[PATCH 17/27] mm/gup: fail get_user_pages for LONGTERM dev coherent type

[Christoph Hellwig]

From: Alex Sierra <alex.sierra@xxxxxxx>

Avoid long term pinning for Coherent device type pages. This could
interfere with their own device memory manager. For now, we are just
returning error for PIN_LONGTERM Coherent device type pages. Eventually,
these type of pages will get migrated to system memory, once the device
migration pages support is added.

Signed-off-by: Alex Sierra <alex.sierra@xxxxxxx>
Acked-by: Felix Kuehling <Felix.Kuehling@xxxxxxx>
Reviewed-by: Alistair Poppple <apopple@xxxxxxxxxx>
[hch: rebased on previous cleanups, split the two checks]
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
---
 mm/gup.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/mm/gup.c b/mm/gup.c
index 37d6c24ca71225..39b23ad39a7bde 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1881,6 +1881,19 @@ static long check_and_migrate_movable_pages(unsigned long nr_pages,
 			continue;
 		prev_head = head;
 
+		/*
+		 * Device private pages will get faulted in during gup so it
+		 * shouldn't be possible to see one here.
+		 */
+		if (WARN_ON_ONCE(is_device_private_page(head))) {
+			ret = -EFAULT;
+			goto unpin_pages;
+		}
+		if (is_device_coherent_page(head)) {
+			ret = -EFAULT;
+			goto unpin_pages;
+		}
+
 		if (is_pinnable_page(head))
 			continue;
 
@@ -1925,7 +1938,7 @@ static long check_and_migrate_movable_pages(unsigned long nr_pages,
 			put_page(pages[i]);
 	}
 
-	if (!list_empty(&movable_page_list)) {
+	if (!ret && !list_empty(&movable_page_list)) {
 		struct migration_target_control mtc = {
 			.nid = NUMA_NO_NODE,
 			.gfp_mask = GFP_USER | __GFP_NOWARN,
-- 
2.30.2