+ mm-mlock-eliminate-weird-vma_io_bit-abuse-and-simplify.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm/mlock: eliminate weird VMA_IO_BIT abuse and simplify
has been added to the -mm mm-unstable branch.  Its filename is
     mm-mlock-eliminate-weird-vma_io_bit-abuse-and-simplify.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-mlock-eliminate-weird-vma_io_bit-abuse-and-simplify.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: "Lorenzo Stoakes (ARM)" <ljs@kernel.org>
Subject: mm/mlock: eliminate weird VMA_IO_BIT abuse and simplify
Date: Fri, 09 Oct 2026 19:04:17 +0100

When performing mlock() or munlock() otherwise normal VMAs have VMA_IO_BIT
solely to fix a race with migration which might otherwise double-count
mlock VMAs.

This is unnecessary - at the point of applying folio mlock state, whether
setting or clearing PG_mlocked, we know whether or not we are locking.

Solve this in two ways - thread a boolean through the page table walk
indicating whether a lock or unlock is being performed, and run a locking
walk with VMA_LOCKONFAULT_BIT set and VMA_LOCKED_BIT cleared.

This state never occurs otherwise, as VMA_LOCKONFAULT_BIT always implies
VMA_LOCKED_BIT. These are also always cleared together.

Then, update folio_add_lru_vma() and mlock_folio() to check only for
VMA_LOCKED_BIT, and update try_to_unmap_one() to check for VMA_LOCKED_MASK
instead.

Also remove the useless invocation of allow_mlock_munlock() which simply
returns true if unlocking and instead rename it to allow_mlock() and only
call it when locking.

With the other mlock abuse of VMA_IO_BIT addressed, update
mlock_vma_folio() and folio_add_lru_vma() to simply test for
VMA_LOCKED_BIT.

The munlock_vma_folio() function tests VMA_LOCKED_MASK instead, as an
unmap racing with the locking walk must still munlock folios the walk has
already counted.

Additionally, in order to ensure a racing unmap/migration releases the
reference munlock_folio() took (whose put was batched), check
VMA_LOCKED_MASK before calling mlock_drain_local() in try_to_unmap_one()
and try_to_migrate_one().

While here, also replace some deprecated VMA flag predicates.

Link: https://lore.kernel.org/20261009-b4-mmap-prepare-vma-flag-sanify-v5-23-923b70125b1e@kernel.org
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: David Hildenbrand <david@kernel.org>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Dennis Dalessandro <dennis.dalessandro@cornelisnetworks.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Leon Romanovsky <leon@kernel.org>
Cc: Paul Moore <paul@paul-moore.com>
Cc: Stephen Smalley <stephen.smalley.work@gmail.com>
Cc: Jaroslav Kysela <perex@perex.cz>
Cc: Takashi Iwai <tiwai@suse.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Eduard Zingerman <eddyz87@gmail.com>
Cc: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Nico Pache <nico.pache@linux.dev>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Usama Arif <usama.arif@linux.dev>
Cc: Kiryl Shutsemau <kas@kernel.org>
Cc: Doug Gilbert <dgilbert@interlog.com>
Cc: James Bottomley <james.bottomley@hansenpartnership.com>
Cc: Martin K. Petersen <mkp@kernel.org>
Cc: Simona Vetter <simona@ffwll.ch>
Cc: Helge Deller <deller@gmx.de>
Cc: Sebastian Reichel <sre@kernel.org>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Harry Yoo <harry@kernel.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: David Airlie <airlied@gmail.com>
Cc: Will Deacon <will@kernel.org>
Cc: Aneesh Kumar K.V <aneesh.kumar@kernel.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Oliver Upton <oupton@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Anup Patel <anup@brainfault.org>
Cc: Paul Walmsley <pjw@kernel.org>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Janosch Frank <frankja@linux.ibm.com>
Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Andreas Larsson <andreas@gaisler.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Rakie Kim <rakie.kim@sk.com>
Cc: Byungchul Park <byungchul@sk.com>
Cc: Gregory Price <gourry@gourry.net>
Cc: Ying Huang <ying.huang@linux.alibaba.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Chris Li <chrisl@kernel.org>
Cc: Kairui Song <kasong@tencent.com>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Baoquan He <baoquan.he@linux.dev>
Cc: Youngjun Park <youngjun.park@lge.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Qi Zheng <qi.zheng@linux.dev>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Yuanchu Xie <yuanchu@google.com>
Cc: Wei Xu <weixugc@google.com>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Miklos Szeredi <miklos@szeredi.hu>
Cc: Xu Xin <xu.xin@linux.dev>
Cc: Ihor Solodrai <ihor.solodrai@linux.dev>
Cc: Bert Karwatzki <spasswolf@web.de>
---

