RE: [Xen-ia64-devel] Re: PMT table for XEN/IA64 (was: RE:Transparentparavirtualization vs. xen paravirtualization)

["Dong, Eddie" <eddie.dong@xxxxxxxxx>]

> 
> However, I agree with Matt that a PMT for other domains
> (domU) is a bad idea as it creates many problems for migration,
> save/restore, ballooning, and adding new domains to an already
> loaded system. Further, the grant table abstraction is the primary
> mechanism for page sharing for domU in Xen (on Xen/x86).
> I think if domU has any knowledge of actual machine addresses,
> the Xen team would consider this a bug that should be fixed.
> 
Dan:
        I think you get right reverse solution, without PMT in domU is a
nightmare for migration, balloning and etc.. We (Matt, Kevin and me)
believe PMT for domU is a must, because domU don't want to know where
the physical page is located, so gpn will always be from 0 for example
while mfn may start from any address, this is what PMT does to translate
from gpn to mfn. Today's dom0 is assume gpn=mfn so no PMT table yet,
that is what we are discussing to let dom0 have PMT same with domU.
        I guess you are probably assuming the PMT is a Xenlinux stuff,
actually PMT is a HV data structure even in Xen/X86 and Xen/IA64-VTi. HV
need to use PMT to insert machine side TLB for example, and sharing HV
PMT to paravirtualized guest should be done so that VBD and VNIF can
refer to. With PMT in dom0, we are just stepping toward close to Xen/X86
and reduce various maintaince effort and deviation.

Thx,eddie

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