Re: [RFC PATCH 3/4] iommu: Preallocate iommu group when probing devices

[Lu Baolu]

Hi Joerg,

On 1/17/20 6:21 PM, Joerg Roedel wrote:
> On Wed, Jan 01, 2020 at 01:26:47PM +0800, Lu Baolu wrote:
> > This splits iommu group allocation from adding devices. This makes
> > it possible to determine the default domain type for each group as
> > all devices belonging to the group have been determined.
>
> I think its better to keep group allocation as it is and just defer
> default domain allocation after each device is in its group. But take

I tried defering default domain allocation, but it seems not possible.

The call path of adding devices into their groups:

iommu_probe_device
-> ops->add_device(dev)
   -> (iommu vendor driver) iommu_group_get_for_dev(dev)

After doing this, the vendor driver will get the default domain and
apply dma_ops according to the domain type. If we defer the domain
allocation, they will get a NULL default domain and cause panic in
the vendor driver.

Any suggestions?

Best regards,
baolu

> care about the device hotplug path which might add new devices to groups
> which already have a default domain, or add new groups that might need a
> default domain too.