Re: [Xen-devel] Porting of Guest OS

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

> 
> 
> On Thu, 30 Dec 2004, Amitabh Tamhane wrote:
> 
> > During boot-up:
> > 1) Applying Intel IA32 Microcode update: insmod:
> > /lib/modules/2.6.5-7.97-smp/kernel/arch/i386/kernel/microcode.o: insmod
> > char-major-10-184 failed

That's the wrong module anyway -- it's from a native kernel not a
Xen-ported kernel.

> is it safe to assume that code in Ring 1 can't upgrade microcode :-)?
> I'd say that the microcode module would surprise me if it worked. 
> 
> ron

A privileged domain can use the RDMSR/WRMSR Xen functions. In the
unstable tree it can even execute RDMSR/WRMSR directly and Xen will
emulate them.

The main difficulty is that currently we only execute the MSR accesses
on the CPU on which the domain is running. We could easily change the
default to be to write to all CPUs -- that would make more sense for
microcode updates, but I'm not sure if it would be silly for other
things. 

The other difficulty is that a microcode update needs several MSR
updates per CPU that need to happen with no other overlapping
updates.

The microcode driver is pretty small, so we may end up putting it in
Xen, as we did with the MTRR code. 

 -- Keir


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