[PATCH] mm/huge_memory: restrict __GFP_ZEROTAGS to HW tagging architectures

[Jan Polensky]

The previous change added __GFP_ZEROTAGS when allocating the huge zero
folio to ensure tag initialization for arm64 with MTE enabled. However,
on s390 this flag is unnecessary and triggers a regression
(observed as a crash during repeated 'dnf makecache').

Restrict the use of __GFP_ZEROTAGS to architectures that support
hardware memory tagging (currently arm64 with MTE or KASAN HW tags).
This avoids unintended side effects on other platforms.

Fixes: 1579227fe0f0 ("mm/huge_memory: initialise the tags of the huge zero folio")
Link: https://lore.kernel.org/r/20251031170133.280742-1-catalin.marinas@arm.com
Signed-off-by: Jan Polensky <japo at linux.ibm.com>
---
 mm/huge_memory.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index aae283b00857..0c1794656d7a 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -209,14 +209,15 @@ unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma,

 static bool get_huge_zero_folio(void)
 {
+	gfp_t gfp = (GFP_TRANSHUGE | __GFP_ZERO) & ~__GFP_MOVABLE;
 	struct folio *zero_folio;
 retry:
 	if (likely(atomic_inc_not_zero(&huge_zero_refcount)))
 		return true;
-
-	zero_folio = folio_alloc((GFP_TRANSHUGE | __GFP_ZERO | __GFP_ZEROTAGS) &
-				 ~__GFP_MOVABLE,
-			HPAGE_PMD_ORDER);
+#if IS_ENABLED(CONFIG_KASAN_HW_TAGS) || IS_ENABLED(CONFIG_ARM64_MTE)
+	gfp |= __GFP_ZEROTAGS;
+#endif
+	zero_folio = folio_alloc(gfp, HPAGE_PMD_ORDER);
 	if (!zero_folio) {
 		count_vm_event(THP_ZERO_PAGE_ALLOC_FAILED);
 		return false;
--
2.48.1