Re: Two opens about iommufd pasid + IOPF

[Jason Gunthorpe <jgg@nvidia.com>]

On Fri, Aug 16, 2024 at 07:50:05PM +0800, Yi Liu wrote:
> 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?

You should always pass the handle

Alternatively you could use the xa based encoding I showed earlier to
store either handles or naked domains in the xarray. But really it
seems just fine to have iommufd allocate handle memory

> 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/

I would really like to remove IOMMU_DEV_FEAT_IOPF...

Jason