Re: [Xen-devel] machine check support in HVM guests

["Jan Beulich" <jbeulich@xxxxxxxxxx>]

Oh, btw., are you implicitly telling me that forcing a GP fault on reads
(and ideally also writes) of invalid MSRs then is also impossible? That
is what I'm in the process of adding, at least for the case where Xen
itself also receives a GP fault when reading the respective physical
MSR.

Jan

>>> Keir Fraser <keir@xxxxxxxxxxxxx> 27.11.06 14:27 >>>
On 27/11/06 12:29, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:

> Neither SVM nor VMX suppress CPUID[1].EDX.MC{E,A}, but there also is no
> virtualization of the respective MSRs. Since the latter seems to have at best
> marginal usefulness, shouldn't CPUID be respectively updated?

Virtualisation of CPUID is currently back-to-front imo. We should be
supplying an entirely fake CPUID space, filled in with native info only in
places where that makes sense. Instead we supply native info, replaced with
virtualised alternatives where that turns out to be needed. This, for
example, means we cannot guarantee to support HVM guests with current Xen on
future processors. They may extend the CPUID space in a way that current Xen
does not understand and cause guests to try to use features that Xen does
not virtualise or emulate.

For your specific question, MCE/MCA used to be removed but 64-bit Windows
requires this feature to be available (not sure if it's just for WHQL
though). So we should emulate some basic MC support; enough to accept and
discard MSR programming at least.

 -- Keir


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