1 files changed, 24 insertions, 0 deletions
diff --git a/mm/gup.c b/mm/gup.c
index ad0c8922dac3..2b84eead9baa 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -3760,3 +3760,27 @@ err:
 	return ret;
 }
 EXPORT_SYMBOL_GPL(memfd_pin_folios);
+
+/**
+ * folio_add_pins() - add pins to an already-pinned folio
+ * @folio: the folio to add more pins to
+ * @pins: number of pins to add
+ *
+ * Try to add more pins to an already-pinned folio. The semantics
+ * of the pin (e.g., FOLL_WRITE) follow any existing pin and cannot
+ * be changed.
+ *
+ * This function is helpful when having obtained a pin on a large folio
+ * using memfd_pin_folios(), but wanting to logically unpin parts
+ * (e.g., individual pages) of the folio later, for example, using
+ * unpin_user_page_range_dirty_lock().
+ *
+ * This is not the right interface to initially pin a folio.
+ */
+int folio_add_pins(struct folio *folio, unsigned int pins)
+{
+	VM_WARN_ON_ONCE(!folio_maybe_dma_pinned(folio));
+
+	return try_grab_folio(folio, pins, FOLL_PIN);
+}
+EXPORT_SYMBOL_GPL(folio_add_pins);