Re: [PATCH 05/12] iommufd/hw_pagetable: Do not populate user-managed hw_pagetables

[Jason Gunthorpe <jgg@nvidia.com>]

On Thu, Mar 09, 2023 at 12:09:03AM -0800, Yi Liu wrote:
> From: Nicolin Chen <nicolinc@nvidia.com>
> 
> A user-managed hw_pagetable does not need to get populated, since it is
> managed by a guest OS. Move the iopt_table_add_domain and list_add_tail
> calls into a helper, where the hwpt pointer will be redirected to its
> hwpt->parent if it's available.
> 
> Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
> Signed-off-by: Yi Liu <yi.l.liu@intel.com>
> ---
>  drivers/iommu/iommufd/hw_pagetable.c | 20 ++++++++++++++++++--
>  1 file changed, 18 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iommu/iommufd/hw_pagetable.c b/drivers/iommu/iommufd/hw_pagetable.c
> index 16e92a1c150b..6e45ec0a66fa 100644
> --- a/drivers/iommu/iommufd/hw_pagetable.c
> +++ b/drivers/iommu/iommufd/hw_pagetable.c
> @@ -43,6 +43,23 @@ int iommufd_hw_pagetable_enforce_cc(struct iommufd_hw_pagetable *hwpt)
>  	return 0;
>  }
>  
> +static int iommufd_hw_pagetable_link_ioas(struct iommufd_hw_pagetable *hwpt)
> +{
> +	int rc;
> +
> +	if (hwpt->parent)

This should be:

   hwpt->domain->type != IOMMU_DOMAIN_UNMANAGED

Ie if we asked the driver to alloc a domain and it allocated an
UNMANAGED domain then it means IOMMUFD manages the mappings and it
should be populated from the IOAS.

Arguably drivers should EOPNOTSUPP if presented with a parent in this
situation, but still this code should be clear about the purpose.

> +		hwpt = hwpt->parent;

And we definately shouldn't touch the parent. That is already setup
and owned by someone else. Just return and don't do anything.

Jason