There is a bug in copy_page_range with 4 level page table change. 
copy_page_range do a continue without adding pgds and addr when
pgd_none(*src_pgd) or pgd_bad(*src_pgd).
Signed-off-by: Zou Nan hai <nanhai.zou@intel.com>
Acked-by: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>