Re: [Qemu-devel] [PATCH RFC] qdev: add init order filter

[Peter Xu]

On Thu, Mar 09, 2017 at 01:28:09PM +0100, Paolo Bonzini wrote:
> 
> 
> On 09/03/2017 13:11, Marcel Apfelbaum wrote:
> > On 03/09/2017 01:13 PM, Paolo Bonzini wrote:
> >>
> >>
> >> On 09/03/2017 00:59, Michael S. Tsirkin wrote:
> >>> Allow forcing a specific order of initialization on
> >>> devices created with -device.
> >>> Helpful e.g. for built-in devices such as IOMMUs which must
> >>> exist before all other devices.
> >>>
> >>> Signed-off-by: Michael S. Tsirkin <address@hidden>
> >>> ---
> >>>
> >>> Looks like we have a ton of problems because devices
> >>> are initialized in a random order, while we
> >>> really want e.g. iommu to be initialized
> >>> earlier than devices.
> >>>
> >>> This will be helpful for other things, e.g.
> >>> real hardware often is initialized in a specific order,
> >>> creating built-in devices for the board often
> >>> has to happen in a specific order, etc.
> >>
> >> In the specific case of PCI bus_master_as there is a simple workaround
> >> by placing a dummy container (which lets us build the AddressSpace) and
> >> then adding the alias region at machine_done time.
> >>
> >> This is exactly how MemoryListener is supposed to work, so I would start
> >> from there.
> >>
> > 
> > Hi Paolo,
> > 
> > This will certainly solve virtio-pci ordering issue, but I am not sure
> > it solves the vfio-pci problem. Here is a link to Alex's explanation:
> > 
> > http://www.mail-archive.com/address@hidden/msg432365.html
> 
> Right, VFIO is more complicated (hence "in the specific case of PCI
> bus_master_as").  I answered in that thread.

If we keep allowing vfio-pci to use pci_device_iommu_address_space()
(IMHO that's exactly the right thing to do there, rather than using
bus_master_as), this patch should work for vfio-pci as well? Since
vfio_realize() will get a correct iommu_fn, and that looks to be
enough.

Thanks,

-- peterx