_s;
 	u64 first_page_va;
 	unsigned long mlock_limit;
-	unsigned int foll_flags = FOLL_WRITE;
+	unsigned int foll_flags = FOLL_LONGTERM;
 	int num_pages, num_chunks, i, rv = 0;
 
 	if (!can_do_mlock())
@@ -391,8 +391,8 @@ struct siw_umem *siw_umem_get(u64 start, u64 len, bool writable)
 
 	mmgrab(mm_s);
 
-	if (!writable)
-		foll_flags |= FOLL_FORCE;
+	if (writable)
+		foll_flags |= FOLL_WRITE;
 
 	mmap_read_lock(mm_s);
 
@@ -423,8 +423,7 @@ struct siw_umem *siw_umem_get(u64 start, u64 len, bool writable)
 		while (nents) {
 			struct page **plist = &umem->page_chunk[i].plist[got];
 
-			rv = pin_user_pages(first_page_va, nents,
-					    foll_flags | FOLL_LONGTERM,
+			rv = pin_user_pages(first_page_va, nents, foll_flags,
 					    plist, NULL);
 			if (rv < 0)
 				goto out_sem_up;