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

["Liu, Jinsong" <jinsong.liu@xxxxxxxxx>]

Liu, Jinsong wrote:
> Jan Beulich wrote:
>>>>> 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.
>> 
> 
> Afict the only way SDM recommand to get bank number is via mcg_cap,
> so if OS assume bank number via cpu model it would either get same
> number as that via mcg_cap or get wrong number which is OS problem
> not Xen.   
> 
> Thanks,
> Jinsong
> 

Jan, any more concern about this thread (_CTL)?

And, as for vMCE live migration, it indeed exist some issues when migrate. 
Currently we are discussing internally, and will present approach/patches when 
available.

Thanks,
Jinsong


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel