Re: [Xen-devel] [PATCH] MSR related clean up

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 24/06/2009 10:21, "Sheng Yang" <sheng@xxxxxxxxxxxxxxx> wrote:

> What we suffered now is, there are some MSRs existed in CPU, but shouldn't be
> accessed by guest. And guest should expected a GP fault for accessing, but we
> return a real value, which is not desired at all.
>
> And in general, reading from unknown native MSR is dangerous, and also break
> host/guest isolation. I think we at least should control what we read from
> native. Maybe add more MSR handling is necessary.

I kind of agree with you, up to but not including delivering #GPs that would
not be delivered when running the guest OS natively. A middle ground might
be to return all zeros for unknown MSRs for which rdmsr_safe() succeeds.
That is by far the most popular bodge value we manually use to fix up cases
where returning the real MSR value was actually a proven problem.

 -- Keir



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