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

[Taiidan at gmx.com]

On 02/09/2017 07:23 PM, Alex Williamson wrote:

> 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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If the OP wants hardware reccs I like AMD's c32/g34 opteron's on a 
coreboot motherboard, they are a great option for a cheap *proper* iommu 
supporting virtualization setup ($20 per 16 cores).
On my no-blobs coreboot kgpe-d16 system every device gets its own iommu 
group.

Before that I bought two different computers that "supported" IOMMU and 
wasted too much money, even a lot of new intel "server" motherboards 
don't properly implement it for one reason or another so it is a good 
idea to go with a mobo/system that supports free firmware so that 
problems are fixable.
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