v4.19.13 snapshot.
diff --git a/include/linux/pfn.h b/include/linux/pfn.h
new file mode 100644
index 0000000..14bc053
--- /dev/null
+++ b/include/linux/pfn.h
@@ -0,0 +1,24 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_PFN_H_
+#define _LINUX_PFN_H_
+
+#ifndef __ASSEMBLY__
+#include <linux/types.h>
+
+/*
+ * pfn_t: encapsulates a page-frame number that is optionally backed
+ * by memmap (struct page). Whether a pfn_t has a 'struct page'
+ * backing is indicated by flags in the high bits of the value.
+ */
+typedef struct {
+ u64 val;
+} pfn_t;
+#endif
+
+#define PFN_ALIGN(x) (((unsigned long)(x) + (PAGE_SIZE - 1)) & PAGE_MASK)
+#define PFN_UP(x) (((x) + PAGE_SIZE-1) >> PAGE_SHIFT)
+#define PFN_DOWN(x) ((x) >> PAGE_SHIFT)
+#define PFN_PHYS(x) ((phys_addr_t)(x) << PAGE_SHIFT)
+#define PHYS_PFN(x) ((unsigned long)((x) >> PAGE_SHIFT))
+
+#endif