The attached patch implements a way to request to receive an NMI if it 
comes from an otherwise unknown source.  I needed this for handling NMIs 
with the IPMI watchdog.  This function was discussed a little a while 
back on the mailing list, but nothing was done about it, so I 
implemented a request/release for NMIs.  The code is in 
arch/i386/kernel/traps.c, but it's pretty generic and could possibly 
live in kernel.  I'm not sure, though.

This is relative to 2.5.44.  I have a 2.4 version of it, too.

-Corey