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Re: [Xen-devel] mce_wrmsr() and (at least) HVM guests

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Subject: Re: [Xen-devel] mce_wrmsr() and (at least) HVM guests
From: "James (song wei)" <jsong@xxxxxxxxxx>
Date: Tue, 1 Dec 2009 22:18:12 -0800 (PST)
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IMO, mce_wrmsr() shouldn't return -1 as a workaround, which leads to a #GP
in the
guest, at lease in MSR_IA32_MCG_CTL writting. Pnerhaps, it happens with
IOMMU ad the GART.

-James Song (wei)

Jan Beulich wrote:
> With mce_wrmsr() not permitting to write other than all zeroes or all ones
> to MCG_CTL and MCn_CTL, it is not possible for guests to implement
> workarounds (see the one in mce_cpu_quirks() which has been present in
> Linux versions for a very long time). While one could expect PV guests to
> be aware of that (and avoid the workaround), HVM guests clearly can't
> be expected to. Thus the question is whether the handling should be
> made a little more permissive.
> Initially I had thought of just making Xen check whether the bit(s) in
> question are also off in the physical MSR, but that would imply that
> Xen always has implemented at least all of the workarounds any guest
> may know of. I'm not sure I have a good other idea, short of allowing
> all writes to succeed.
> Jan
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