Re: [Xen-devel] [PATCH v6 08/14] vtd: add lookup_page method to iommu_ops

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: 12 September 2018 10:13
> To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
> Cc: George Dunlap <George.Dunlap@xxxxxxxxxx>; Kevin Tian
> <kevin.tian@xxxxxxxxx>; xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
> Subject: RE: [PATCH v6 08/14] vtd: add lookup_page method to iommu_ops
> 
> >>> On 12.09.18 at 11:05, <Paul.Durrant@xxxxxxxxxx> wrote:
> >> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> >> Sent: 12 September 2018 10:03
> >>
> >> A HVM guest using the PV IOMMU is quite fine, but it shouldn't talk to
> >> it in terms of MFNs.
> >>
> >
> > Well, it has to talk MFNs at some level, surely? The output of the IOMMU is
> > not subject to EPT/NPT, right?
> 
> Yes to the second question, but no to the first: The GFN -> MFN translation
> should still be done inside Xen in the HVM case, imo (in the course of
> manufacturing the PTE).

Indeed. This function is very much internal to Xen (it's simply an abstraction 
on top of a vendor implementation), so why should it not work in terms of MFNs? 
There's no hypercall that allows this to be blindly called by an HVM guest.

  Paul

> 
> Jan
> 


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