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 16:25 +0000, Eric Trudeau 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.
> > 
> 
> Our implementation does not require Dom0 access permission in order
> for it to grant access permission to a DomU.  I suppose it wouldn't hurt
> for iomem_permit_access because we allow iomem regions to be mapped
> into multiple domains; however, I think the irqs_permit_access call keeps
> multiple domains from "owning" the same IRQ.  I might be wrong about that.
> 
As far as I understood it, it is not required here either. And in fact,
such permission is not there, and things works for Arianna too.

However, it seemed a sane check to have in place (e.g., the x86
implementation does check for that), that's why she's trying to
introduce it properly. :-)

After all, as far as I remember, you do have something like this:

    if ( current->domain->domain_id != 0 )
        break;

don't you?

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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