+ mm-hugetlb_vmemmap-unify-writable-vmemmap-page-preparation.patch added to mm-unstable branch

+ mm-hugetlb_vmemmap-unify-writable-vmemmap-page-preparation.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm: hugetlb_vmemmap: unify writable vmemmap page preparation
has been added to the -mm mm-unstable branch.  Its filename is
     mm-hugetlb_vmemmap-unify-writable-vmemmap-page-preparation.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-hugetlb_vmemmap-unify-writable-vmemmap-page-preparation.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Muchun Song <muchun.song@linux.dev>
Subject: mm: hugetlb_vmemmap: unify writable vmemmap page preparation
Date: Sat, 07 Nov 2026 10:27:49 +0800

Installing a writable vmemmap page requires consuming a replacement page,
copying the current contents into it and making the copy visible before
publishing the new mapping.  HVO currently splits this sequence between
the page-table walker and its caller depending on the remap path.

Centralize the sequence in the walker so all writable replacements follow
the same copy-and-publish protocol.  This keeps page preparation with the
mapping update and removes path-specific handling from higher-level HVO
code.

No functional change intended.

Link: https://lore.kernel.org/20261107022756.77731-7-songmuchun@bytedance.com
Signed-off-by: Muchun Song <muchun.song@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Lance Yang <lance.yang@linux.dev>
Reviewed-by: Qi Zheng <qi.zheng@linux.dev>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Tested-by: Andrew Morton <akpm@linux-foundation.org>
Cc: James Houghton <jthoughton@google.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Yili Zhang <zhangyili01@baidu.com>
Cc: Kiryl Shutsemau <kas@kernel.org>
Cc: "Oscar Salvador (SUSE)" <osalvador@kernel.org>
Cc: Huacai Chen <chenhuacai@kernel.org>
---

 mm/hugetlb_vmemmap.c |   40 +++++++++++++++++-----------------------
 1 file changed, 17 insertions(+), 23 deletions(-)

--- a/mm/hugetlb_vmemmap.c~mm-hugetlb_vmemmap-unify-writable-vmemmap-page-preparation
+++ a/mm/hugetlb_vmemmap.c
@@ -199,6 +199,20 @@ static void free_vmemmap_page_list(struc
 		free_vmemmap_page(page);
 }
 
+static struct page *vmemmap_dup_page_from_list(const struct page *src,
+		struct list_head *vmemmap_pages)
+{
+	struct page *dst = list_first_entry(vmemmap_pages, struct page, lru);
+
+	list_del(&dst->lru);
+	copy_page(page_address(dst), page_address(src));
+
+	/* Ensure updates to @dst page are visible before set_pte_at(). */
+	smp_wmb();
+
+	return dst;
+}
+
 static void vmemmap_remap_pte(pte_t *pte, unsigned long addr,
 			      struct vmemmap_remap_walk *walk)
 {
@@ -211,16 +225,7 @@ static void vmemmap_remap_pte(pte_t *pte
 
 		VM_WARN_ON_ONCE(!PageHead((const struct page *)addr));
 
-		head = list_first_entry(walk->vmemmap_pages, struct page, lru);
-		list_del(&head->lru);
-
-		/*
-		 * Makes sure that preceding stores to the page contents from
-		 * vmemmap_remap_free() become visible before the set_pte_at()
-		 * write.
-		 */
-		smp_wmb();
-
+		head = vmemmap_dup_page_from_list(page, walk->vmemmap_pages);
 		entry = mk_pte(head, PAGE_KERNEL);
 	} else {
 		VM_WARN_ON_ONCE(!PageTail((const struct page *)addr));
@@ -253,15 +258,7 @@ static void vmemmap_restore_pte(pte_t *p
 
 	VM_WARN_ON_ONCE(PageHead((const struct page *)addr));
 
-	dst = list_first_entry(walk->vmemmap_pages, struct page, lru);
-	list_del(&dst->lru);
-	copy_page(page_to_virt(dst), page_to_virt(src));
-
-	/*
-	 * Makes sure that preceding stores to the page contents become visible
-	 * before the set_pte_at() write.
-	 */
-	smp_wmb();
+	dst = vmemmap_dup_page_from_list(src, walk->vmemmap_pages);
 	set_pte_at(&init_mm, addr, pte, mk_pte(dst, PAGE_KERNEL));
 }
 
@@ -501,7 +498,7 @@ static int __hugetlb_vmemmap_optimize_fo
 					    unsigned long flags)
 {
 	unsigned long vmemmap_start, vmemmap_end;
-	struct page *vmemmap_head, *vmemmap_tail;
+	struct page *vmemmap_tail;
 	gfp_t gfp_mask = GFP_KERNEL | __GFP_NOWARN;
 	int nid, ret = 0;
 
@@ -534,9 +531,6 @@ static int __hugetlb_vmemmap_optimize_fo
 	if (ret)
 		goto out;
 
-	vmemmap_head = list_first_entry(vmemmap_pages, struct page, lru);
-	copy_page(page_to_virt(vmemmap_head), folio);
-
 	vmemmap_start	= (unsigned long)&folio->page;
 	vmemmap_end	= vmemmap_start + hugetlb_vmemmap_size(h);
 
_

Patches currently in -mm which might be from muchun.song@linux.dev are

mm-fix-missing-page-table-destructor-in-pagetable_free.patch
riscv-mm-fix-hotplug-page-table-destructor-handling.patch
riscv-mm-fix-missing-destructor-for-hotplug-pud-tables.patch
arm64-mm-fix-destructor-for-unconstructed-hotplug-page-tables.patch
mm-sparse-vmemmap-map-shared-vmemmap-tail-pages-as-read-only.patch
powerpc-mm-map-shared-vmemmap-tail-pages-as-read-only.patch
mm-hugetlb_vmemmap-remove-vmemmap_wrprotect_hvo.patch
mm-hugetlb_vmemmap-remove-hugetlb_vmemmap_optimize_bootmem_folios.patch
mm-generalize-kernel-pte-table-allocation.patch
mm-generalize-pmd-page-table-allocation.patch
mm-generalize-pud-page-table-allocation.patch
mm-remove-pagetable_dtor_free.patch
mm-remove-redundant-pagetable_dtor-calls.patch
mm-hugetlb_vmemmap-remove-hugetlb-specific-vmemmap-optimization-macros.patch
mm-hugetlb_vmemmap-unify-vmemmap_splitremap_no_tlb_flush.patch
mm-hugetlb_vmemmap-simplify-vmemmap-head-page-handling.patch
mm-hugetlb_vmemmap-generalize-vmemmap-page-allocation.patch
mm-hugetlb_vmemmap-unify-writable-vmemmap-page-preparation.patch
mm-hugetlb_vmemmap-rename-vmemmap_remap_pte-to-vmemmap_optimize_pte.patch
mm-hugetlb_vmemmap-simplify-shared-tail-page-handling.patch
mm-hugetlb_vmemmap-move-alloc_vmemmap_page_list-next-to-its-free-helper.patch
mm-hugetlb_vmemmap-make-vmemmap-optimization-folio-oriented.patch
mm-hugetlb_vmemmap-make-vmemmap-restoration-folio-oriented.patch
mm-hugetlb_vmemmap-unify-vmemmap-range-restoration.patch
mm-hugetlb_vmemmap-make-vmemmap-pte-conversion-folio-oriented.patch
mm-hugetlb-fix-validation-of-unsupported-hugetlb-orders.patch