Re: [PATCH 3/4] KVM: PPC: Add support for IOMMU in-kernel handling

From: Benjamin Herrenschmidt
Date: Tue Jun 18 2013 - 00:39:40 EST

On Mon, 2013-06-17 at 20:32 -0600, Alex Williamson wrote:

> Right, we don't want to create dependencies across modules. I don't
> have a vision for how this should work. This is effectively a complete
> side-band to vfio, so we're really just dealing in the iommu group
> space. Maybe there needs to be some kind of registration of ownership
> for the group using some kind of token. It would need to include some
> kind of notification when that ownership ends. That might also be a
> convenient tag to toggle driver probing off for devices in the group.
> Other ideas? Thanks,

All of that smells nasty like it will need a pile of bloody
infrastructure.... which makes me think it's too complicated and not the
right approach.

How does access control work today on x86/VFIO ? Can you give me a bit
more details ? I didn't get a good grasp in your previous email....

>From the look of it, the VFIO file descriptor is what has the "access
control" to the underlying iommu, is this right ? So we somewhat need to
transfer (or copy) that ownership from the VFIO fd to the KVM VM.

I don't see a way to do that without some cross-layering here...

Rusty, are you aware of some kernel mechanism we can use for that ?


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