x86, 64bit, mm: Make pgd next calculation consistent with pud/pmd

Just like the way we calculate next for pud and pmd, aka round down and
add size.

Also, do not do boundary-checking with 'next', and just pass 'end' down
to phys_pud_init() instead. Because the loop in phys_pud_init() stops at
PTRS_PER_PUD and thus can handle a possibly bigger 'end' properly.

Signed-off-by: Yinghai Lu <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: H. Peter Anvin <[e-mail]>

arch/x86/mm/init_64.c

···
 		pgd_t *pgd = pgd_offset_k(start);
 		pud_t *pud;
 
-		next = (start + PGDIR_SIZE) & PGDIR_MASK;
-		if (next > end)
-			next = end;
+		next = (start & PGDIR_MASK) + PGDIR_SIZE;
 
 		if (pgd_val(*pgd)) {
 			pud = (pud_t *)pgd_page_vaddr(*pgd);
···
 		}
 
 		pud = alloc_low_page();
-		last_map_addr = phys_pud_init(pud, __pa(start), __pa(next),
+		last_map_addr = phys_pud_init(pud, __pa(start), __pa(end),
 						 page_size_mask);
 
 		spin_lock(&init_mm.page_table_lock);