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

[Marcel Apfelbaum]

On 03/01/2017 11:59 AM, Peter Xu wrote:
> On Wed, Mar 01, 2017 at 11:29:47AM +0200, Marcel Apfelbaum wrote:
> > 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.
>
> That'll be great!
>
> > > 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.
>
> I think that won't be a big problem. E.g., I don't see big problem if
> we just create all these vIOMMUs along with machine init. Is there?

How would you assign them do devices?

The "normal" QEMU cmd line would look like I mentioned earlier:

-device iommu,id=iommu1 -device pcie-root,iommu=iommu1 \
-device pcie-root \
-device iommu,id=iommu2 -device pcie-root,iommu=iommu2 \

How do you propose to do it otherwise?

> IMHO we can just pick these vIOMMU "devices" out of the device list,
> and we can avoid doing that again in general device_init_func().
>
> > 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.
>
> IMHO it'll be okay we "pollute" vtd code for a short while. We can
> revert my patch (or any workarounds, like Jason's just posted one)

Can you please send me a link to Jason's patch?

If nobody else objects I am OK with it.

Thanks,
Marcel

> when we have device ordering support, and when we have a correct
> bus_master_as when device init.
>
> Thanks,
>
> -- peterx