From: Bodo Stroesser

To make the vsyscall-page available for copy_from_user() and
ptrace(), we should use kernel's "gate-vma" mechanism.
Therefore we need a valid page structure. To have this, one
page (or more) is allocated at boot time, the contents of the
vsyscall-page is copied into this page and the page's pte is
inserted in swapper's pagetables.
Now it will be copied into the pagetables of all processes.

Note: this alone doesn't work, since FIXADDR_USER_START and
      FIXADDR_USER_END are not yet defined correctly. Also
      access_ok_skas() does not yet grant read accesses to
      pages not in the normal user area.

Risks:
Please check the first hunk! I don't know, whether this change is OK.
Maybe fixrange_init() is wrong anyway with 3-level-pagetables?

Here access_ok_skas() and FIXADDR_USER_XXXX are fixed.
Now everything should work fine, while the processes are
running. But if a process crashes, the vsyscall-page will
not be dumped.
Signed-off-by: Bodo Stroesser <bodo.stroesser@fujitsu-siemens.com>
Signed-off-by: Jeff Dike <jdike@addtoit.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>