[PATCH resend v6 04/30] mm: add folio_zero_user stub for configs without THP/HUGETLBFS

[Michael S. Tsirkin]

folio_zero_user() is defined in mm/memory.c under
CONFIG_TRANSPARENT_HUGEPAGE || CONFIG_HUGETLBFS.  A subsequent patch
will call it from post_alloc_hook() for all user page zeroing, so
configs without THP or HUGETLBFS will need a stub.

Add a macro in the #else branch that falls back to
clear_user_highpages(), which handles cache aliasing correctly on
VIPT architectures and is always available via highmem.h.

Without THP/HUGETLBFS, only order-0 user pages are allocated, so
the locality optimization in the real folio_zero_user() (zero near
the faulting address last) is not needed.
This also matches what vma_alloc_zeroed_movable_folio currently does.

Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
Assisted-by: Claude:claude-opus-4-6
Assisted-by: cursor-agent:GPT-5.4-xhigh
---
 include/linux/mm.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index af23453e9dbd..3b1ca90fd435 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -5070,6 +5070,9 @@ long copy_folio_from_user(struct folio *dst_folio,
 			   const void __user *usr_src,
 			   bool allow_pagefault);
 
+#else /* !CONFIG_TRANSPARENT_HUGEPAGE && !CONFIG_HUGETLBFS */
+#define folio_zero_user(folio, addr_hint) \
+	clear_user_highpages(&(folio)->page, (addr_hint), folio_nr_pages(folio))
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE || CONFIG_HUGETLBFS */
 
 #if MAX_NUMNODES > 1
-- 
MST