[libvirt-users] PCI passthrough error

[Jaap Winius]

Quoting Jaap Winius <jwinius at umrk.nl>:

> ... Anyway I guess now it's USB passthrough or bust. Or get
> a board with an IOMMU.

In case anyone is ever interested, I did eventually manage to solve  
this problem with a wrapper script, although not exactly the way David  
Wragg explains in his blog.

With Debian squeeze, the problem is that when using virt-manager to  
configure USB passthrough, it allows you to select a USB device based  
on its vendorID and productID combination, which happens to be exactly  
what I need. However, when passing the selected device on to the  
virtual machine, the kvm command it generates is only for the  
bus/device combination that the selected device is currently using.  
That, combined with the lack of any hot-plug support is what was  
preventing me from getting my system to work.

The solution for me was simply to bypass any methods using  
virt-manager or the virsh editor to define the devices for USB  
passthrough. Then, instead of using the wrapper script to modify any  
devices already defined, I use it to add all of the devices I need. It  
looks like this:

#!/bin/sh
exec /usr/bin/kvm `echo $* | sed 's/-vga std/-vga std -usbdevice  
host:auto:*.*:0c93:1772 -usbdevice host:auto:*.*:0c93:1771/'`

Incidentally, this script has to have the same name as the executable,  
which on Debian squeeze is /usr/bin/kvm. So, I called this script  
/usr/local/bin/kvm, and not /usr/local/bin/qemu-kvm, like in Wragg's  
blog.

Anyway, the above script allows me to start up the virtual machine  
with only one (or none) of the devices attached. Then the theory is  
that the Windows device driver loads some firmware into the device,  
which causes it to change its product ID from 1772 to 1771, as well as  
its device number. Crucially, my wrapper script doesn't care about  
this device number change and the new device is also passed through to  
the virtual machine. As far as I can tell, the Windows software  
continues to work as expected.

Cheers,

Jaap