[PATCH v4 1/6] mm: enable page walking API to lock vmas during the walk

From: Suren Baghdasaryan
Date: Fri Aug 04 2023 - 11:28:16 EST

walk_page_range() and friends often operate under write-locked mmap_lock.
With introduction of vma locks, the vmas have to be locked as well
during such walks to prevent concurrent page faults in these areas.
Add an additional member to mm_walk_ops to indicate locking requirements
for the walk.

Cc: stable@xxxxxxxxxxxxxxx # 6.4.x
Suggested-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxx>
Suggested-by: Jann Horn <jannh@xxxxxxxxxx>
Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
---
arch/powerpc/mm/book3s64/subpage_prot.c | 1 +
arch/riscv/mm/pageattr.c | 1 +
arch/s390/mm/gmap.c | 5 ++++
fs/proc/task_mmu.c | 5 ++++
include/linux/pagewalk.h | 11 ++++++++
mm/damon/vaddr.c | 2 ++
mm/hmm.c | 1 +
mm/ksm.c | 25 ++++++++++-------
mm/madvise.c | 3 +++
mm/memcontrol.c | 2 ++
mm/memory-failure.c | 1 +
mm/mempolicy.c | 22 +++++++++------
mm/migrate_device.c | 1 +
mm/mincore.c | 1 +
mm/mlock.c | 1 +
mm/mprotect.c | 1 +
mm/pagewalk.c | 36 ++++++++++++++++++++++---
mm/vmscan.c | 1 +
18 files changed, 100 insertions(+), 20 deletions(-)

diff --git a/arch/powerpc/mm/book3s64/subpage_prot.c b/arch/powerpc/mm/book3s64/subpage_prot.c
index 0dc85556dec5..ec98e526167e 100644
--- a/arch/powerpc/mm/book3s64/subpage_prot.c
+++ b/arch/powerpc/mm/book3s64/subpage_prot.c
@@ -145,6 +145,7 @@ static int subpage_walk_pmd_entry(pmd_t *pmd, unsigned long addr,

static const struct mm_walk_ops subpage_walk_ops = {
.pmd_entry = subpage_walk_pmd_entry,
+ .walk_lock = PGWALK_WRLOCK_VERIFY,
};

static void subpage_mark_vma_nohuge(struct mm_struct *mm, unsigned long addr,
diff --git a/arch/riscv/mm/pageattr.c b/arch/riscv/mm/pageattr.c
index ea3d61de065b..161d0b34c2cb 100644
--- a/arch/riscv/mm/pageattr.c
+++ b/arch/riscv/mm/pageattr.c
@@ -102,6 +102,7 @@ static const struct mm_walk_ops pageattr_ops = {
.pmd_entry = pageattr_pmd_entry,
.pte_entry = pageattr_pte_entry,
.pte_hole = pageattr_pte_hole,
+ .walk_lock = PGWALK_RDLOCK,
};

static int __set_memory(unsigned long addr, int numpages, pgprot_t set_mask,
diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
index 9c8af31be970..906a7bfc2a78 100644
--- a/arch/s390/mm/gmap.c
+++ b/arch/s390/mm/gmap.c
@@ -2514,6 +2514,7 @@ static int thp_split_walk_pmd_entry(pmd_t *pmd, unsigned long addr,

static const struct mm_walk_ops thp_split_walk_ops = {
.pmd_entry = thp_split_walk_pmd_entry,
+ .walk_lock = PGWALK_WRLOCK_VERIFY,
};

static inline void thp_split_mm(struct mm_struct *mm)
@@ -2565,6 +2566,7 @@ static int __zap_zero_pages(pmd_t *pmd, unsigned long start,

static const struct mm_walk_ops zap_zero_walk_ops = {
.pmd_entry = __zap_zero_pages,
+ .walk_lock = PGWALK_WRLOCK,
};

/*
@@ -2655,6 +2657,7 @@ static const struct mm_walk_ops enable_skey_walk_ops = {
.hugetlb_entry = __s390_enable_skey_hugetlb,
.pte_entry = __s390_enable_skey_pte,
.pmd_entry = __s390_enable_skey_pmd,
+ .walk_lock = PGWALK_WRLOCK,
};

int s390_enable_skey(void)
@@ -2692,6 +2695,7 @@ static int __s390_reset_cmma(pte_t *pte, unsigned long addr,

static const struct mm_walk_ops reset_cmma_walk_ops = {
.pte_entry = __s390_reset_cmma,
+ .walk_lock = PGWALK_WRLOCK,
};

void s390_reset_cmma(struct mm_struct *mm)
@@ -2728,6 +2732,7 @@ static int s390_gather_pages(pte_t *ptep, unsigned long addr,

static const struct mm_walk_ops gather_pages_ops = {
.pte_entry = s390_gather_pages,
+ .walk_lock = PGWALK_RDLOCK,
};

