The attached patch adds the capability for dom0 to inject MCA errors 
into Xen. The basic idea is to add specific MSR values that will be read 
by the polling code or the #MC handler. On AMD cpus, the MSRs can 
actually be written, on Intel CPUs, interpose code is used to fake the 
MSR values.

Since actual hardware problems are rare, it's convenient to be able to 
test the code like this. We run our testsuite using this code. Others 
have expressed some interest in this, so that's why I'm submitting this 
patch.

- Frank