From Terence Ripperda <tripperda@nvidia.com>

When doing iounmap don't try to change_page_attr back the guard
page that ioremap added.

Since the last round of change_page_attr changes this would
trigger an BUG because the reference count on the changed pages
wouldn't match up.

The problem would be only visible on machines with >3GB of memory,
because only then the PCI memory hole is below end_pfn and
change_page_attr is used.

Fixed for both i386 and x86-64.

This was actually discovered&fixed by Andrea earlier, but I goofed up
while doing the last ioremap fixes merge and this change got lost.
Poor Terence had to debug it again. Sorry about that.

cc: andrea@suse.de
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>