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Re: [Xen-devel] [PATCH 2/2] x86/vMCE: save/restore MCA capabilities

Jan Beulich wrote:
>>>> On 06.03.12 at 10:28, "Liu, Jinsong" <jinsong.liu@xxxxxxxxx> wrote:
>> Jan Beulich wrote:
>>> But we're getting all the farther away from the actual question: Do
>>> we need to provide for saving/restoring of any of the _CTL
>>> registers? 
>> Per Tony's elaboration about _CTL h/w meaning, I thought they are
>> model specific mainly used for debug purpose and os defaultly set
>> all 1's to them (if any misunderstanding please point out to me).
>> So how about unbind _CTL with host (say, pure software emulated msr,
>> not involve h_mcg_ctl/h_mci_ctrl[bank])? If so we don't need
>> save/restore _CTL. After all they are model specific, and emulated
>> as all 1's to guest seems reasonable.
> If the guest OS considers a particular CPU model to require an
> adjustment to any of these, any such adjustment would be lost over
> migration. I'm simply uncertain whether all OSes will tolerate that
> (in which case ignoring the writes in the first place would probably
> be better).

I'm unsure its risk but if concern OSes tolerance, it would better avoid such 
inconsistent case.
An update approach is, pure s/w emulated _CTL + save/restore, which would get 
rid of h/w heterogeneity and keep consistent when migrate.
Does it make sense?

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