[CentOS-virt] PCI Passthrough not working

George Dunlap dunlapg at umich.edu
Mon May 16 13:25:30 UTC 2016


On Mon, May 16, 2016 at 2:14 PM, Francis Greaves <francis at choughs.net> wrote:
>>On Mon, May 16, 2016 at 12:00 PM, Francis Greaves <francis at choughs.net> wrote:
>>> Dear George please find attached the three files as requested.
>>> I have used
>>>
>>> iommu=soft
>>>
>>> in the grub command line for the kernel in the domU as explained before.
>>> many thanks
>
>>The options are:
>>1. Figure out what the other device is and assign them both to the guest
>>2. Tell Xen that you don't mind the sharing.
>>
>>You should only do #2 if you're not using Xen for isolation -- i.e.,
>>if you trust the software in that VM not to attack dom0.
>>
>>I *think* you should be able to do #2 by adding 'rdm_policy=relaxed'
>>to your pci stanza; i.e., it should look like this:
>>
>>pci=['00:1a.0,rdm_policy=relaxed']
>
> Dear George
> That worked, do I still need to add this to the cfg file?
>
> usb=1
> usbdevice=['host:0529:0514']
>
> or how do I assign the device without the 'rdm_policy=relaxed' option as per option 1?

Sorry, I don't understand your question.

In the pci case, you're passing through an entire USB controller.  The
guest will get access to anything plugged into that controller as
though it were running on native.

In the second case, you're presenting an emulated controller, and then
having qemu pass commands through to the device.  This should also
work, but may be a bit slower.

But for 4.6 it's only available in HVM mode -- and the config file you
attached was set up to run in PV mode (if I remember correctly).

> Thanks so much for your speedy advice.

Responding right away means I can delete it and forget about it. ;-)

 -George


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