mm: Preserve the PG_arch_2 flag in __split_huge_page_tail()

When a huge page is split into normal pages, part of the head page flags
are transferred to the tail pages. However, the PG_arch_* flags are not
part of the preserved set.

PG_arch_2 is used by the arm64 MTE support to mark pages that have valid
tags. The absence of such flag would cause the arm64 set_pte_at() to
clear the tags in order to avoid stale tags exposed to user or the
swapping out hooks to ignore the tags. Not preserving PG_arch_2 on huge
page splitting leads to tag corruption in the tail pages.

Preserve the newly added PG_arch_2 flag in __split_huge_page_tail().

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 2ccff84..1a5773c 100644 (file)
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2337,6 +2337,9 @@ static void __split_huge_page_tail(struct page *head, int tail,
                         (1L << PG_workingset) |
                         (1L << PG_locked) |
                         (1L << PG_unevictable) |
+#ifdef CONFIG_64BIT
+                        (1L << PG_arch_2) |
+#endif
                         (1L << PG_dirty)));
 
        /* ->mapping in first tail page is compound_mapcount */