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

[Dario Faggioli <dario.faggioli@citrix.com>]

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On lun, 2014-03-03 at 23:20 +0800, Julien Grall wrote:
> On 03/03/14 19:56, Dario Faggioli wrote:

> > 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.
> 
EhEh... do you mean to say that x86 is "not smart" ? :-)

> > 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.
> 
Ok, now I got it.

> 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.
> 
I see, and it does make sense.

Of course, I really don't know what these devices are and what the best
approach would be to hide/revoke permissions to their iomem/irqs (e.g.,
allow everything and then revoke some, allow selectively in the first
place, etc.).

I'm quite sure Arianna is keen on helping with this, but it better be,
if possible, someone of you ARM folks suggesting her what, where and
how. :-)

Thanks and Regards,
Dario

-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)


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