Re: PCI Passthrough ARM Design : Draft1

[Ian Campbell <ian.campbell@citrix.com>]

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.

Ian.