[patch 073/262] mm: clear vmf->pte after pte_unmap_same() returns

Andrew Morton
2021-11-05T20:38:31Z

From: Peter Xu <peterx@redhat.com>
Subject: mm: clear vmf->pte after pte_unmap_same() returns

pte_unmap_same() will always unmap the pte pointer. After the unmap,
vmf->pte will not be valid any more, we should clear it.

It was safe only because no one is accessing vmf->pte after
pte_unmap_same() returns, since the only caller of pte_unmap_same() (so
far) is do_swap_page(), where vmf->pte will in most cases be overwritten
very soon.

Directly pass in vmf into pte_unmap_same() and then we can also avoid the
long parameter list too, which should be a nice cleanup.

Link: https://lkml.kernel.org/r/20210915181533.11188-1-peterx@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Liam Howlett <liam.howlett@oracle.com>
Acked-by: Hugh Dickins <hughd@google.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: "Kirill A . Shutemov" <kirill@shutemov.name>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

mm/memory.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)

--- a/mm/memory.c~mm-clear-vmf-pte-after-pte_unmap_same-returns
+++ a/mm/memory.c
@@ -2728,19 +2728,19 @@ EXPORT_SYMBOL_GPL(apply_to_existing_page
* proceeding (but do_wp_page is only called after already making such a check;
* and do_anonymous_page can safely check later on).
*/
-static inline int pte_unmap_same(struct mm_struct *mm, pmd_t *pmd,
- pte_t *page_table, pte_t orig_pte)
+static inline int pte_unmap_same(struct vm_fault *vmf)
{
int same = 1;
#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPTION)
if (sizeof(pte_t) > sizeof(unsigned long)) {
- spinlock_t *ptl = pte_lockptr(mm, pmd);
+ spinlock_t *ptl = pte_lockptr(vmf->vma->vm_mm, vmf->pmd);
spin_lock(ptl);
- same = pte_same(*page_table, orig_pte);
+ same = pte_same(*vmf->pte, vmf->orig_pte);
spin_unlock(ptl);
}
#endif
- pte_unmap(page_table);
+ pte_unmap(vmf->pte);
+ vmf->pte = NULL;
return same;
}

@@ -3492,7 +3492,7 @@ vm_fault_t do_swap_page(struct vm_fault
vm_fault_t ret = 0;
void *shadow = NULL;

- if (!pte_unmap_same(vma->vm_mm, vmf->pmd, vmf->pte, vmf->orig_pte))
+ if (!pte_unmap_same(vmf))
goto out;

entry = pte_to_swp_entry(vmf->orig_pte);
_