Re: [Qemu-devel] VFIO based vGPU(was Re: [Announcement] 2015-Q3 release of XenGT - a Mediated ...)

[Alex Williamson]

[cc +Neo @Nvidia]

Hi Jike,

On Mon, 2016-01-25 at 19:34 +0800, Jike Song wrote:
> On 01/20/2016 05:05 PM, Tian, Kevin wrote:
> > I would expect we can spell out next level tasks toward above
> > direction, upon which Alex can easily judge whether there are
> > some common VFIO framework changes that he can help :-)
> 
> Hi Alex,
> 
> Here is a draft task list after a short discussion w/ Kevin,
> would you please have a look?
> 
>       Bus Driver
> 
>               { in i915/vgt/xxx.c }
> 
>               - define a subset of vfio_pci interfaces
>               - selective pass-through (say aperture)
>               - trap MMIO: interface w/ QEMU

What's included in the subset?  Certainly the bus reset ioctls really
don't apply, but you'll need to support the full device interface,
right?  That includes the region info ioctl and access through the vfio
device file descriptor as well as the interrupt info and setup ioctls.

>       IOMMU
> 
>               { in a new vfio_xxx.c }
> 
>               - allocate: struct device & IOMMU group

It seems like the vgpu instance management would do this.

>               - map/unmap functions for vgpu
>               - rb-tree to maintain iova/hpa mappings

Yep, pretty much what type1 does now, but without mapping through the
IOMMU API.  Essentially just a database of the current userspace
mappings that can be accessed for page pinning and IOVA->HPA
translation.

>               - interacts with kvmgt.c
> 
> 
>       vgpu instance management
> 
>               { in i915 }
> 
>               - path, create/destroy
> 

Yes, and since you're creating and destroying the vgpu here, this is
where I'd expect a struct device to be created and added to an IOMMU
group.  The lifecycle management should really include links between
the vGPU and physical GPU, which would be much, much easier to do with
struct devices create here rather than at the point where we start
doing vfio "stuff".

Nvidia has also been looking at this and has some ideas how we might
standardize on some of the interfaces and create a vgpu framework to
help share code between vendors and hopefully make a more consistent
userspace interface for libvirt as well.  I'll let Neo provide some
details.  Thanks,

Alex