Re: [Qemu-devel] [Xen-devel] [PATCH RFC V1 00/11] Xen PCI Passthrough

[Jan Kiszka <jan.kiszka@web.de>]

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On 2011-10-04 17:01, Anthony Liguori wrote:
> On 10/04/2011 09:58 AM, Avi Kivity wrote:
>> On 10/04/2011 04:51 PM, Anthony PERARD wrote:
>>> Hi all,
>>>
>>> This patch series introduce the PCI passthrough for Xen.
>>>
>>> First, we have HostPCIDevice that help to access one PCI device of
>>> the host.
>>>
>>> Then, there are several additions in the QEMU code. One is
>>> qemu_run_one_timer
>>> to run a specific timer. It is used by PCI passthrough to run a timer
>>> about
>>> power management. Another is pci_check_bar_overlap.
>>>
>>> There are also several change in pci_ids and pci_regs.
>>>
>>> Last part, but not least, the PCI passthrough device himself. Cut in
>>> 3 parts
>>> (or file), there is one to take care of the initialisation of a
>>> passthrough
>>> device. The second one handle everything about the config address
>>> space, there
>>> are specifics functions for every config register. The third one is
>>> to handle
>>> MSI.
>>>
>>> I'm still working on setting a PCI passthrough device through QMP
>>> from libxl
>>> (xen tool stack). It is just a call to device_add, with the driver
>>> parametter
>>> hostaddr="0000:00:1b.0".
>>>
>>> There is some minor things missing:
>>> - copyright header
>>> - PCI IO space multiplexer
>>>
>>>
>>
>> We also have pci passthrough in qemu-kvm (I think based on the same
>> Neocleus
>> code). Rather than having two pci assignment implementations, I think
>> we should
>> have just one, with the differences (programming the hypervisor)
>> abstracted at
>> that level.
> 
> I agree in principle but how close is qemu-kvm pci passthrough to a
> mergable state?  Would it make sense to merge the Xen code first and
> then abstract it?

What is missing to get qemu-kvm device assignment ready:
 - MSI/MSI-X refactoring in QEMU (specifically config notifiers, also
   relevant for virtio)
 - switch device assignment to generic MSI/MSI-X
 - get in-kernel irqchip support upstream
 - minor code cleanups

I was hoping to complete this for 1.0, but it looks unrealistic now.
Maybe I'll find the time for the MSI stuff at least.

From a first glance at these patches, I think there are already some
synergies in the host-pci access layer. And I bet the Xen bits could
also make use of our MSI/MSI-X code once it's generalized. But that will
be a bit work for them (based on my experience with qemu-kvm).

Jan


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