[PATCH STABLE v4.19.y] mm/migrate: set swap entry values of THP tail pages properly.

[Zi Yan <zi.yan@sent.com>]

From: Zi Yan <ziy@nvidia.com>

The tail pages in a THP can have swap entry information stored in their
private field. When migrating to a new page, all tail pages of the new
page need to update ->private to avoid future data corruption.

Corresponding swapcache entries need to be updated as well.
e71769ae5260 ("mm: enable thp migration for shmem thp") fixed it already.

Closes: https://lore.kernel.org/linux-mm/1707814102-22682-1-git-send-email-quic_charante@quicinc.com/
Fixes: 616b8371539a ("mm: thp: enable thp migration in generic path")
Signed-off-by: Zi Yan <ziy@nvidia.com>
---
 mm/migrate.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index 171573613c39..893ea04498f7 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -514,8 +514,12 @@ int migrate_page_move_mapping(struct address_space *mapping,
 	if (PageSwapBacked(page)) {
 		__SetPageSwapBacked(newpage);
 		if (PageSwapCache(page)) {
+			int i;
+
 			SetPageSwapCache(newpage);
-			set_page_private(newpage, page_private(page));
+			for (i = 0; i < (1 << compound_order(page)); i++)
+				set_page_private(newpage + i,
+						 page_private(page + i));
 		}
 	} else {
 		VM_BUG_ON_PAGE(PageSwapCache(page), page);
-- 
2.43.0