linux-kernel - RE: [PATCH v4 07/17] iommufd: Add user-managed hw

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Date:   Tue, 26 Sep 2023 08:14:47 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     "Liu, Yi L" <yi.l.liu@...el.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "jgg@...dia.com" <jgg@...dia.com>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>
CC:     "cohuck@...hat.com" <cohuck@...hat.com>,
        "eric.auger@...hat.com" <eric.auger@...hat.com>,
        "nicolinc@...dia.com" <nicolinc@...dia.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "mjrosato@...ux.ibm.com" <mjrosato@...ux.ibm.com>,
        "chao.p.peng@...ux.intel.com" <chao.p.peng@...ux.intel.com>,
        "yi.y.sun@...ux.intel.com" <yi.y.sun@...ux.intel.com>,
        "peterx@...hat.com" <peterx@...hat.com>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        "shameerali.kolothum.thodi@...wei.com" 
        <shameerali.kolothum.thodi@...wei.com>,
        "lulu@...hat.com" <lulu@...hat.com>,
        "suravee.suthikulpanit@....com" <suravee.suthikulpanit@....com>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
        "Duan, Zhenzhong" <zhenzhong.duan@...el.com>,
        "Martins, Joao" <joao.m.martins@...cle.com>
Subject: RE: [PATCH v4 07/17] iommufd: Add user-managed hw_pagetable support

> From: Liu, Yi L <yi.l.liu@...el.com>
> 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().