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

[Julien Grall <julien.grall@xxxxxxxxxx>]

Hi Dario,

On 03/03/14 23:33, Dario Faggioli wrote:
> 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" ? :-)
No :).

> > > 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 think the best place to permit access is in map_device 
(xen/arch/arm/domain_build.c).
This function is called for every devices used  by dom0 to map I/O mem 
and IRQ.
> 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. :-)
Either the ML or #xenarm channel on Freenode are the best to ask question.
Arianna, I advice you to join the IRC channel if it's not already the 
case ;).
Cheers,

--
Julien Grall

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