Re: [Qemu-devel] [PATCH v2] intel_iommu: check misordered init when realize

[Marcel Apfelbaum]

On 03/01/2017 11:18 AM, Peter Xu wrote:
> On Wed, Mar 01, 2017 at 09:03:47AM +0200, Marcel Apfelbaum wrote:
> > On 03/01/2017 06:14 AM, Jason Wang wrote:
>
> [...]
>
> > Hi Jason,
> >
> > I am not saying we don't need to create the IOMMU before some other device,
> > I just don't think that the command line order should matter to user.
> >
> > BTW, are you working on a way to limit the IOMMU scope to a specific set of 
> > devices?
> > If yes, this approach will also help you work.
>
> Marcel,
>
> Do you have any plan after 2.9 to re-arrange the init order thing a
> bit? In general, maybe we need an ordering support for devices.

I don;t know when I'll start it, but yes, I am thinking about
taking this project. We need the ordering in order to be able
to have less "built-in" devices.

> Besides that, I am thinking whether it would be wise that we just init
> the IOMMUs during machine init just like before, but keep the
> "-device" interface? After all, at least the root IOMMU device should
> be with root complex, and it feels a little strange we just split the
> init process apart (we delay the IOMMU init into device
> initializations).

Keeping the IOMMU creation as part of the Root Complex is problematic.
What happens if we want to limit the IOMMU scope to a subset of devices?
How will the command line look? Also we may want/need multiple iommu
devices per system. It will not happen tomorrow, but we don't want to loose
this possibility.

The device re-ordering is not 2.9 material of course, and we need your patch.
The only thing we can do better is to take out the "vfio-pci" in another header
file and and have it in a array of devices that should be checked
(in order to avoid polluting the IOMMU code with a not related device)

I can try and send a patch for it if you prefer.

Thanks,
Marcel

> Not sure whether above makes sense though. Thanks,
>
> -- peterx