Re: [PATCH rfcv2 03/20] HostIOMMUDevice: Introduce realize_late callback

["Cédric Le Goater" <clg@redhat.com>]

On 4/7/25 13:19, Cédric Le Goater wrote:
> On 2/19/25 09:22, Zhenzhong Duan wrote:
>> Currently we have realize() callback which is called before attachment.
>> But there are still some elements e.g., hwpt_id is not ready before
>> attachment. So we need a realize_late() callback to further initialize
>> them.
> 
> The relation between objects HostIOMMUDevice and VFIOIOMMU is starting
> to look too complex for me.
> 
> I think it makes sense to realize HostIOMMUDevice after the device
> is attached. Can't we move :
> 
>          hiod = HOST_IOMMU_DEVICE(object_new(ops->hiod_typename));
>          vbasedev->hiod = hiod;
> 
> under ->attach_device() and also the call :
> 
>      if (!vfio_device_hiod_realize(vbasedev, errp)) {
> 
> later in the ->attach_device() patch ?
> 
> hiod_legacy_vfio_realize() doesn't do much. We might need to rework
> hiod_iommufd_vfio_realize() which queries the iommufd hw caps, later
> used by intel-iommu.

The only dependency I see on the IOMMUFD HostIOMMUDevice when attaching
the device to the container is in iommufd_cdev_autodomains_get(). The
flags for IOMMU_HWPT_ALLOC depends on the HW capability of the IOMMFD
backend and we rely on hiod_iommufd_vfio_realize() to have done the
query on the iommufd kernel device before.

Since this is not a hot path, I don't think it is a problem to add
a redundant call to iommufd_backend_get_device_info() in
iommufd_cdev_autodomains_get() and avoid the IOMMUFD HostIOMMUDevice
dependency. With that we can move the HostIOMMUDevice creation and
realize sequence at the end of the device attach sequence.

I think this makes the code cleaner when it comes to using the
vbasedev->hiod pointer too.

> Anyway, it is good time to cleanup our interfaces before adding more.

On that topic, I think

    iommufd_cdev_attach_ioas_hwpt
    iommufd_cdev_detach_ioas_hwpt

belong to IOMMUFD backend.


Thanks,

C.