linux-kernel - RE: [PATCH v2 3/4] iommufd: Destroy vdevice on idevice destroy

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Message-ID: <BN9PR11MB5276DCB10B6B08811206C3A28C78A@BN9PR11MB5276.namprd11.prod.outlook.com>
Date: Tue, 24 Jun 2025 08:22:11 +0000
From: "Tian, Kevin" <kevin.tian@...el.com>
To: Xu Yilun <yilun.xu@...ux.intel.com>, "jgg@...dia.com" <jgg@...dia.com>,
	"jgg@...pe.ca" <jgg@...pe.ca>, "will@...nel.org" <will@...nel.org>,
	"aneesh.kumar@...nel.org" <aneesh.kumar@...nel.org>
CC: "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"joro@...tes.org" <joro@...tes.org>, "robin.murphy@....com"
	<robin.murphy@....com>, "shuah@...nel.org" <shuah@...nel.org>,
	"nicolinc@...dia.com" <nicolinc@...dia.com>, "aik@....com" <aik@....com>,
	"Williams, Dan J" <dan.j.williams@...el.com>, "baolu.lu@...ux.intel.com"
	<baolu.lu@...ux.intel.com>, "Xu, Yilun" <yilun.xu@...el.com>
Subject: RE: [PATCH v2 3/4] iommufd: Destroy vdevice on idevice destroy

> From: Xu Yilun <yilun.xu@...ux.intel.com>
> Sent: Monday, June 23, 2025 5:50 PM
> 
> +static void iommufd_device_remove_vdev(struct iommufd_device *idev)
> +{
> +	bool vdev_removing = false;
> +
> +	mutex_lock(&idev->igroup->lock);
> +	if (idev->vdev) {
> +		struct iommufd_vdevice *vdev;
> +
> +		vdev = iommufd_get_vdevice(idev->ictx, idev->vdev->obj.id);
> +		if (IS_ERR(vdev)) {
> +			/* vdev is removed from xarray, but is not
> destroyed/freed */
> +			vdev_removing = true;
> +			goto unlock;
> +		}
> +
> +		/* Should never happen */
> +		if (WARN_ON(vdev != idev->vdev)) {
> +			idev->vdev = NULL;
> +			iommufd_put_object(idev->ictx, &vdev->obj);
> +			goto unlock;
> +		}
> +
> +		/*
> +		 * vdev cannot be destroyed after refcount_inc, safe to
> release

"vdev cannot be destroyed by userspace"

> +		 * idev->igroup->lock and use idev->vdev afterward.
> +		 */
> +		refcount_inc(&idev->vdev->obj.users);
> +		iommufd_put_object(idev->ictx, &idev->vdev->obj);

s/idev->vdev/vdev/

> @@ -124,18 +139,28 @@ int iommufd_vdevice_alloc_ioctl(struct
> iommufd_ucmd *ucmd)
>  		goto out_put_idev;
>  	}
> 
> +	mutex_lock(&idev->igroup->lock);
> +	if (idev->vdev) {
> +		rc = -EEXIST;
> +		goto out_unlock_igroup;
> +	}
> +
>  	vdev = iommufd_object_alloc(ucmd->ictx, vdev,
> IOMMUFD_OBJ_VDEVICE);
>  	if (IS_ERR(vdev)) {
>  		rc = PTR_ERR(vdev);
> -		goto out_put_idev;
> +		goto out_unlock_igroup;
>  	}
> 
> +	/* vdev can't outlive idev, vdev->idev is always valid, need no refcnt
> */
> +	vdev->idev = idev;
>  	vdev->ictx = ucmd->ictx;
>  	vdev->id = virt_id;
>  	vdev->dev = idev->dev;
>  	get_device(idev->dev);

this is not necessary now, as idevice already holds a reference to device
and now vdevice cannot outlive idevice.