kernel - SMP - "Fix AP #%d (PHY# %d) failed" issues

kernel - SMP - "Fix AP #%d (PHY# %d) failed" issues

Ok, here's what is going on.  If an SMI interrupt occurs while
an AP is going through the INIT/STARTUP IPI sequence the AP will
brick, and nothing you do will resurrect it.

BIOSes typically set up SMI interrupts when emulating (for example)
a PS/2 keyboard with a USB keyboard, or even if just implementing
BIOS support for a USB keyboard.  Even worse, the BIOS may set up
the interrupt to poll at 1000hz.  And, EVEN WORSE, it can totally
depend on which USB port you've plugged your keyboard in.  And, on top
of all of that, the SMI interrupt is not consistent.

The INIT/STARTUP code contains a 10ms delay (as per Intel spec) between
the INIT IPI and the STARTUP IPI.  Well, you can do the math.

In order to reliably boot a SMP system where the BIOS has set up
SMI interrupts this patch uses a nifty bit of code to detect when
the SMI interrupt has occurred and tries to shift the INIT/STARTUP
sequence into a gap between SMI interrupts.  If it has to it will
reduce the 10ms spec delay all the way down to 150us.  In many
cases we really have no choice for reliable operation.  Even a 300uS
delay is too much in the tests I performed on a Shuttle Phenom and
Phenom II cube.  I don't honestly know if this will break other SMP
configurations, we'll have to see.

On the particular shuttle I tested on, one of the four USB connections
on the backpanel (the upper left when looking at it from the back)
seemed to cause the BIOS to set up SMI interrupts at a high rate and
caused kernel boots to fail.  With this commit those boots now succeed.