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

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On Thu, Sep 21, 2023 at 03:39:26PM -0300, Jason Gunthorpe wrote:
> On Thu, Sep 21, 2023 at 12:53:04PM -0400, Michael S. Tsirkin wrote:
> > > 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.
> Confidential compute will never work with VDPA's approach.

I don't see how what this patchset is doing is different
wrt to Confidential compute - you trap IO accesses and emulate.
Care to elaborate?

> > 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. 
> VFIO supports migration, if you want to have cross-vendor migration
> then make a standard that describes the VFIO migration data format for
> virtio devices.

This has nothing to do with data formats - you need two devices to
behave identically. Which is what VDPA is about really.

> > 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)
> When it doesn't provide *ANY* value to the solution.

There's no "the solution" - this sounds like a vendor only caring about
solutions that involve that vendor's hardware exclusively, a little.

> The starting point is a completely working vfio PCI function and the
> end goal is to put that function into a VM. That is VFIO, not VDPA.
> VPDA is fine for what it does, but it is not a reasonable replacement
> for VFIO.
> Jason

VDPA basically should be a kind of "VFIO for virtio".


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