[vfio-users] Unable to run two VMs at the same time

[Alex Williamson]

On Thu, Feb 9, 2017 at 5:09 PM, David Reed <david.byui at gmail.com> wrote:

> I've successfully been able to get two VMs setup with GPU/USB pass-through
> and individually they both work, but I can't run both of them at the same
> time.  Virt-manager will complain that the other's PCI device (GPU) is
> already in use even though they don't share the same GPU.
>
> I suspect it is because both GPUs have the same IOMMU group that is being
> assigned to the vfio driver.  I was hoping there would be some way to make
> this work as they are both being controlled by vfio.
>

Sorry, this is working as expected for your hardware.  The PCIe root ports
do not guarantee upstream routing, allowing the possibility of non-IOMMU
translated peer-to-peer between downstream devices.  See here for further
info  http://vfio.blogspot.com/2014/08/iommu-groups-inside-and-out.html
 Hacks to bypass this isolation are not supported upstream.  You can find
information about processors supporting isolation on root ports here:
http://vfio.blogspot.com/2015/10/intel-processors-with-acs-support.html
(it's a bit dated but you can extrapolate from the trend).  Thanks,

Alex
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