net/rds: Detect need of On-Demand-Paging memory registration

Add code to check if memory intended for RDMA is FS-DAX-memory. RDS
will fail with error code EOPNOTSUPP if FS-DAX-memory is detected.
Signed-off-by: Hans Westgaard Ry <hans.westgaard.ry@oracle.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>

net/rds/rdma.c

@@ -156,11 +156,13 @@ void rds_rdma_drop_keys(struct rds_sock *rs)
 static int rds_pin_pages(unsigned long user_addr, unsigned int nr_pages,
 			struct page **pages, int write)
 {
+	unsigned int gup_flags = FOLL_LONGTERM;
 	int ret;
 
-	ret = get_user_pages_fast(user_addr, nr_pages, write ? FOLL_WRITE : 0,
-				  pages);
+	if (write)
+		gup_flags |= FOLL_WRITE;
 
+	ret = get_user_pages_fast(user_addr, nr_pages, gup_flags, pages);
 	if (ret >= 0 && ret < nr_pages) {
 		while (ret--)
 			put_page(pages[ret]);