[RFC PATCH kernel 0/5] powerpc/P9/vfio: Pass through NVIDIA Tesla V100

[Alex Williamson]

On Fri, 08 Jun 2018 07:54:02 +1000
Benjamin Herrenschmidt <benh at kernel.crashing.org> wrote:

> On Thu, 2018-06-07 at 11:04 -0600, Alex Williamson wrote:
> > 
> > Can we back up and discuss whether the IOMMU grouping of NVLink
> > connected devices makes sense?  AIUI we have a PCI view of these
> > devices and from that perspective they're isolated.  That's the view of
> > the device used to generate the grouping.  However, not visible to us,
> > these devices are interconnected via NVLink.  What isolation properties
> > does NVLink provide given that its entire purpose for existing seems to
> > be to provide a high performance link for p2p between devices?  
> 
> Not entire. On POWER chips, we also have an nvlink between the device
> and the CPU which is running significantly faster than PCIe.
> 
> But yes, there are cross-links and those should probably be accounted
> for in the grouping.

Then after we fix the grouping, can we just let the host driver manage
this coherent memory range and expose vGPUs to guests?  The use case of
assigning all 6 GPUs to one VM seems pretty limited.  (Might need to
convince NVIDIA to support more than a single vGPU per VM though)
Thanks,

Alex