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 09:44
> 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 10:31, <Paul.Durrant@xxxxxxxxxx> wrote:
> >> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> >> Sent: 07 September 2018 12:11
> >>
> >> >>> On 23.08.18 at 11:47, <paul.durrant@xxxxxxxxxx> wrote:
> >> > This patch adds a new method to the VT-d IOMMU implementation to
> find
> >> the
> >> > MFN currently mapped by the specified BFN along with a wrapper
> function
> >> in
> >> > generic IOMMU code to call the implementation if it exists.
> >>
> >> For this to go in, I think the AMD side of it wants to also be implemented.
> >>
> >> > --- a/xen/drivers/passthrough/iommu.c
> >> > +++ b/xen/drivers/passthrough/iommu.c
> >> > @@ -305,6 +305,17 @@ int iommu_unmap_page(struct domain *d,
> bfn_t
> >> bfn)
> >> >      return rc;
> >> >  }
> >> >
> >> > +int iommu_lookup_page(struct domain *d, bfn_t bfn, mfn_t *mfn,
> >> > +                      unsigned int *flags)
> >> > +{
> >> > +    const struct domain_iommu *hd = dom_iommu(d);
> >> > +
> >> > +    if ( !iommu_enabled || !hd->platform_ops )
> >> > +        return -EOPNOTSUPP;
> >> > +
> >> > +    return hd->platform_ops->lookup_page(d, bfn, mfn, flags);
> >> > +}
> >>
> >> Shouldn't this be restricted to PV guests? HVM ones aren't supposed
> >> to know about MFNs.
> >
> > Agreed, but I think this is the wrong level to be applying such a check:
> > iommu_map_page() is supplied an MFN regardless of whether the domain
> is PV or
> > HVM, so I think it is reasonable for a lookup function to work in terms of
> > MFNs.
> 
> I don't mind much where the check sits, but ASSERT(!is_hvm_domain()),
> if placed here, should not trigger.
> 

It will though. I'm going to need to use this function for HVM guests after 
having done a GFN lookup.

  Paul

> Jan
> 


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