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

To: "Liping Ke" <liping.ke@xxxxxxxxx>, "Yunhong Jiang" <yunhong.jiang@xxxxxxxxx>
Subject: Re: [Xen-devel] mce_wrmsr() and (at least) HVM guests
From: "Jan Beulich" <JBeulich@xxxxxxxxxx>
Date: Tue, 22 Dec 2009 13:02:35 +0000
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>>> "Jan Beulich" <JBeulich@xxxxxxxxxx> 01.12.09 12:19 >>>
>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.



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