-/* Page table (bits 12:21). */
-#define PTSHIFT PGBITS /* First page table bit. */
-#define PTBITS 10 /* Number of page table bits. */
-#define PTMASK MASK(PTSHIFT, PTBITS)
+/* Page table (bits 12:22). */
+#define PTSHIFT PGBITS /* Index of first page table bit. */
+#define PTBITS 10 /* Number of page table bits. */
+#define PTMASK MASK(PTSHIFT, PTBITS) /* Page table bits (12:22). */
+#define PTSPAN (1 << PTBITS << PGBITS) /* Bytes covered by a page table. */