Re: [PATCH 09/14] iommufd: Add iommufd_device_replace()

[Baolu Lu <baolu.lu@linux.intel.com>]

On 2/25/23 8:27 AM, Jason Gunthorpe wrote:
> +/**
> + * iommufd_device_attach - Connect a device to an iommu_domain
> + * @idev: device to attach
> + * @pt_id: Input a IOMMUFD_OBJ_IOAS, or IOMMUFD_OBJ_HW_PAGETABLE
> + *         Output the IOMMUFD_OBJ_HW_PAGETABLE ID

"Output the hwpt ID" only happens when the caller input an IOAS object
and an auto domain was selected or created for the device.

Do I understand it right?

> + *
> + * This connects the device to an iommu_domain, either automatically or manually
> + * selected. Once this completes the device could do DMA.
> + *
> + * The caller should return the resulting pt_id back to userspace.
> + * This function is undone by calling iommufd_device_detach().
> + */
> +int iommufd_device_attach(struct iommufd_device *idev, u32 *pt_id)
> +{
> +	int rc;
> +
> +	rc = iommufd_device_change_pt(idev, pt_id, &iommufd_device_do_attach);
> +	if (rc)
> +		return rc;
> +
> +	/*
> +	 * Pairs with iommufd_device_detach() - catches caller bugs attempting
> +	 * to destroy a device with an attachment.
> +	 */
> +	refcount_inc(&idev->obj.users);
> +	return 0;
>   }
>   EXPORT_SYMBOL_NS_GPL(iommufd_device_attach, IOMMUFD);
>   
> +/**
> + * iommufd_device_replace - Change the device's iommu_domain
> + * @idev: device to change
> + * @pt_id: Input a IOMMUFD_OBJ_IOAS, or IOMMUFD_OBJ_HW_PAGETABLE
> + *         Output the IOMMUFD_OBJ_HW_PAGETABLE ID

If my above understanding is correct, then replace will never output a
hwpt id as it only happens after a successful attach.

> + *
> + * This is the same as:
> + *   iommufd_device_detach();
> + *   iommufd_device_attach()
> + * If it fails then no change is made to the attachment. The iommu driver may
> + * implement this so there is no disruption in translation. This can only be
> + * called if iommufd_device_attach() has already succeeded.
> + */
> +int iommufd_device_replace(struct iommufd_device *idev, u32 *pt_id)
> +{
> +	return iommufd_device_change_pt(idev, pt_id,
> +					&iommufd_device_do_replace);
> +}
> +EXPORT_SYMBOL_NS_GPL(iommufd_device_replace, IOMMUFD);

Best regards,
baolu