Re: [Xen-devel] Sharing MMIO page with DomU on a system with no IOMMU

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 15.10.12 at 18:50, Martin Roth <gaumless@xxxxxxxxx> wrote:
> I'm trying to share an MMIO page from Dom0 running linux with a DomU 
> running an RTOS so that I can access the GPIO registers directly. The 
> system I need to get this working on does not have an IOMMU. I'm aware 
> of the security issues of sharing this area, but don't believe it's an 
> issue in this case.  I've got a Linux module set up and can share memory 
> between the two domains using the grant table, but I haven't been able 
> to get this to work for the MMIO page.
> 
> Can anyone give me a pointer on how I should go about doing this?  I 
> need the area to actually be shared between both domains, not simply 
> owned by the RTOS.

Looks like you have to assign the PCI device providing the GPIOs
to the guest, as there doesn't currently appear to be a way to
allow guest access to individual MMIO pages (lacking the MMIO
counterpart to the iports= and irqs= domain config settings).

Ian, Ian - am I overlooking something?

And of course - sharing the MMIO page between Dom0 and guest
is a questionable intention in any case - you rather want it owned
by the DomU, and Dom0 then shouldn't access it at all. Otherwise,
how would you expect accesses to be coordinated?

Jan


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