[v2 PATCH] mm: dax: add comment for PFN_SPECIAL

[Yang Shi]

The comment for PFN_SPECIAL is missed in pfn_t.h. Add comment to get
consistent with other pfn flags.

Suggested-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Signed-off-by: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
---
v2: rephrase the comment per Dan

 include/linux/pfn_t.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/include/linux/pfn_t.h b/include/linux/pfn_t.h
index 21713dc..d6cc4b5 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))
-- 
1.8.3.1