diff --git a/include/linux/pfn_t.h b/include/linux/pfn_t.h
index 673546ba7342..7bb77850c65a 100644
--- a/include/linux/pfn_t.h
+++ b/include/linux/pfn_t.h
@@ -9,6 +9,8 @@
  * PFN_SG_LAST - pfn references a page and is the last scatterlist entry
  * PFN_DEV - pfn is not covered by system memmap by default
  * PFN_MAP - pfn has a dynamic page mapping established by a device driver
+ * PFN_SPECIAL - for CONFIG_FS_DAX_LIMITED builds to allow XIP, but not
+ *		 get_user_pages
  */
 #define PFN_FLAGS_MASK (((u64) (~PAGE_MASK)) << (BITS_PER_LONG_LONG - PAGE_SHIFT))
 #define PFN_SG_CHAIN (1ULL << (BITS_PER_LONG_LONG - 1))