MIPS: highmem: ensure that we don't use more than one page for PTEs

All PTEs used by PKMAP should be allocated in a contiguous memory area,
but we do not currently have a mechanism to enforce that, so ensure that
we don't try to allocate more entries than would fit in a single page.

Current fixed value of 1024 would not work with XPA enabled when
sizeof(pte_t)==8 and we need two pages to store pte tables.
Signed-off-by: Marcin Nowakowski <marcin.nowakowski@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/15949/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/include/asm/highmem.h

@@ -35,7 +35,12 @@ extern pte_t *pkmap_page_table;
  * easily, subsequent pte tables have to be allocated in one physical
  * chunk of RAM.
  */
+#ifdef CONFIG_PHYS_ADDR_T_64BIT
+#define LAST_PKMAP 512
+#else
 #define LAST_PKMAP 1024
+#endif
+
 #define LAST_PKMAP_MASK (LAST_PKMAP-1)
 #define PKMAP_NR(virt)	((virt-PKMAP_BASE) >> PAGE_SHIFT)
 #define PKMAP_ADDR(nr)	(PKMAP_BASE + ((nr) << PAGE_SHIFT))