[PATCH v9 10/37] 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 stub that uses clear_user_highpages() with aligned
addr_hint.

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 | 2 ++
 mm/memory.c        | 9 +++++++++
 2 files changed, 11 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index af23453e9dbd..d1e768dcda13 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -5070,6 +5070,8 @@ long copy_folio_from_user(struct folio *dst_folio,
 			   const void __user *usr_src,
 			   bool allow_pagefault);
 
+#else /* !CONFIG_TRANSPARENT_HUGEPAGE && !CONFIG_HUGETLBFS */
+void folio_zero_user(struct folio *folio, unsigned long addr_hint);
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE || CONFIG_HUGETLBFS */
 
 #if MAX_NUMNODES > 1
diff --git a/mm/memory.c b/mm/memory.c
index ea6568571131..02d3e53fc91b 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -7546,6 +7546,15 @@ long copy_folio_from_user(struct folio *dst_folio,
 }
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE || CONFIG_HUGETLBFS */
 
+#if !defined(CONFIG_TRANSPARENT_HUGEPAGE) && !defined(CONFIG_HUGETLBFS)
+void folio_zero_user(struct folio *folio, unsigned long addr_hint)
+{
+	unsigned long base = ALIGN_DOWN(addr_hint, folio_size(folio));
+
+	clear_user_highpages(&folio->page, base, folio_nr_pages(folio));
+}
+#endif
+
 #if defined(CONFIG_SPLIT_PTE_PTLOCKS) && ALLOC_SPLIT_PTLOCKS
 
 static struct kmem_cache *page_ptl_cachep;
-- 
MST