/*
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 507cd4e59d07..ef6ee330e3be 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -758,12 +758,14 @@ static int smaps_hugetlb_range(pte_t *pte, unsigned long hmask,
static const struct mm_walk_ops smaps_walk_ops = {
.pmd_entry = smaps_pte_range,
.hugetlb_entry = smaps_hugetlb_range,
+ .walk_lock = PGWALK_RDLOCK,
};

static const struct mm_walk_ops smaps_shmem_walk_ops = {
.pmd_entry = smaps_pte_range,
.hugetlb_entry = smaps_hugetlb_range,
.pte_hole = smaps_pte_hole,
+ .walk_lock = PGWALK_RDLOCK,
};

/*
@@ -1245,6 +1247,7 @@ static int clear_refs_test_walk(unsigned long start, unsigned long end,
static const struct mm_walk_ops clear_refs_walk_ops = {
.pmd_entry = clear_refs_pte_range,
.test_walk = clear_refs_test_walk,
+ .walk_lock = PGWALK_WRLOCK,
};

static ssize_t clear_refs_write(struct file *file, const char __user *buf,
@@ -1622,6 +1625,7 @@ static const struct mm_walk_ops pagemap_ops = {
.pmd_entry = pagemap_pmd_range,
.pte_hole = pagemap_pte_hole,
.hugetlb_entry = pagemap_hugetlb_range,
+ .walk_lock = PGWALK_RDLOCK,
};

/*
@@ -1935,6 +1939,7 @@ static int gather_hugetlb_stats(pte_t *pte, unsigned long hmask,
static const struct mm_walk_ops show_numa_ops = {
.hugetlb_entry = gather_hugetlb_stats,
.pmd_entry = gather_pte_stats,
+ .walk_lock = PGWALK_RDLOCK,
};

/*
diff --git a/include/linux/pagewalk.h b/include/linux/pagewalk.h
index 27a6df448ee5..27cd1e59ccf7 100644
--- a/include/linux/pagewalk.h
+++ b/include/linux/pagewalk.h
@@ -6,6 +6,16 @@

struct mm_walk;

+/* Locking requirement during a page walk. */
+enum page_walk_lock {
+ /* mmap_lock should be locked for read to stabilize the vma tree */
+ PGWALK_RDLOCK = 0,
+ /* vma will be write-locked during the walk */
+ PGWALK_WRLOCK = 1,
+ /* vma is expected to be already write-locked during the walk */
+ PGWALK_WRLOCK_VERIFY = 2,
+};
+
/**
* struct mm_walk_ops - callbacks for walk_page_range
* @pgd_entry: if set, called for each non-empty PGD (top-level) entry
@@ -66,6 +76,7 @@ struct mm_walk_ops {
int (*pre_vma)(unsigned long start, unsigned long end,
struct mm_walk *walk);
void (*post_vma)(struct mm_walk *walk);
+ enum page_walk_lock walk_lock;
};

/*
diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c
index 2fcc9731528a..e0e59d420fca 100644
--- a/mm/damon/vaddr.c
+++ b/mm/damon/vaddr.c
@@ -386,6 +386,7 @@ static int damon_mkold_hugetlb_entry(pte_t *pte, unsigned long hmask,
static const struct mm_walk_ops damon_mkold_ops = {
.pmd_entry = damon_mkold_pmd_entry,
.hugetlb_entry = damon_mkold_hugetlb_entry,
+ .walk_lock = PGWALK_RDLOCK,
};

static void damon_va_mkold(struct mm_struct *mm, unsigned long addr)
@@ -525,6 +526,7 @@ static int damon_young_hugetlb_entry(pte_t *pte, unsigned long hmask,
static const struct mm_walk_ops damon_young_ops = {
.pmd_entry = damon_young_pmd_entry,
.hugetlb_entry = damon_young_hugetlb_entry,
+ .walk_lock = PGWALK_RDLOCK,
};

static bool damon_va_young(struct mm_struct *mm, unsigned long addr,
diff --git a/mm/hmm.c b/mm/hmm.c
index 855e25e59d8f..277ddcab4947 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -562,6 +562,7 @@ static const struct mm_walk_ops hmm_walk_ops = {
.pte_hole = hmm_vma_walk_hole,
.hugetlb_entry = hmm_vma_walk_hugetlb_entry,
.test_walk = hmm_vma_walk_test,
+ .walk_lock = PGWALK_RDLOCK,
};

