kdb=early broken on some newer machines

[Martin Hicks <mort@xxxxxxx>]

I don't have a good handle on what class of machines kdb=early does not
work on.  It seems that newer machines, particularly all the
nehalem machines that I have access to, do not work.

KDB is entered correctly, but keyboard input does not function.  I'll
try to track this down as quickly as I can, but if others have any ideas
about why this may not work, then I'd like to hear about it.

Thanks,
mh