Re: [Xen-devel] PCI Passthrough ARM Design : Draft1

[Manish Jaggi <mjaggi@xxxxxxxxxxxxxxxxxx>]

On Friday 12 June 2015 01:32 AM, Ian Campbell wrote:
> On Thu, 2015-06-11 at 14:38 -0700, Manish Jaggi wrote:
> > On Wednesday 10 June 2015 12:21 PM, Julien Grall wrote:
> > > Hi,
> > >
> > > On 10/06/2015 08:45, Ian Campbell wrote:
> > > > > 4. DomU access / assignment PCI device
> > > > > --------------------------------------
> > > > > When a device is attached to a domU, provision has to be made such that
> > > > > it can
> > > > > access the MMIO space of the device and xen is able to identify the
> > > > > mapping
> > > > > between guest bdf and system bdf. Two hypercalls are introduced
> > > > I don't think we want/need new hypercalls here, the same existing
> > > > hypercalls which are used on x86 should be suitable.
> > I think both the hypercalls are necessary
> > a) the mapping of guest bdf to actual sbdf is required as domU accesses
> > for GIC are trapped and not handled by pciback.
> > A device say 1:0:0.3 is assigned in domU at 0:0:0.3. This is the bestway
> > I could find that works.
> >
> > b) map_mmio call is issued just after the device is added on the pcu bus
> > (in case of domU)
> > The function register_xen_pci_notifier (drivers/xen/pci.c) is modified
> > such that notification is received in domU and dom0.
> In which please please add to the document a discussion of the current
> interfaces and why they are not suitable.
>
> > > Beware that the 1:1 mapping doesn't fit with the current guest memory
> > > layout which is pre-defined at Xen build time. So you would also have
> > > to make it dynamically or decide to use the same memory layout as the
> > > host.
> > If same layout as host used, would there be any issue?
> I'm not sure that a 1:1 mapping is any different to the host layout. But
> in any case, the host layout also doesn't match the guest layout, so it
> has the same issues.
There is a domctl on x86 DOMCTL_iomem_permission which looks doing the 
same thing as the map_mmio hypercall which I am proposing. I am not sure 
if it does a 1:1. Do you have more info on it?
> Ian.
>
>
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