linux-kernel - Re: [PATCH 06/17] iommufd/hw_pagetable: Use domain_alloc

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Date:   Thu, 9 Feb 2023 12:59:58 -0500
From:   Matthew Rosato <mjrosato@...ux.ibm.com>
To:     Yi Liu <yi.l.liu@...el.com>, joro@...tes.org,
        alex.williamson@...hat.com, jgg@...dia.com, kevin.tian@...el.com,
        robin.murphy@....com
Cc:     cohuck@...hat.com, eric.auger@...hat.com, nicolinc@...dia.com,
        kvm@...r.kernel.org, chao.p.peng@...ux.intel.com,
        yi.y.sun@...ux.intel.com, peterx@...hat.com, jasowang@...hat.com,
        shameerali.kolothum.thodi@...wei.com, lulu@...hat.com,
        suravee.suthikulpanit@....com, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        baolu.lu@...ux.intel.com
Subject: Re: [PATCH 06/17] iommufd/hw_pagetable: Use domain_alloc_user op for
 domain allocation

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@...dia.com>
> Signed-off-by: Nicolin Chen <nicolinc@...dia.com>
> Signed-off-by: Yi Liu <yi.l.liu@...el.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