[PATCH RFC v1 02/12] mm/usercopy.c: Prepare check_page_span() for PG_reserved changes

[David Hildenbrand <david@redhat.com>]

Right now, ZONE_DEVICE memory is always set PG_reserved. We want to
change that.

Let's make sure that the logic in the function won't change. Once we no
longer set these pages to reserved, we can rework this function to
perform separate checks for ZONE_DEVICE (split from PG_reserved checks).

Cc: Kees Cook <keescook@chromium.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Kate Stewart <kstewart@linuxfoundation.org>
Cc: Allison Randal <allison@lohutok.net>
Cc: "Isaac J. Manjarres" <isaacm@codeaurora.org>
Cc: Qian Cai <cai@lca.pw>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 mm/usercopy.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/usercopy.c b/mm/usercopy.c
index 660717a1ea5c..a3ac4be35cde 100644
--- a/mm/usercopy.c
+++ b/mm/usercopy.c
@@ -203,14 +203,15 @@ static inline void check_page_span(const void *ptr, unsigned long n,
 	 * device memory), or CMA. Otherwise, reject since the object spans
 	 * several independently allocated pages.
 	 */
-	is_reserved = PageReserved(page);
+	is_reserved = PageReserved(page) || is_zone_device_page(page);
 	is_cma = is_migrate_cma_page(page);
 	if (!is_reserved && !is_cma)
 		usercopy_abort("spans multiple pages", NULL, to_user, 0, n);
 
 	for (ptr += PAGE_SIZE; ptr <= end; ptr += PAGE_SIZE) {
 		page = virt_to_head_page(ptr);
-		if (is_reserved && !PageReserved(page))
+		if (is_reserved && !(PageReserved(page) ||
+				     is_zone_device_page(page)))
 			usercopy_abort("spans Reserved and non-Reserved pages",
 				       NULL, to_user, 0, n);
 		if (is_cma && !is_migrate_cma_page(page))
-- 
2.21.0