When I made get_user_pages support looking up a pte for the "gate" area, I
assumed it would be part of the kernel's fixed mappings.  On x86-64 running
a 32-bit task, the 32-bit vsyscall DSO page still has no vma but has its
pte allocated in the user mm in the normal fashion.  This patch makes it
use the generic page-table lookup calls rather than the shortcuts.
With this, ptrace on x86-64 can access a 32-bit process's vsyscall page.

The behavior on x86 is unchanged.
Signed-off-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>