diff --git a/mm/nommu.c b/mm/nommu.c
index 2fd2ad5..598bc87 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -240,6 +240,27 @@
 }
 EXPORT_SYMBOL(get_user_pages);
 
+/**
+ * follow_pfn - look up PFN at a user virtual address
+ * @vma: memory mapping
+ * @address: user virtual address
+ * @pfn: location to store found PFN
+ *
+ * Only IO mappings and raw PFN mappings are allowed.
+ *
+ * Returns zero and the pfn at @pfn on success, -ve otherwise.
+ */
+int follow_pfn(struct vm_area_struct *vma, unsigned long address,
+	unsigned long *pfn)
+{
+	if (!(vma->vm_flags & (VM_IO | VM_PFNMAP)))
+		return -EINVAL;
+
+	*pfn = address >> PAGE_SHIFT;
+	return 0;
+}
+EXPORT_SYMBOL(follow_pfn);
+
 DEFINE_RWLOCK(vmlist_lock);
 struct vm_struct *vmlist;