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

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

      /* 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 ;).


Julien Grall

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