RE: [RFC][PATCH] 0/9 Populate-on-demand memory

["Han, Weidong" <weidong.han@intel.com>]

Tian, Kevin wrote:
>> From: Han, Weidong
>> Sent: Thursday, December 25, 2008 1:43 PM
>>>> 
>>>> At any rate, until we have that worked out, we should probably add
>>>> some "seatbelt" code to make sure that people don't use PoD for a
>>>> VT-d enabled domain.  I know absolutely nothing about the VT-d
>>>> code; could you either write a patch to do this check, or give me
>>>> an idea of the simplest thing to check?
>>> 
>>> Weidong works on VT-d and could give comments on exact point to
>>> check. 
>>> 
>> 
>> You can simply check "iommu_enabled" to know whether IOMMU
>> including VT-d and AMD IOMMU is used or not.
>> 
> 
> Weidong, does iommu_enabled indicate IOMMU h/w availability?
> Then you'll have this nice feature disabled on most new platform
> with IOMMU shipped. :-) Here a domain-based check is required,
> i.e. PoD is only appliable when target domain is not passthroughed
> with any device.
> 
> Thanks,
> Kevin

iommu_enabled will be set when IOMMU h/w is available and user sets "iommu=1" in grub to use it. Because device hotplug with VT-d is already supported, I think domain-based check is not enough, it's better to disable PoD when iommu_enabled is set. 

Regards,
Weidong