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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 06.03.12 at 12:55, "Liu, Jinsong" <jinsong.liu@xxxxxxxxx> wrote:
> 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?

That would be an option, but again only if OSes don't make
assumptions on the number of banks for certain CPU models.

Jan


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