 mm/folio.c    |    2 -
 mm/internal.h |   10 ++++++---
 mm/mlock.c    |   51 +++++++++++++++++-------------------------------
 mm/rmap.c     |    8 ++++---
 4 files changed, 32 insertions(+), 39 deletions(-)

--- a/mm/folio.c~mm-mlock-eliminate-weird-vma_io_bit-abuse-and-simplify
+++ a/mm/folio.c
@@ -505,7 +505,7 @@ void folio_add_lru_vma(struct folio *fol
 {
 	VM_BUG_ON_FOLIO(folio_test_lru(folio), folio);
 
-	if (unlikely((vma->vm_flags & (VM_LOCKED | VM_SPECIAL)) == VM_LOCKED))
+	if (vma_test(vma, VMA_LOCKED_BIT))
 		mlock_new_folio(folio);
 	else
 		folio_add_lru(folio);
--- a/mm/internal.h~mm-mlock-eliminate-weird-vma_io_bit-abuse-and-simplify
+++ a/mm/internal.h
@@ -970,8 +970,7 @@ void mlock_folio(struct folio *folio);
 static inline void mlock_vma_folio(struct folio *folio,
 				struct vm_area_struct *vma)
 {
-	/* The VM_IO check prevents migration from double-counting during mlock. */
-	if (unlikely((vma->vm_flags & (VM_LOCKED|VM_SPECIAL)) == VM_LOCKED))
+	if (vma_test(vma, VMA_LOCKED_BIT))
 		mlock_folio(folio);
 }
 
@@ -988,7 +987,12 @@ static inline void munlock_vma_folio(str
 	 * always munlock the folio and page reclaim will correct it
 	 * if it's wrong.
 	 */
-	if (unlikely(vma->vm_flags & VM_LOCKED))
+	/*
+	 * VMA_LOCKONFAULT_BIT alone marks an mlock walk in progress, see
+	 * mlock_vma_pages_range(). An unmap racing with the walk must still
+	 * munlock folios the walk has already counted.
+	 */
+	if (unlikely(vma_test_any_mask(vma, VMA_LOCKED_MASK)))
 		munlock_folio(folio);
 }
 
--- a/mm/mlock.c~mm-mlock-eliminate-weird-vma_io_bit-abuse-and-simplify
+++ a/mm/mlock.c
@@ -316,22 +316,10 @@ static inline unsigned int folio_mlock_s
 	return folio_pte_batch(folio, pte, ptent, count);
 }
 
-static inline bool allow_mlock_munlock(struct folio *folio,
+static inline bool allow_mlock(struct folio *folio,
 		struct vm_area_struct *vma, unsigned long start,
 		unsigned long end, unsigned int step)
 {
-	/*
-	 * For unlock, allow munlock large folio which is partially
-	 * mapped to VMA. As it's possible that large folio is
-	 * mlocked and VMA is split later.
-	 *
-	 * During memory pressure, such kind of large folio can
-	 * be split. And the pages are not in VM_LOCKed VMA
-	 * can be reclaimed.
-	 */
-	if (!vma_test(vma, VMA_LOCKED_BIT))
-		return true;
-
 	/* folio_within_range() cannot take KSM, but any small folio is OK */
 	if (!folio_test_large(folio))
 		return true;
@@ -352,6 +340,7 @@ static int mlock_pte_range(pmd_t *pmd, u
 
