[vfio-users] Mediated device interface + nvidia

[Alex Williamson]

On Thu, 15 Dec 2016 21:01:19 +0000
Zir Blazer <zir_blazer at hotmail.com> wrote:

> > This guide still indicates support for 4th generation (aka
> > Haswell), but I don't know how accurate it is:
> >
> > https://github.com/01org/gvt-linux/wiki/GVTg_Setup_Guide  
> 
> Probabily a typo or oversight. Here is a quote straight from one of the Intel devs from less than a month ago on iGVT-g Mailing List:
> https://lists.01.org/pipermail/igvt-g/2016-November/001024.html
> 
> Q: Will Haswell ever be put back into the validation matrix and possibly considered for KVM support?
> A: Unfortunately, the answer is no. :(
> KVMGT supported platform starts from Broadwell (including Broadwell). We have no plan to add Haswell platform code into KVMGT because Broadwell GPU has big difference with Haswell's.


I had assumed Broadwell since that's where support for Universal
Pass-Thru (UPT) mode starts for direct assigned IGD, but the setup
guide got my hopes up.  Darn.


> > One of the advantages of the vfio mediated device interface is that API
> > exposed to the user, and thus QEMU, is identical to a directly assigned
> > device.  Therefore AFAIK, there are no QEMU changes necessary for
> > KVMGT.  
> As far that I recall, QEMU modifications were required because iGVT-g added a lot of new invokation parameters, but I checked the new KVMGT Setup Guide you linked, and it seems that they changed the procedure a bit.
> 
> As of Sep 2016, according to near the end of this file:
> https://01.org/igvt-g/blogs/wangbo85/2016/kvmgt-environment-setup-guide-using-gvt-g-installation-iso
> ...in order to use iGVT-g in a VM, you had to invoke QEMU using these custom parameters:
> 
> -vgt
> -vga vgt
> -vgt_high_gm_sz 384
> -vgt_fence_sz 4
> -vgt_low_gm_sz 128
> 
> 
> On the guide you listed, here:
> https://github.com/01org/gvt-linux/wiki/GVTg_Setup_Guide
> ...instead, you use some command line parameters to create a vGPU in the host, then invoke QEMU with -device vfio-pci as if you were doing Passthrough but with a sysfsdev parameter pointing to the vGPU:
> 
> -vga none
> -device isa-vga
> -device vfio-pci,sysfsdev=/sys/bus/pci/devices/0000:00:02.0/894f3983-1a36-42b3-b52c-1024aca216be
> 
> 
> I didn't followed what changes they did to get the iGVT-g support upstream, but previously QEMU also needed a few tweaks to work with it. I suppose that some logic that they used to do in their custom QEMU got moved into the Kernel and thus it may work without further modifications, as you said.


Prior to this summer Intel was on a very different path to enable KVMGT
through QEMU.  Earlier prototypes used a completely different
architecture from what we have now, so I'm not surprised that you can
find older guides with QEMU options that exist anymore.  Thanks,

Alex