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





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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