/**
diff --git a/mm/ksm.c b/mm/ksm.c
index ba266359da55..00c21fb4d94e 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -455,6 +455,12 @@ static int break_ksm_pmd_entry(pmd_t *pmd, unsigned long addr, unsigned long nex

static const struct mm_walk_ops break_ksm_ops = {
.pmd_entry = break_ksm_pmd_entry,
+ .walk_lock = PGWALK_RDLOCK,
+};
+
+static const struct mm_walk_ops break_ksm_lock_vma_ops = {
+ .pmd_entry = break_ksm_pmd_entry,
+ .walk_lock = PGWALK_WRLOCK,
};

/*
@@ -470,16 +476,17 @@ static const struct mm_walk_ops break_ksm_ops = {
* of the process that owns 'vma'. We also do not want to enforce
* protection keys here anyway.
*/
-static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
+static int break_ksm(struct vm_area_struct *vma, unsigned long addr, bool lock_vma)
{
vm_fault_t ret = 0;
+ const struct mm_walk_ops *ops = lock_vma ?
+ &break_ksm_lock_vma_ops : &break_ksm_ops;

do {
int ksm_page;

cond_resched();
- ksm_page = walk_page_range_vma(vma, addr, addr + 1,
- &break_ksm_ops, NULL);
+ ksm_page = walk_page_range_vma(vma, addr, addr + 1, ops, NULL);
if (WARN_ON_ONCE(ksm_page < 0))
return ksm_page;
if (!ksm_page)
@@ -565,7 +572,7 @@ static void break_cow(struct ksm_rmap_item *rmap_item)
mmap_read_lock(mm);
vma = find_mergeable_vma(mm, addr);
if (vma)
- break_ksm(vma, addr);
+ break_ksm(vma, addr, false);
mmap_read_unlock(mm);
}

@@ -871,7 +878,7 @@ static void remove_trailing_rmap_items(struct ksm_rmap_item **rmap_list)
* in cmp_and_merge_page on one of the rmap_items we would be removing.
*/
static int unmerge_ksm_pages(struct vm_area_struct *vma,
- unsigned long start, unsigned long end)
+ unsigned long start, unsigned long end, bool lock_vma)
{
unsigned long addr;
int err = 0;
@@ -882,7 +889,7 @@ static int unmerge_ksm_pages(struct vm_area_struct *vma,
if (signal_pending(current))
err = -ERESTARTSYS;
else
- err = break_ksm(vma, addr);
+ err = break_ksm(vma, addr, lock_vma);
}
return err;
}
@@ -1029,7 +1036,7 @@ static int unmerge_and_remove_all_rmap_items(void)
if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
continue;
err = unmerge_ksm_pages(vma,
- vma->vm_start, vma->vm_end);
+ vma->vm_start, vma->vm_end, false);
if (err)
goto error;
}
@@ -2530,7 +2537,7 @@ static int __ksm_del_vma(struct vm_area_struct *vma)
return 0;

if (vma->anon_vma) {
- err = unmerge_ksm_pages(vma, vma->vm_start, vma->vm_end);
+ err = unmerge_ksm_pages(vma, vma->vm_start, vma->vm_end, true);
if (err)
return err;
}
@@ -2668,7 +2675,7 @@ int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
return 0; /* just ignore the advice */

if (vma->anon_vma) {
- err = unmerge_ksm_pages(vma, start, end);
+ err = unmerge_ksm_pages(vma, start, end, true);
if (err)
return err;
}
diff --git a/mm/madvise.c b/mm/madvise.c
index 886f06066622..bfe0e06427bd 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -233,6 +233,7 @@ static int swapin_walk_pmd_entry(pmd_t *pmd, unsigned long start,

static const struct mm_walk_ops swapin_walk_ops = {
.pmd_entry = swapin_walk_pmd_entry,
+ .walk_lock = PGWALK_RDLOCK,
};

static void shmem_swapin_range(struct vm_area_struct *vma,
@@ -534,6 +535,7 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,

static const struct mm_walk_ops cold_walk_ops = {
.pmd_entry = madvise_cold_or_pageout_pte_range,
+ .walk_lock = PGWALK_RDLOCK,
};

static void madvise_cold_page_range(struct mmu_gather *tlb,
@@ -757,6 +759,7 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,

static const struct mm_walk_ops madvise_free_walk_ops = {
.pmd_entry = madvise_free_pte_range,
+ .walk_lock = PGWALK_RDLOCK,
};

