Re: [PATCH v10 08/18] iommufd/device: Replace device_list with device_array

[Nicolin Chen <nicolinc@nvidia.com>]

On Thu, Mar 20, 2025 at 06:47:34AM -0700, Yi Liu wrote:
> igroup->attach->device_list is used to track attached device of a group
> in the RID path. Such tracking is also needed in the PASID path in order
> to share path with the RID path.
> 
> While there is only one list_head in the iommufd_device. It cannot work
> if the device has been attached in both RID path and PASID path. To solve
> it, replacing the device_list with an xarray. The attached iommufd_device
> is stored in the entry indexed by the idev->obj.id.
> 
> Signed-off-by: Yi Liu <yi.l.liu@intel.com>

Reviewed-by: Nicolin Chen <nicolinc@nvidia.com>

Nit:

>  static int iommufd_hwpt_attach_device(struct iommufd_hw_pagetable *hwpt,
> @@ -625,20 +634,27 @@ int iommufd_hw_pagetable_attach(struct iommufd_hw_pagetable *hwpt,
>  			rc = -ENOMEM;
>  			goto err_unlock;
>  		}
> -		INIT_LIST_HEAD(&attach->device_list);
> +		xa_init(&attach->device_array);
>  	}
>  
>  	old_hwpt = attach->hwpt;
>  
> +	rc = xa_insert(&igroup->attach->device_array, idev->obj.id, XA_ZERO_ENTRY,
> +		       GFP_KERNEL);
> +	if (rc) {
> +		WARN_ON(rc == -EBUSY && !old_hwpt);
> +		goto err_free_attach;
> +	}
> +
>  	if (old_hwpt && old_hwpt != hwpt) {
>  		rc = -EINVAL;
> -		goto err_free_attach;
> +		goto err_release_devid;
>  	}

Could we reject old_hwpt != hwpt (replace case) before xa_insert?