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

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On Thu, Sep 21, 2023 at 04:51:15PM -0300, Jason Gunthorpe wrote:
> On Thu, Sep 21, 2023 at 03:17:25PM -0400, Michael S. Tsirkin wrote:
> > On Thu, Sep 21, 2023 at 03:39:26PM -0300, Jason Gunthorpe wrote:
> > > > What is the huge amount of work am I asking to do?
> > > 
> > > You are asking us to invest in the complexity of VDPA through out
> > > (keep it working, keep it secure, invest time in deploying and
> > > debugging in the field)
> > 
> > I'm asking you to do nothing of the kind - I am saying that this code
> > will have to be duplicated in vdpa,
> Why would that be needed?

For the same reason it was developed in the 1st place - presumably
because it adds efficient legacy guest support with the right card?
I get it, you specifically don't need VDPA functionality, but I don't
see why is this universal, or common.

> > and so I am asking what exactly is missing to just keep it all
> > there.
> VFIO. Seriously, we don't want unnecessary mediation in this path at
> all.

But which mediation is necessary is exactly up to the specific use-case.
I have no idea why would you want all of VFIO to e.g. pass access to
random config registers to the guest when it's a virtio device and the
config registers are all nicely listed in the spec. I know nvidia
hardware is so great, it has super robust cards with less security holes
than the vdpa driver, but I very much doubt this is universal for all
virtio offload cards.

> > note I didn't ask you to add iommufd to vdpa though that would be
> > nice ;)
> I did once send someone to look.. It didn't succeed :(
> Jason

Pity. Maybe there's some big difficulty blocking this? I'd like to know.


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