[PATCH v7 2/4] mm/rmap: add helper to restart pgtable walk on changes

[Lance Yang <ioworker0@gmail.com>]

Introduce the page_vma_mapped_walk_restart() helper to handle scenarios
where the page table walk needs to be restarted due to changes in the page
table, such as when a PMD is split. It releases the PTL held during the
previous walk and resets the state, allowing a new walk to start at the
current address stored in pvmw->address.

Suggested-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Lance Yang <ioworker0@gmail.com>
---
 include/linux/rmap.h | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 7229b9baf20d..5f18509610cc 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -710,6 +710,28 @@ static inline void page_vma_mapped_walk_done(struct page_vma_mapped_walk *pvmw)
 		spin_unlock(pvmw->ptl);
 }
 
+/**
+ * page_vma_mapped_walk_restart - Restart the page table walk.
+ * @pvmw: Pointer to struct page_vma_mapped_walk.
+ *
+ * It restarts the page table walk when changes occur in the page
+ * table, such as splitting a PMD. Ensures that the PTL held during
+ * the previous walk is released and resets the state to allow for
+ * a new walk starting at the current address stored in pvmw->address.
+ */
+static inline void
+page_vma_mapped_walk_restart(struct page_vma_mapped_walk *pvmw)
+{
+	WARN_ON_ONCE(!pvmw->pmd);
+	WARN_ON_ONCE(!pvmw->ptl);
+
+	if (pvmw->ptl)
+		spin_unlock(pvmw->ptl);
+
+	pvmw->ptl = NULL;
+	pvmw->pmd = NULL;
+}
+
 bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw);
 
 /*
-- 
2.33.1