Re: [PATCH 06/17] iommufd/hw_pagetable: Use domain_alloc_user op for domain allocation

[Matthew Rosato <mjrosato@linux.ibm.com>]

On 2/8/23 11:31 PM, Yi Liu wrote:
> This converts iommufd to use iommu_domain_alloc_user() for iommu_domain
> creation.
> 
> Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
> Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
> Signed-off-by: Yi Liu <yi.l.liu@intel.com>
> ---
>  drivers/iommu/iommufd/hw_pagetable.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/iommufd/hw_pagetable.c b/drivers/iommu/iommufd/hw_pagetable.c
> index 43d473989a06..08d963ee38c7 100644
> --- a/drivers/iommu/iommufd/hw_pagetable.c
> +++ b/drivers/iommu/iommufd/hw_pagetable.c
> @@ -30,6 +30,7 @@ struct iommufd_hw_pagetable *
>  iommufd_hw_pagetable_alloc(struct iommufd_ctx *ictx, struct iommufd_ioas *ioas,
>  			   struct device *dev)
>  {
> +	const struct iommu_ops *ops;
>  	struct iommufd_hw_pagetable *hwpt;
>  	int rc;
>  
> @@ -37,7 +38,13 @@ iommufd_hw_pagetable_alloc(struct iommufd_ctx *ictx, struct iommufd_ioas *ioas,
>  	if (IS_ERR(hwpt))
>  		return hwpt;
>  
> -	hwpt->domain = iommu_domain_alloc(dev->bus);
> +	ops = dev_iommu_ops(dev);
> +	if (!ops || !ops->domain_alloc_user) {
> +		rc = -EOPNOTSUPP;
> +		goto out_abort;
> +	}

Hi Yi,

This seems to break the iommufd vfio container support for any iommu that hasn't implemented domain_alloc_user yet.

I noticed it using vfio-pci on s390 with

CONFIG_IOMMUFD=m
CONFIG_IOMMUFD_VFIO_CONTAINER=y
CONFIG_VFIO_GROUP=y

Not sure if the intent is to make domain_alloc_user a hard requirement for using iommufd (if so then the commit description really should highlight that).  Otherwise, conditionally calling iommu_domain_alloc(dev->bus) when !ops->domain_alloc_user (instead of returning -EOPNOTSUPP) seems to restore the prior functionality for me.

Thanks,
Matt