x86: fix kernel_physical_mapping_init() for large x86 systems

based on e22146e6 upstream

Fix bug in kernel_physical_mapping_init() that causes kernel
page table to be built incorrectly for systems with greater
than 512GB of memory.
Signed-off-by: Jack Steiner <steiner@sgi.com>
Cc: linux-mm@kvack.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Cc: Oliver Pinter <oliver.pntr@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

arch/x86/mm/init_64.c

@@ -579,7 +579,7 @@ unsigned long __init_refok init_memory_mapping(unsigned long start, unsigned lon
 		else
 			pud = alloc_low_page(&pud_phys);
 
-		next = start + PGDIR_SIZE;
+		next = (start + PGDIR_SIZE) & PGDIR_MASK;
 		if (next > end)
 			next = end;
 		last_map_addr = phys_pud_init(pud, __pa(start), __pa(next));