Re: [PATCH vfio 11/11] vfio/virtio: Introduce a vfio driver over virtio devices

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Sep 21, 2023 at 01:41:39PM -0300, Jason Gunthorpe wrote:
> On Thu, Sep 21, 2023 at 10:16:04AM -0400, Michael S. Tsirkin wrote:
> > On Thu, Sep 21, 2023 at 11:11:25AM -0300, Jason Gunthorpe wrote:
> > > On Thu, Sep 21, 2023 at 09:16:21AM -0400, Michael S. Tsirkin wrote:
> > > 
> > > > > diff --git a/MAINTAINERS b/MAINTAINERS
> > > > > index bf0f54c24f81..5098418c8389 100644
> > > > > --- a/MAINTAINERS
> > > > > +++ b/MAINTAINERS
> > > > > @@ -22624,6 +22624,12 @@ L:	kvm@vger.kernel.org
> > > > >  S:	Maintained
> > > > >  F:	drivers/vfio/pci/mlx5/
> > > > >  
> > > > > +VFIO VIRTIO PCI DRIVER
> > > > > +M:	Yishai Hadas <yishaih@nvidia.com>
> > > > > +L:	kvm@vger.kernel.org
> > > > > +S:	Maintained
> > > > > +F:	drivers/vfio/pci/virtio
> > > > > +
> > > > >  VFIO PCI DEVICE SPECIFIC DRIVERS
> > > > >  R:	Jason Gunthorpe <jgg@nvidia.com>
> > > > >  R:	Yishai Hadas <yishaih@nvidia.com>
> > > > 
> > > > Tying two subsystems together like this is going to cause pain when
> > > > merging. God forbid there's something e.g. virtio net specific
> > > > (and there's going to be for sure) - now we are talking 3
> > > > subsystems.
> > > 
> > > Cross subsystem stuff is normal in the kernel.
> > 
> > Yea. But it's completely spurious here - virtio has its own way
> > to work with userspace which is vdpa and let's just use that.
> > Keeps things nice and contained.
> 
> vdpa is not vfio, I don't know how you can suggest vdpa is a
> replacement for a vfio driver. They are completely different
> things.
> Each side has its own strengths, and vfio especially is accelerating
> in its capability in way that vpda is not. eg if an iommufd conversion
> had been done by now for vdpa I might be more sympathetic.

Yea, I agree iommufd is a big problem with vdpa right now. Cindy was
sick and I didn't know and kept assuming she's working on this. I don't
think it's a huge amount of work though.  I'll take a look.
Is there anything else though? Do tell.

> Asking for
> someone else to do a huge amount of pointless work to improve vdpa
> just to level of this vfio driver already is at is ridiculous.
> 
> vdpa is great for certain kinds of HW, let it focus on that, don't try
> to paint it as an alternative to vfio. It isn't.
> 
> Jason

There are a bunch of things that I think are important for virtio
that are completely out of scope for vfio, such as migrating
cross-vendor. What is the huge amount of work am I asking to do?



-- 
MST