RE: [PATCH v4 07/17] iommufd: Add user-managed hw_pagetable support

[Tian, Kevin]

> From: Liu, Yi L <yi.l.liu@xxxxxxxxx>
> Sent: Thursday, September 21, 2023 3:51 PM
> 
> +static void iommufd_user_managed_hwpt_abort(struct iommufd_object
> *obj)
> +{
> +	struct iommufd_hw_pagetable *hwpt =
> +		container_of(obj, struct iommufd_hw_pagetable, obj);
> +
> +	/* The parent->mutex must be held until finalize is called. */
> +	lockdep_assert_held(&hwpt->parent->mutex);
> +
> +	iommufd_hw_pagetable_destroy(obj);
> +}

Can you elaborate what exactly is protected by parent->mutex?

My gut-feeling that the child just grabs a refcnt on the parent
object. It doesn't change any other data of the parent.

> 
> +/**
> + * iommufd_user_managed_hwpt_alloc() - Get a user-managed
> hw_pagetable
> + * @ictx: iommufd context
> + * @pt_obj: Parent object to an HWPT to associate the domain with
> + * @idev: Device to get an iommu_domain for
> + * @flags: Flags from userspace
> + * @hwpt_type: Requested type of hw_pagetable
> + * @user_data: user_data pointer
> + * @dummy: never used
> + *
> + * Allocate a new iommu_domain (must be IOMMU_DOMAIN_NESTED) and
> return it as
> + * a user-managed hw_pagetable.

Add some text to highlight the requirement being a parent, e.g. not
an auto domain, must be capable of being a parent, etc.

> +	case IOMMUFD_OBJ_HW_PAGETABLE:
> +		parent = container_of(pt_obj, struct iommufd_hw_pagetable,
> obj);
> +		/* No user-managed HWPT on top of an user-managed one
> */
> +		if (parent->user_managed) {
> +			rc = -EINVAL;
> +			goto out_put_pt;
> +		}

move to alloc_fn().