The following patch reworks the MCA error telemetry handling inside Xen, 
  and shares code between the Intel and AMD implementations as much as 
possible.

I've had this patch sitting around for a while, but it wasn't ported to 
-unstable yet. I finished porting and testing it, and am submitting it 
now, because the Intel folks want to go ahead and submit their new 
changes, so we agreed that I should push our changes first.

Brief explanation of the telemetry part: previously, the telemetry was 
accessed in a global array, with index variables used to access it. 
There were some issues with that: race conditions with regard to new 
machine checks (or CMCIs) coming in while handling the telemetry, and 
interaction with domains having been notified or not, which was a bit 
hairy. Our changes (I should say: Gavin Maltby's changes, as he did the 
bulk of this work for our 3.1 based tree, I merely ported/extended it to 
3.3 and beyond) make telemetry access transactional (think of a 
database). Also, the internal database updates are atomic, since the 
final commit is done by a pointer swap. There is a brief explanation of 
the mechanism in mctelem.h.This patch also removes dom0->domU 
notification, which is ok, since Intel's upcoming changes will replace 
domU notification with a vMCE mechanism anyway.

The common code part is pretty much what it says. It defines a common 
MCE handler, with a few hooks for the special needs of the specific CPUs.

I've been told that Intel's upcoming patch will need to make some parts 
of the common code specific to the Intel CPU again, but we'll work 
together to use as much common code as possible.

- Frank