vma->vm_page_prot is read lockless from the rmap_walk, it may be
updated concurrently and this prevents the risk of reading
intermediate values.
Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>
---
mm/huge_memory.c | 2 +-
mm/migrate.c | 2 +-
mm/mmap.c | 9 ++++++---
3 files changed, 8 insertions(+), 5 deletions(-)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index cb95a83..995f8a1 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1566,7 +1566,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
if (soft_dirty)
entry = pte_swp_mksoft_dirty(entry);
} else {
- entry = mk_pte(page + i, vma->vm_page_prot);
+ entry = mk_pte(page + i, READ_ONCE(vma->vm_page_prot));
entry = maybe_mkwrite(entry, vma);
if (!write)
entry = pte_wrprotect(entry);
diff --git a/mm/migrate.c b/mm/migrate.c
index 00167df..e49ccce 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -234,7 +234,7 @@ static int remove_migration_pte(struct page *new, struct vm_area_struct *vma,
goto unlock;
get_page(new);
- pte = pte_mkold(mk_pte(new, vma->vm_page_prot));
+ pte = pte_mkold(mk_pte(new, READ_ONCE(vma->vm_page_prot)));
if (pte_swp_soft_dirty(*ptep))
pte = pte_mksoft_dirty(pte);
diff --git a/mm/mmap.c b/mm/mmap.c
index c34f643..1abf106 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -112,13 +112,16 @@ static pgprot_t vm_pgprot_modify(pgprot_t oldprot, unsigned long vm_flags)
void vma_set_page_prot(struct vm_area_struct *vma)
{
unsigned long vm_flags = vma->vm_flags;
+ pgprot_t vm_page_prot;
- vma->vm_page_prot = vm_pgprot_modify(vma->vm_page_prot, vm_flags);
+ vm_page_prot = vm_pgprot_modify(vma->vm_page_prot, vm_flags);
if (vma_wants_writenotify(vma)) {
vm_flags &= ~VM_SHARED;
- vma->vm_page_prot = vm_pgprot_modify(vma->vm_page_prot,
- vm_flags);
+ vm_page_prot = vm_pgprot_modify(vma->vm_page_prot,
+ vm_flags);
}
+ /* remove_protection_ptes reads vma->vm_page_prot without mmap_sem */
+ WRITE_ONCE(vma->vm_page_prot, vm_page_prot);
}
static unsigned long vm_mergeable __read_mostly;
--
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