Re: [Xen-devel] [v6][PATCH 2/2] xen:vtd: missing RMRR mapping while share EPT

["Chen, Tiejun" <tiejun.chen@xxxxxxxxx>]

On 2014/7/30 16:36, Jan Beulich wrote:
> > > > On 30.07.14 at 03:36, <tiejun.chen@xxxxxxxxx> wrote:
> > --- a/xen/drivers/passthrough/vtd/iommu.c
> > +++ b/xen/drivers/passthrough/vtd/iommu.c
> > @@ -1867,8 +1867,14 @@ static int rmrr_identity_mapping(struct domain *d,
> >
> >       while ( base_pfn < end_pfn )
> >       {
> > -        if ( intel_iommu_map_page(d, base_pfn, base_pfn,
> > -                                  IOMMUF_readable|IOMMUF_writable) )
> > +        if ( iommu_use_hap_pt(d) )
> > +        {
> > +            ASSERT(!iommu_passthrough || !is_hardware_domain(d));
> > +            if ( set_identity_p2m_entry(d, base_pfn) )
> > +                return -1;
> > +        }
> > +        else if ( intel_iommu_map_page(d, base_pfn, base_pfn,
> > +                                       IOMMUF_readable|IOMMUF_writable) )
> >               return -1;
> >           base_pfn++;
> >       }
> So I wonder how this plays together with
>
>      /* FIXME: Because USB RMRR conflicts with guest bios region,
>       * ignore USB RMRR temporarily.
>       */
>      seg = pdev->seg;
>      bus = pdev->bus;
>      if ( is_usb_device(seg, bus, pdev->devfn) )
>      {
>          ret = 0;
>          goto done;
>      }
>
> later in the same file (in intel_iommu_assign_device()). I.e. the
> improvement you claim won't be achieved for passed through USB
I think we can remove this chunk of codes since these two patches 
already check if they conflicts.
> devices afaict. One more aspect supporting my view that this
> needs fully addressing rather than any such partial solution.
If we're talking about fixing all RMRR issues completely, these patches 
should not be enough. But I think these patches shouldn't block that 
complete solution because they're just checking to make sure we can 
create those RMRR mapping if possible. I mean no matter if we address 
more on RMRR, we still need these two patches to double-check/create 
RMRR mapping in shared EPT case, even we will reserve those ranges in 
guest as some guys recommended previously.
Thanks
Tiejun

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