Re: [Xen-devel] Xen-4.4-rc2 - Some Nested Virt testing

["Zhang, Yang Z" <yang.z.zhang@xxxxxxxxx>]

Tim Deegan wrote on 2014-01-27:
> B0;278;0cAt 08:29 +0000 on 26 Jan (1390721344), Zhang, Yang Z wrote:
>> George Dunlap wrote on 2014-01-25:
>>> On Tue, Jan 21, 2014 at 6:12 PM, Andrew Cooper
>>> <andrew.cooper3@xxxxxxxxxx> wrote:
>>>> Hello,
>>>> 
>>>> I have been giving nested virt a try, and have my first bug to report.
>>>> This is still ongoing, and is by no means complete yet.
>>>> 
>>>> Setup:
>>>> Each reference to XenServer is a trunk XenServer based on 4.4-rc2
>>>> 
>>>> Single Intel Haswell SDP (Grantley platform):
>>>> Native hypervisor: XenServer
>>>> 
>>>> Two L1 guests:
>>>>   XenServer (running with EPT)
>>>>   XenServer (running with shadow)
>>>> When attempting to create an L2 EPT HVM domain under an L1 shadow
>>>> domain, the L1 shadow domain is killed with:
>>> 
>>> Is EPT-on-shadow actually meant to work?  I wouldn't be surprised
>>> if the L2 HAP stuff assumed that L1 was HAP as well.
>>> 
>>> In which case, if an L1 guest is started in shadow mode, then EPT
>>> should not be advertised.
>> 
>> AFAK, EPT-on-shadow is not supported. Shadow-on-shadow is buggy
>> (Actually, I never tried it successfully from the first day I start
>> working on nested stuff).
> 
> Fair enough.  That needs to be documented, and those modes (which I
> guess means nested-on-shadow in general) need to be disabled in the
> hypervisor, with a sensible error message.
> 

Yes, I am working on writing the wiki page.

>> Shadow-on-EPT and EPT-on-EPT are working in my box. But I
>> recommended using EPT on EPT if possible. Because it is really a
>> pain to run L2 guest on shadow on shadow mode due to the poor performance.
> 
> Yeah, I think it's generally accepted that having shadow pagetables
> anywhere in that stack is going to hurt.  Sadly, there's no way for
> the L0 admin to stop the L1 hypervisor from using shadow pagetables,
> so shadow-on-EPT ought to at least work correctly, even if performance sucks.
> 
> Tim.


Best regards,
Yang



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