+ mm-hugetlb_vmemmap-unify-vmemmap_splitremap_no_tlb_flush.patch added to mm-unstable branch

+ mm-hugetlb_vmemmap-unify-vmemmap_splitremap_no_tlb_flush.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm: hugetlb_vmemmap: unify VMEMMAP_{SPLIT,REMAP}_NO_TLB_FLUSH
has been added to the -mm mm-unstable branch.  Its filename is
     mm-hugetlb_vmemmap-unify-vmemmap_splitremap_no_tlb_flush.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-vmemmap_splitremap_no_tlb_flush.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 VMEMMAP_{SPLIT,REMAP}_NO_TLB_FLUSH
Date: Sat, 07 Nov 2026 10:27:46 +0800

VMEMMAP_SPLIT_NO_TLB_FLUSH and VMEMMAP_REMAP_NO_TLB_FLUSH do not
describe fully independent choices. A split-only walk can defer the
PMD-split flush to a later global flush, and a remap-only walk can
defer the final remap flush. However, when a PMD split is followed
by PTE remapping, the split flush must happen before the PTEs are
changed, because stale large-page translations must not overlap with
new small-page translations that map different physical pages.

Replace the two flags with a single VMEMMAP_DEFER_TLB_FLUSH flag. The
new name reflects that only safely batchable flushes are deferred. Keep
split-only walks able to defer the flush, but force the split flush
whenever a remap_pte callback is present. Callers that batch HVO work
can still defer the final remap flush and issue their own global flush.

Current callers keep the same flushing behavior.

Link: https://lore.kernel.org/20261107022756.77731-4-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: Oscar Salvador <osalvador@suse.de>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
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 |   23 +++++++++++++----------
 1 file changed, 13 insertions(+), 10 deletions(-)

--- a/mm/hugetlb_vmemmap.c~mm-hugetlb_vmemmap-unify-vmemmap_splitremap_no_tlb_flush
+++ a/mm/hugetlb_vmemmap.c
@@ -42,10 +42,8 @@ struct vmemmap_remap_walk {
 	struct list_head	*vmemmap_pages;
 
 
-/* Skip the TLB flush when we split the PMD */
-#define VMEMMAP_SPLIT_NO_TLB_FLUSH	BIT(0)
-/* Skip the TLB flush when we remap the PTE */
-#define VMEMMAP_REMAP_NO_TLB_FLUSH	BIT(1)
+/* Defer safely batchable TLB flushes to the caller. */
+#define VMEMMAP_DEFER_TLB_FLUSH	BIT(0)
 	unsigned long		flags;
 };
 
@@ -85,7 +83,12 @@ static int vmemmap_split_pmd(pmd_t *pmd,
 		/* Make pte visible before pmd. See comment in pmd_install(). */
 		smp_wmb();
 		pmd_populate_kernel(&init_mm, pmd, pgtable);
-		if (!(walk->flags & VMEMMAP_SPLIT_NO_TLB_FLUSH))
+		/*
+		 * Modern MMUs allow overlapping TLB entries with different mapping
+		 * granularities only if they map the same physical address. So
+		 * remapping must not proceed without first flushing the TLB.
+		 */
+		if (walk->remap_pte || !(walk->flags & VMEMMAP_DEFER_TLB_FLUSH))
 			flush_tlb_kernel_range(start, start + PMD_SIZE);
 	} else {
 		pte_free_kernel(&init_mm, pgtable);
@@ -166,7 +169,7 @@ static int vmemmap_remap_range(unsigned
 	if (ret)
 		return ret;
 
-	if (walk->remap_pte && !(walk->flags & VMEMMAP_REMAP_NO_TLB_FLUSH))
+	if (walk->remap_pte && !(walk->flags & VMEMMAP_DEFER_TLB_FLUSH))
 		flush_tlb_kernel_range(start, end);
 
 	return 0;
@@ -274,7 +277,7 @@ static int vmemmap_remap_split(unsigned
 {
 	struct vmemmap_remap_walk walk = {
 		.remap_pte	= NULL,
-		.flags		= VMEMMAP_SPLIT_NO_TLB_FLUSH,
+		.flags		= VMEMMAP_DEFER_TLB_FLUSH,
 	};
 
 	return vmemmap_remap_range(start, end, &walk);
@@ -458,7 +461,7 @@ long hugetlb_vmemmap_restore_folios(cons
 	struct folio *folio, *t_folio;
 	long restored = 0;
 	long ret = 0;
-	unsigned long flags = VMEMMAP_REMAP_NO_TLB_FLUSH;
+	unsigned long flags = VMEMMAP_DEFER_TLB_FLUSH;
 
 	list_for_each_entry_safe(folio, t_folio, folio_list, lru) {
 		if (folio_test_hugetlb_vmemmap_optimized(folio)) {
@@ -517,7 +520,7 @@ static int __hugetlb_vmemmap_optimize_fo
 
 	/*
 	 * Very Subtle
-	 * If VMEMMAP_REMAP_NO_TLB_FLUSH is set, TLB flushing is not performed
+	 * If VMEMMAP_DEFER_TLB_FLUSH is set, TLB flushing is not performed
 	 * immediately after remapping.  As a result, subsequent accesses
 	 * and modifications to struct pages associated with the hugetlb
 	 * page could be to the OLD struct pages.  Set the vmemmap optimized
@@ -596,7 +599,7 @@ void hugetlb_vmemmap_optimize_folios(str
 	struct folio *folio;
 	unsigned long nr_to_optimize = 0;
 	LIST_HEAD(vmemmap_pages);
-	unsigned long flags = VMEMMAP_REMAP_NO_TLB_FLUSH;
+	unsigned long flags = VMEMMAP_DEFER_TLB_FLUSH;
 
 	if (list_empty(folio_list))
 		return;
_

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