Re: [Xen-devel] [RFC PATCH 2/3] arch, arm32: add the XEN_DOMCTL_memory_mapping hypercall

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 03/03/14 19:56, Dario Faggioli wrote:
> On dom, 2014-03-02 at 17:56 +0800, Julien Grall wrote:
> > On 02/03/14 08:49, Arianna Avanzini wrote:
> > > +
> > > +        ret = -EPERM;
> > > +       /*
> > > +        * NOTE: dom0 seems to have empty iomem_caps but to be however able to
> > > +        *       access I/O memory ranges. The following check takes for granted
> > > +        *       that any iomem range can be mapped to a domU if the current
> > > +        *       domain is dom0.
> > > +        */
> > > +        if ( current->domain->domain_id != 0 &&
> > > +             !iomem_access_permitted(current->domain, mfn, mfn + nr_mfns - 1) )
> > > +            return ret;
> > This check can be removed by adding in construct_dom0
> > (arch/arm/domain_build.c) something like that:
> >     /* DOM0 is permitted full I/O capabilities */
> >     rc = iomem_permit_access(d, 0UL, ~OUL);
> Right. FTR, xen/arch/x86/domain_build.c, has this (also in
> construct_dom0):
>
>      /* DOM0 is permitted full I/O capabilities. */
>      rc |= ioports_permit_access(dom0, 0, 0xFFFF);
>      rc |= iomem_permit_access(dom0, 0UL, ~0UL);
>      rc |= irqs_permit_access(dom0, 1, nr_irqs_gsi - 1);
>
> Do you want a patch to that/similar effect?
Yes. Maybe a bit more smarter than permitting full I/0 caps for dom0.

> > I'm wondering if we can even restrict dom0 I/0 access by only permit
> > access on devices passthrough to it. Because dom0 should not be allowed
> > to map I/O ranges which belong to device used by Xen e.g : GIC, RAM,...
> So, this is probably me messing up with the terminology, but what
> 'devices passthrough to it [dom0]' would mean, for example in cases
> where we don't have an IOMMU (like cubie* boards), and hence where
> proper passtrhogh will never be, I think, supported? Or do we plan to
> have it working there too?
My term seems to be wrong for dom0 :).

On ARM, some device is used by Xen and therefore not exposed to dom0. By 
passthrough to dom0 I meant every device that are given to dom0, no 
matter if the platform has an IOMMU.
I think DOM0 should only be able to map theses devices to a guest. It 
seems stupid to allow dom0 mapping RAM or the UART used by Xen.
--
Julien Grall

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