diff --git a/mm/highmem.c b/mm/highmem.c
index 51e1c19..be8f8d3 100644
--- a/mm/highmem.c
+++ b/mm/highmem.c
@@ -99,6 +99,15 @@
 	flush_tlb_kernel_range(PKMAP_ADDR(0), PKMAP_ADDR(LAST_PKMAP));
 }
 
+/* Flush all unused kmap mappings in order to remove stray
+   mappings. */
+void kmap_flush_unused(void)
+{
+	spin_lock(&kmap_lock);
+	flush_all_zero_pkmaps();
+	spin_unlock(&kmap_lock);
+}
+
 static inline unsigned long map_new_virtual(struct page *page)
 {
 	unsigned long vaddr;