static int madvise_free_single_vma(struct vm_area_struct *vma,
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index e8ca4bdcb03c..315fd5f45e3c 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6024,6 +6024,7 @@ static int mem_cgroup_count_precharge_pte_range(pmd_t *pmd,

static const struct mm_walk_ops precharge_walk_ops = {
.pmd_entry = mem_cgroup_count_precharge_pte_range,
+ .walk_lock = PGWALK_RDLOCK,
};

static unsigned long mem_cgroup_count_precharge(struct mm_struct *mm)
@@ -6303,6 +6304,7 @@ static int mem_cgroup_move_charge_pte_range(pmd_t *pmd,

static const struct mm_walk_ops charge_walk_ops = {
.pmd_entry = mem_cgroup_move_charge_pte_range,
+ .walk_lock = PGWALK_RDLOCK,
};

static void mem_cgroup_move_charge(void)
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index ece5d481b5ff..6bfb762facab 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -831,6 +831,7 @@ static int hwpoison_hugetlb_range(pte_t *ptep, unsigned long hmask,
static const struct mm_walk_ops hwp_walk_ops = {
.pmd_entry = hwpoison_pte_range,
.hugetlb_entry = hwpoison_hugetlb_range,
+ .walk_lock = PGWALK_RDLOCK,
};

/*
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index c53f8beeb507..ec2eaceffd74 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -718,6 +718,14 @@ static const struct mm_walk_ops queue_pages_walk_ops = {
.hugetlb_entry = queue_folios_hugetlb,
.pmd_entry = queue_folios_pte_range,
.test_walk = queue_pages_test_walk,
+ .walk_lock = PGWALK_RDLOCK,
+};
+
+static const struct mm_walk_ops queue_pages_lock_vma_walk_ops = {
+ .hugetlb_entry = queue_folios_hugetlb,
+ .pmd_entry = queue_folios_pte_range,
+ .test_walk = queue_pages_test_walk,
+ .walk_lock = PGWALK_WRLOCK,
};

/*
@@ -738,7 +746,7 @@ static const struct mm_walk_ops queue_pages_walk_ops = {
static int
queue_pages_range(struct mm_struct *mm, unsigned long start, unsigned long end,
nodemask_t *nodes, unsigned long flags,
- struct list_head *pagelist)
+ struct list_head *pagelist, bool lock_vma)
{
int err;
struct queue_pages qp = {
@@ -749,8 +757,10 @@ queue_pages_range(struct mm_struct *mm, unsigned long start, unsigned long end,
.end = end,
.first = NULL,
};
+ const struct mm_walk_ops *ops = lock_vma ?
+ &queue_pages_lock_vma_walk_ops : &queue_pages_walk_ops;

- err = walk_page_range(mm, start, end, &queue_pages_walk_ops, &qp);
+ err = walk_page_range(mm, start, end, ops, &qp);

if (!qp.first)
/* whole range in hole */
@@ -1078,7 +1088,7 @@ static int migrate_to_node(struct mm_struct *mm, int source, int dest,
vma = find_vma(mm, 0);
VM_BUG_ON(!(flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL)));
queue_pages_range(mm, vma->vm_start, mm->task_size, &nmask,
- flags | MPOL_MF_DISCONTIG_OK, &pagelist);
+ flags | MPOL_MF_DISCONTIG_OK, &pagelist, false);

if (!list_empty(&pagelist)) {
err = migrate_pages(&pagelist, alloc_migration_target, NULL,
@@ -1321,12 +1331,8 @@ static long do_mbind(unsigned long start, unsigned long len,
* Lock the VMAs before scanning for pages to migrate, to ensure we don't
* miss a concurrently inserted page.
*/
- vma_iter_init(&vmi, mm, start);
- for_each_vma_range(vmi, vma, end)
- vma_start_write(vma);
-
ret = queue_pages_range(mm, start, end, nmask,
- flags | MPOL_MF_INVERT, &pagelist);
+ flags | MPOL_MF_INVERT, &pagelist, true);

if (ret < 0) {
err = ret;
diff --git a/mm/migrate_device.c b/mm/migrate_device.c
index 8365158460ed..d5f492356e3e 100644
--- a/mm/migrate_device.c
+++ b/mm/migrate_device.c
@@ -279,6 +279,7 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
static const struct mm_walk_ops migrate_vma_walk_ops = {
.pmd_entry = migrate_vma_collect_pmd,
.pte_hole = migrate_vma_collect_hole,
+ .walk_lock = PGWALK_RDLOCK,
};

