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

[Sheng Yang <sheng@xxxxxxxxxxxxxxx>]

On Wednesday 24 June 2009 17:03:56 Keir Fraser wrote:
> On 24/06/2009 09:50, "Sheng Yang" <sheng@xxxxxxxxxxxxxxx> wrote:
> > On Thursday 18 June 2009 17:57:06 Sheng Yang wrote:
> >> rdmsr_safe() is used to access MSR unknown to Xen, and is not safe... I
> >> think it is legacy.
> >>
> >> Also let msr_write be parity with msr_read on MSR_IA32_MISC_ENABLE.
> >>
> >> CC: Eddie Dong <eddie.dong@xxxxxxxxx>
> >> Signed-off-by: Sheng Yang <sheng@xxxxxxxxxxxxxxx>
> >
> > Keir?
>
> Looks pretty dangerous to me. So I'm not sure. There are various MSRs that
> are detected via CPU family/model (which we pass through) which would then
> #GP on access. Also this doesn't change the AMD default. Overall, what we
> have now does seem to work so I'm reluctant to mess with it.
>
Hi Keir

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.

-- 
regards
Yang, Sheng

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