ptos: pm: Add page frame conversion helpers

Signed-off-by: Chloe M <chloe@mensia.org>

service/ptos/head/mm/pm.h

@@ -0,0 +1,27 @@
+/*
+ * Copyright (c) 2026, Chloe M.
+ * Provided under the BSD-3 clause.
+ *
+ * Description: Physical memory management
+ * Author:      Chloe M.
+ */
+
+#ifndef _MM_PM_H_
+#define _MM_PM_H_ 1
+
+#include <ptdef.h>
+#include <hal/page.h>
+
+/* Page frame number type */
+typedef USIZE MM_PFN;
+
+/*
+ * These macros allow the conversion of page frame numbers
+ * to physical addresses and vice versa.
+ */
+#define PFN_TO_ADDRESS(PFN) \
+    ((PFN) << LOG2_PAGESIZE)
+#define ADDRESS_TO_PFN(ADDR) \
+    ((ADDR) >> LOG2_PAGESIZE)
+
+#endif  /* !_MM_PM_H_ */