Re: [Xen-devel] Xen virtual IOMMU high level design doc

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: Wednesday, August 31, 2016 8:03 PM
> >>> 3.5 Implementation consideration
> >>> Linux Intel IOMMU driver will fail to be loaded without 2th level
> >>> translation support even if interrupt remapping and 1th level
> >>> translation are available. This means it's needed to enable 2th level
> >>> translation first before other functions.
> >>
> >> Is there a reason for this? I.e. do they unconditionally need that
> >> functionality?
> >
> > Yes, Linux intel IOMMU driver unconditionally needs l2 translation.
> > Driver checks whether there is a valid sagaw(supported Adjusted Guest
> > Address Widths) during initializing IOMMU data struct and return error
> > if not.
> 
> How about my first question then?
> 
> Jan

VT-d spec doesn't define a capability bit for the 2nd level translation 
(for 1st level or intr remapping, there do have such capability bit to
report). So architecturally there is no way to tell guest that 2nd level 
translation capability is not available, so existing Linux behavior is.... 
just correct.

Thanks
Kevin
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