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

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2012-10-16 at 08:55 +0100, Jan Beulich wrote:
> >>> On 16.10.12 at 09:19, Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:
> > On Tue, 2012-10-16 at 08:08 +0100, Jan Beulich wrote:
> >> >>> 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?
> > 
> > iomem= support was committed to xl in xen-unstable last week or the week
> > before. I think it already existed in xend.
> 
> I fail to spot anything like that in xend - the only use of
> domain_iomem_permission() is in server\pciif.py afaics.

You are right. I saw iomem in the grep output and neglected to look at
the path.

Ian.


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