 {
 	struct vm_area_struct *vma = walk->vma;
+	const bool lock = walk->private;
 	spinlock_t *ptl;
 	pte_t *start_pte, *pte;
 	pte_t ptent;
@@ -368,7 +357,7 @@ static int mlock_pte_range(pmd_t *pmd, u
 		folio = pmd_folio(*pmd);
 		if (folio_is_zone_device(folio))
 			goto out;
-		if (vma_test(vma, VMA_LOCKED_BIT))
+		if (lock)
 			mlock_folio(folio);
 		else
 			munlock_folio(folio);
@@ -390,10 +379,10 @@ static int mlock_pte_range(pmd_t *pmd, u
 			continue;
 
 		step = folio_mlock_step(folio, pte, addr, end);
-		if (!allow_mlock_munlock(folio, vma, start, end, step))
+		if (lock && !allow_mlock(folio, vma, start, end, step))
 			goto next_entry;
 
-		if (vma_test(vma, VMA_LOCKED_BIT))
+		if (lock)
 			mlock_folio(folio);
 		else
 			munlock_folio(folio);
@@ -428,31 +417,29 @@ static void mlock_vma_pages_range(struct
 		.pmd_entry = mlock_pte_range,
 		.walk_lock = PGWALK_WRLOCK_VERIFY,
 	};
+	const bool lock = vma_flags_test(new_vma_flags, VMA_LOCKED_BIT);
+	vma_flags_t walk_flags = *new_vma_flags;
 
 	/*
-	 * There is a slight chance that concurrent page migration,
-	 * or page reclaim finding a page of this now-VMA_LOCKED_BIT vma,
-	 * will call mlock_vma_folio() and raise page's mlock_count:
-	 * double counting, leaving the page unevictable indefinitely.
-	 * Communicate this danger to mlock_vma_folio() with VMA_IO_BIT,
-	 * which is a VMA_SPECIAL_FLAGS flag not allowed on VMA_LOCKED_BIT vmas.
-	 * mmap_lock is held in write mode here, so this weird
-	 * combination should not be visible to other mmap_lock users;
-	 * but WRITE_ONCE so rmap walkers must see VMA_IO_BIT if VMA_LOCKED_BIT.
+	 * LOCKONFAULT without LOCKED never otherwise occurs: it marks a walk in
+	 * progress so that rmap-side callers, which test VMA_LOCKED_BIT, do not
+	 * count folios, while try_to_unmap_one(), which tests VMA_LOCKED_MASK,
+	 * still refuses to unmap them.
 	 */
-	if (vma_flags_test(new_vma_flags, VMA_LOCKED_BIT))
-		vma_flags_set(new_vma_flags, VMA_IO_BIT);
+	if (lock) {
+		vma_flags_clear(&walk_flags, VMA_LOCKED_BIT);
+		vma_flags_set(&walk_flags, VMA_LOCKONFAULT_BIT);
+	}
+
 	vma_start_write(vma);
-	vma_flags_reset_once(vma, new_vma_flags);
+	vma_flags_reset_once(vma, &walk_flags);
 
 	lru_add_drain();
-	walk_page_range_vma(vma, start, end, &mlock_walk_ops, NULL);
+	walk_page_range_vma(vma, start, end, &mlock_walk_ops, (void *)lock);
 	lru_add_drain();
 
-	if (vma_flags_test(new_vma_flags, VMA_IO_BIT)) {
-		vma_flags_clear(new_vma_flags, VMA_IO_BIT);
+	if (lock)
 		vma_flags_reset_once(vma, new_vma_flags);
-	}
 }
 
 /*
--- a/mm/rmap.c~mm-mlock-eliminate-weird-vma_io_bit-abuse-and-simplify
+++ a/mm/rmap.c
@@ -2239,9 +2239,11 @@ static bool try_to_unmap_one(struct foli
 
 		/*
 		 * If the folio is in an mlock()d vma, we must not swap it out.
+		 * VMA_LOCKONFAULT_BIT alone marks an mlock walk in progress, see
+		 * mlock_vma_pages_range().
 		 */
 		if (!(flags & TTU_IGNORE_MLOCK) &&
-		    (vma->vm_flags & VM_LOCKED)) {
+		    vma_test_any_mask(vma, VMA_LOCKED_MASK)) {
 			ptes++;
 
