From: Andrew Morton <akpm@linux-foundation.org>
To: mm-commits@vger.kernel.org,muchun.song@linux.dev,akpm@linux-foundation.org
Subject: + mm-hugetlb_vmemmap-unify-vmemmap_splitremap_no_tlb_flush.patch added to mm-unstable branch
Date: Fri, 06 Nov 2026 19:53:37 -0800 [thread overview]
Message-ID: <20261107035337.915FA1F0089F@smtp.kernel.org> (raw)
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
reply other threads:[~2026-11-07 3:53 UTC|newest]
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