Re: [Xen-devel] [PATCH] libxc: Expose the pdpe1gb cpuid flag to guest

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

Jan Beulich wrote on 2014-11-25:
>>>> On 25.11.14 at 02:47, <yang.z.zhang@xxxxxxxxx> wrote:
>> Tim Deegan wrote on 2014-11-19:
>>> At 01:29 +0000 on 19 Nov (1416356943), Zhang, Yang Z wrote:
>>>> Tim Deegan wrote on 2014-11-18:
>>>>> In this case, the guest is entitled to _expect_ pagefaults on 1GB
>>>>> mappings if CPUID claims they are not supported.  That sounds
>>>>> like an unlikely thing for the guest to be relying on, but Xen
>>>>> itself does something similar for the SHOPT_FAST_FAULT_PATH (and
>>>>> now also for IOMMU entries for the deferred caching attribute updates).
>>>> 
>>>> Indeed. How about adding the software check (as Andrew mentioned)
>>>> firstly and leave the hardware problem (Actually, I don't think we
>>>> can solve it currently).
>>> 
>>> I don't think we should change the software path unless we can
>>> change the hardware behaviour too.  It's better to be consistent,
>>> and it saves us some cycles in the pt walker.
>> 
>> So if we don't need to add the software check, does this mean
>> current patch is ok?
> 
> No - Tim having confirmed that shadow mode doesn't support 1Gb pages,
> the feature clearly must not be made visible for shadow mode guest.

Indeed. Liang, Can you add the shadow mode check in the next version?

> 
> Jan


Best regards,
Yang



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