Two opens about iommufd pasid + IOPF

[Yi Liu <yi.l.liu@intel.com>]

Hi Kevin, Baolu, Jason,

I've got two opens when rebasing iommufd pasid series on top of 6.11.
Would like to hear about your ideas. :)

1) How to retrieve attached domain for pasid in the iommu core. This is
    needed when adding domain replacement for pasid. In the before, it can
    be done by searching the group->pasid_array[1]. However, the
    group->pasid_array stores iommu_attach_handle after the iopf patch [2].
    IIUC, iommu_attach_handle is passed only when the domain is
    iopf-capable. So, if the old domain does not support iopf, then it's not
    able to get this old domain from the group->pasid_array when trying to
    do domain replacement. :(
    Not sure if any side-effect if I always pass an iommu_attach_handle even
    if the hwpt/domain is not iopf-capable. @Baolu?

2) Should I enable/disable IOPF when attaching/detaching pasid to/from
    domains just like patch [3] does?

[1] 
https://lore.kernel.org/linux-iommu/20240628090557.50898-2-yi.l.liu@intel.com/
[2] 
https://lore.kernel.org/linux-iommu/20240702063444.105814-2-baolu.lu@linux.intel.com/
[3] 
https://lore.kernel.org/linux-iommu/20240702063444.105814-8-baolu.lu@linux.intel.com/

-- 
Regards,
Yi Liu