/*
diff --git a/mm/mincore.c b/mm/mincore.c
index b7f7a516b26c..dad3622cc963 100644
--- a/mm/mincore.c
+++ b/mm/mincore.c
@@ -176,6 +176,7 @@ static const struct mm_walk_ops mincore_walk_ops = {
.pmd_entry = mincore_pte_range,
.pte_hole = mincore_unmapped_range,
.hugetlb_entry = mincore_hugetlb,
+ .walk_lock = PGWALK_RDLOCK,
};

/*
diff --git a/mm/mlock.c b/mm/mlock.c
index 0a0c996c5c21..479e09d0994c 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -371,6 +371,7 @@ static void mlock_vma_pages_range(struct vm_area_struct *vma,
{
static const struct mm_walk_ops mlock_walk_ops = {
.pmd_entry = mlock_pte_range,
+ .walk_lock = PGWALK_WRLOCK_VERIFY,
};

/*
diff --git a/mm/mprotect.c b/mm/mprotect.c
index 6f658d483704..3aef1340533a 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -568,6 +568,7 @@ static const struct mm_walk_ops prot_none_walk_ops = {
.pte_entry = prot_none_pte_entry,
.hugetlb_entry = prot_none_hugetlb_entry,
.test_walk = prot_none_test,
+ .walk_lock = PGWALK_WRLOCK,
};

int
diff --git a/mm/pagewalk.c b/mm/pagewalk.c
index 2022333805d3..9b2d23fbf4d3 100644
--- a/mm/pagewalk.c
+++ b/mm/pagewalk.c
@@ -400,6 +400,33 @@ static int __walk_page_range(unsigned long start, unsigned long end,
return err;
}

+static inline void process_mm_walk_lock(struct mm_struct *mm,
+ enum page_walk_lock walk_lock)
+{
+ if (walk_lock == PGWALK_RDLOCK)
+ mmap_assert_locked(mm);
+ else
+ mmap_assert_write_locked(mm);
+}
+
+static inline void process_vma_walk_lock(struct vm_area_struct *vma,
+ enum page_walk_lock walk_lock)
+{
+#ifdef CONFIG_PER_VMA_LOCK
+ switch (walk_lock) {
+ case PGWALK_WRLOCK:
+ vma_start_write(vma);
+ break;
+ case PGWALK_WRLOCK_VERIFY:
+ vma_assert_write_locked(vma);
+ break;
+ case PGWALK_RDLOCK:
+ /* PGWALK_RDLOCK is handled by process_mm_walk_lock */
+ break;
+ }
+#endif
+}
+
/**
* walk_page_range - walk page table with caller specific callbacks
* @mm: mm_struct representing the target process of page table walk
@@ -459,7 +486,7 @@ int walk_page_range(struct mm_struct *mm, unsigned long start,
if (!walk.mm)
return -EINVAL;

- mmap_assert_locked(walk.mm);
+ process_mm_walk_lock(walk.mm, ops->walk_lock);

vma = find_vma(walk.mm, start);
do {
@@ -474,6 +501,7 @@ int walk_page_range(struct mm_struct *mm, unsigned long start,
if (ops->pte_hole)
err = ops->pte_hole(start, next, -1, &walk);
} else { /* inside vma */
+ process_vma_walk_lock(vma, ops->walk_lock);
walk.vma = vma;
next = min(end, vma->vm_end);
vma = find_vma(mm, vma->vm_end);
@@ -549,7 +577,8 @@ int walk_page_range_vma(struct vm_area_struct *vma, unsigned long start,
if (start < vma->vm_start || end > vma->vm_end)
return -EINVAL;

- mmap_assert_locked(walk.mm);
+ process_mm_walk_lock(walk.mm, ops->walk_lock);
+ process_vma_walk_lock(vma, ops->walk_lock);
return __walk_page_range(start, end, &walk);
}

@@ -566,7 +595,8 @@ int walk_page_vma(struct vm_area_struct *vma, const struct mm_walk_ops *ops,
if (!walk.mm)
return -EINVAL;

- mmap_assert_locked(walk.mm);
+ process_mm_walk_lock(walk.mm, ops->walk_lock);
+ process_vma_walk_lock(vma, ops->walk_lock);
return __walk_page_range(vma->vm_start, vma->vm_end, &walk);
}

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 1080209a568b..3555927df9b5 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4284,6 +4284,7 @@ static void walk_mm(struct lruvec *lruvec, struct mm_struct *mm, struct lru_gen_
static const struct mm_walk_ops mm_walk_ops = {
.test_walk = should_skip_vma,
.p4d_entry = walk_pud_range,
+ .walk_lock = PGWALK_RDLOCK,
};

int err;
--
2.41.0.585.gd2178a4bd4-goog