arm64: mte: Do not warn if the page is already tagged in copy_highpage()

[ Upstream commit b98c94e ]

The arm64 copy_highpage() assumes that the destination page is newly
allocated and not MTE-tagged (PG_mte_tagged unset) and warns
accordingly. However, following commit 0609139 ("mm: migrate:
support poisoned recover from migrate folio"), folio_mc_copy() is called
before __folio_migrate_mapping(). If the latter fails (-EAGAIN), the
copy will be done again to the same destination page. Since
copy_highpage() already set the PG_mte_tagged flag, this second copy
will warn.

Replace the WARN_ON_ONCE(page already tagged) in the arm64
copy_highpage() with a comment.

Reported-by: [email protected]
Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: David Hildenbrand <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Kefeng Wang <[email protected]>
Cc: [email protected] # 6.12.x
Reviewed-by: Yang Shi <[email protected]>
Signed-off-by: Catalin Marinas <[email protected]>
[ omitted hugetlb MTE changes ]
Signed-off-by: Sasha Levin <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: ctmarinas

arch/arm64/mm/copypage.c

@@ -25,8 +25,13 @@ void copy_highpage(struct page *to, struct page *from)
 		page_kasan_tag_reset(to);
 
 	if (system_supports_mte() && page_mte_tagged(from)) {
-		/* It's a new page, shouldn't have been tagged yet */
-		WARN_ON_ONCE(!try_page_mte_tagging(to));
+		/*
+		 * Most of the time it's a new page that shouldn't have been
+		 * tagged yet. However, folio migration can end up reusing the
+		 * same page without untagging it. Ignore the warning if the
+		 * page is already tagged.
+		 */
+		try_page_mte_tagging(to);
 		mte_copy_page_tags(kto, kfrom);
 		set_page_mte_tagged(to);
 	}