While discussing races in the NMI handler's trailer fiddling with RTC
registers, I've discovered we incorrectly attempt to handle NMIs coming
from the system (memory errors, IOCHK# assertions, etc.) with all
processors even though the interrupts are only routed to the bootstrap
processor.  If one of these events coincides with a NMI watchdog tick it
may even be handled multiple times in parallel.

Here is a fix that makes application processors ignore these events.  They
no longer access the NMI status bits at I/O port 0x61 which has also the
advantage of removing the contention on the port when the I/O APIC NMI
watchdog makes all processors arrive at the handler at the same time.
Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>