[PATCH 16/16] mm/migration: fix potential pte_unmap on an not mapped pte

[Miaohe Lin]

__migration_entry_wait and migration_entry_wait_on_locked assume pte is
always mapped from caller. But this is not the case when it's called from
migration_entry_wait_huge and follow_huge_pmd. And a parameter unmap to
indicate whether pte needs to be unmapped to fix this issue.

Fixes: 30dad30922cc ("mm: migration: add migrate_entry_wait_huge()")
Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
---
 include/linux/migrate.h |  2 +-
 include/linux/swapops.h |  4 ++--
 mm/filemap.c            | 10 +++++-----
 mm/hugetlb.c            |  2 +-
 mm/migrate.c            | 14 ++++++++------
 5 files changed, 17 insertions(+), 15 deletions(-)

diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index 66a34eae8cb6..3ef4ff699bef 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -41,7 +41,7 @@ extern int migrate_huge_page_move_mapping(struct address_space *mapping,
 extern int migrate_page_move_mapping(struct address_space *mapping,
 		struct page *newpage, struct page *page, int extra_count);
 void migration_entry_wait_on_locked(swp_entry_t entry, pte_t *ptep,
-				spinlock_t *ptl);
+				spinlock_t *ptl, bool unmap);
 void folio_migrate_flags(struct folio *newfolio, struct folio *folio);
 void folio_migrate_copy(struct folio *newfolio, struct folio *folio);
 int folio_migrate_mapping(struct address_space *mapping,
diff --git a/include/linux/swapops.h b/include/linux/swapops.h
index d356ab4047f7..d66556875d7d 100644
--- a/include/linux/swapops.h
+++ b/include/linux/swapops.h
@@ -213,7 +213,7 @@ static inline swp_entry_t make_writable_migration_entry(pgoff_t offset)
 }
 
 extern void __migration_entry_wait(struct mm_struct *mm, pte_t *ptep,
-					spinlock_t *ptl);
+					spinlock_t *ptl, bool unmap);
 extern void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
 					unsigned long address);
 extern void migration_entry_wait_huge(struct vm_area_struct *vma,
@@ -235,7 +235,7 @@ static inline int is_migration_entry(swp_entry_t swp)
 }
 
 static inline void __migration_entry_wait(struct mm_struct *mm, pte_t *ptep,
-					spinlock_t *ptl) { }
+					spinlock_t *ptl, bool unmap) { }
 static inline void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
 					 unsigned long address) { }
 static inline void migration_entry_wait_huge(struct vm_area_struct *vma,
diff --git a/mm/filemap.c b/mm/filemap.c
index 8f7e6088ee2a..18c353d52aae 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1389,6 +1389,7 @@ static inline int folio_wait_bit_common(struct folio *folio, int bit_nr,
  * @ptep: mapped pte pointer. Will return with the ptep unmapped. Only required
  *        for pte entries, pass NULL for pmd entries.
  * @ptl: already locked ptl. This function will drop the lock.
+ * @unmap: indicating whether ptep need to be unmapped.
  *
  * Wait for a migration entry referencing the given page to be removed. This is
  * equivalent to put_and_wait_on_page_locked(page, TASK_UNINTERRUPTIBLE) except
@@ -1402,7 +1403,7 @@ static inline int folio_wait_bit_common(struct folio *folio, int bit_nr,
  * there.
  */
 void migration_entry_wait_on_locked(swp_entry_t entry, pte_t *ptep,
-				spinlock_t *ptl)
+				spinlock_t *ptl, bool unmap)
 {
 	struct wait_page_queue wait_page;
 	wait_queue_entry_t *wait = &wait_page.wait;
@@ -1439,10 +1440,9 @@ void migration_entry_wait_on_locked(swp_entry_t entry, pte_t *ptep,
 	 * a valid reference to the page, and it must take the ptl to remove the
 	 * migration entry. So the page is valid until the ptl is dropped.
 	 */
-	if (ptep)
-		pte_unmap_unlock(ptep, ptl);
-	else
-		spin_unlock(ptl);
+	spin_unlock(ptl);
+	if (unmap && ptep)
+		pte_unmap(ptep);
 
 	for (;;) {
 		unsigned int flags;
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 07668781c246..8088128c25db 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -6713,7 +6713,7 @@ follow_huge_pmd(struct mm_struct *mm, unsigned long address,
 	} else {
 		if (is_hugetlb_entry_migration(pte)) {
 			spin_unlock(ptl);
-			__migration_entry_wait(mm, (pte_t *)pmd, ptl);
+			__migration_entry_wait(mm, (pte_t *)pmd, ptl, false);
 			goto retry;
 		}
 		/*
diff --git a/mm/migrate.c b/mm/migrate.c
index 98a968e6f465..5519261f54fe 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -281,7 +281,7 @@ void remove_migration_ptes(struct folio *src, struct folio *dst, bool locked)
  * When we return from this function the fault will be retried.
  */
 void __migration_entry_wait(struct mm_struct *mm, pte_t *ptep,
-				spinlock_t *ptl)
+				spinlock_t *ptl, bool unmap)
 {
 	pte_t pte;
 	swp_entry_t entry;
@@ -295,10 +295,12 @@ void __migration_entry_wait(struct mm_struct *mm, pte_t *ptep,
 	if (!is_migration_entry(entry))
 		goto out;
 
-	migration_entry_wait_on_locked(entry, ptep, ptl);
+	migration_entry_wait_on_locked(entry, ptep, ptl, unmap);
 	return;
 out:
-	pte_unmap_unlock(ptep, ptl);
+	spin_unlock(ptl);
+	if (unmap)
+		pte_unmap(ptep);
 }
 
 void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
@@ -306,14 +308,14 @@ void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
 {
 	spinlock_t *ptl = pte_lockptr(mm, pmd);
 	pte_t *ptep = pte_offset_map(pmd, address);
-	__migration_entry_wait(mm, ptep, ptl);
+	__migration_entry_wait(mm, ptep, ptl, true);
 }
 
 void migration_entry_wait_huge(struct vm_area_struct *vma,
 		struct mm_struct *mm, pte_t *pte)
 {
 	spinlock_t *ptl = huge_pte_lockptr(hstate_vma(vma), mm, pte);
-	__migration_entry_wait(mm, pte, ptl);
+	__migration_entry_wait(mm, pte, ptl, false);
 }
 
 #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
@@ -324,7 +326,7 @@ void pmd_migration_entry_wait(struct mm_struct *mm, pmd_t *pmd)
 	ptl = pmd_lock(mm, pmd);
 	if (!is_pmd_migration_entry(*pmd))
 		goto unlock;
-	migration_entry_wait_on_locked(pmd_to_swp_entry(*pmd), NULL, ptl);
+	migration_entry_wait_on_locked(pmd_to_swp_entry(*pmd), NULL, ptl, false);
 	return;
 unlock:
 	spin_unlock(ptl);
-- 
2.23.0