 			/*
@@ -2395,7 +2397,7 @@ static bool try_to_unmap_one(struct foli
 		}
 finish_unmap:
 		folio_remove_rmap_ptes(folio, page, nr_pages, vma);
-		if (vma->vm_flags & VM_LOCKED)
+		if (vma_test_any_mask(vma, VMA_LOCKED_MASK))
 			mlock_drain_local();
 		folio_put_refs(folio, nr_pages);
 
@@ -2770,7 +2772,7 @@ static bool try_to_migrate_one(struct fo
 			hugetlb_remove_rmap(folio);
 		else
 			folio_remove_rmap_pte(folio, subpage, vma);
-		if (vma->vm_flags & VM_LOCKED)
+		if (vma_test_any_mask(vma, VMA_LOCKED_MASK))
 			mlock_drain_local();
 		folio_put(folio);
 	}
_

Patches currently in -mm which might be from ljs@kernel.org are

mm-vma-fix-mmap_prepare-file-handling-remove-file_doesnt_need_get.patch
mm-vma-introduce-and-use-vma_can_merge.patch
mm-consistently-validate-vma-state-after-mmap-hooks.patch
mm-vma-ensure-mmap_prepare-doesnt-set-actions-on-a-mergeable-vma.patch
mm-make-map_kernel_pages_-internal-and-unexported.patch
mm-vma-tidy-up-map-kernel-pages-enum-values.patch
mm-add-mmap-action-for-discontiguous-kernel-page-mapping.patch
docs-filesystems-update-mmap_prepare-docs-for-discontig-kernel-pgs.patch
drivers-usb-mon-update-to-use-mmap_prepare-map-kernel-pages.patch
infiniband-update-hfi1-to-use-remap_vmalloc_range.patch
selinux-reject-writable-opens-of-policy-file-drop-mmap-shared-write-check.patch
alsa-pcm-use-vm_insert_page-to-map-pcm-status-page.patch
bpf-arena-mark-arena_map_mmap-mappings-vm_mixedmap.patch
mm-vma-add-vma_is_mm_managed-predicates.patch
mm-vma-only-allow-mmap-to-clear-vma_maywrite_bit-if-not-mm-managed.patch
mm-vma-add-and-use-vma__is_fixed_mapping.patch
scsi-sg-convert-mmap-hook-to-mmap_prepare-and-rework.patch
fbdev-defio-assert-fbinfo_virtfb-drop-vm_io-add-vm_mixedmap.patch
hsi-cmt_speech-convert-mmap-hook-to-mmap_prepare-refactor.patch
mm-gup-error-out-early-on-vma_mayread_bit-vmas.patch
uprobes-remove-vm_io-set-vm_mixedmap-for-mapped-kernel-pages.patch
mm-mlock-clear-vma_locked_mask-over-mmap-callback.patch
mm-mlock-eliminate-weird-vma_io_bit-abuse-and-simplify.patch
mm-vma-enforce-that-mm-managed-mappings-may-not-set-vma_io_bit.patch
mm-remove-vma_io_bit-check-in-vma_is_mm_managed.patch
mm-remove-hugetlb_inlineh.patch
mm-rename-is_vm_hugetlb_page-to-vma_is_hugetlb.patch
mm-drop-some-redundant-checks-around-hugetlb-vmas.patch
mm-madvise-update-is_valid_guard_vma-to-use-vma_can_merge.patch
mm-vma-introduce-vma_is_mm_backed.patch
mm-uffd-use-predicates-for-userfaultfd-checks.patch
mm-madvise-use-predicates-for-madvise-madv_dofork.patch
mm-eliminate-vma_special_flags-usage-when-hugetlb-explicitly-tested.patch
mm-eliminate-vma_special_flags-check-in-lru_gen_look_around.patch
mm-avoid-use-of-vma_special_flags-in-migrate_vma_setup.patch
mm-eliminate-vm_special-vma_special_flags.patch
fuse-dax-do-not-set-vm_mixedmap.patch
mm-huge_memory-remove-vma_is_special_huge.patch
mm-vma-const-ify-vma_assert_stabilised-and-associated-functions.patch
mm-implement-and-use-vma_has_anon_rmap-silence-kcsan.patch
mm-update-comments-to-refer-to-anon-rmap-rather-than-anon_vma.patch
mm-vma-dont-remove-vma-from-rmap-if-pgoff-unchanged.patch