From:   "Tian, Kevin" <kevin.tian@intel.com>
To:     "Liu, Yi L" <yi.l.liu@intel.com>,
        "alex.williamson@redhat.com" <alex.williamson@redhat.com>,
        "jgg@nvidia.com" <jgg@nvidia.com>
CC:     "cohuck@redhat.com" <cohuck@redhat.com>,
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        "nicolinc@nvidia.com" <nicolinc@nvidia.com>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "mjrosato@linux.ibm.com" <mjrosato@linux.ibm.com>,
        "chao.p.peng@linux.intel.com" <chao.p.peng@linux.intel.com>,
        "yi.y.sun@linux.intel.com" <yi.y.sun@linux.intel.com>,
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        <shameerali.kolothum.thodi@huawei.com>,
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        "intel-gvt-dev@lists.freedesktop.org" 
        <intel-gvt-dev@lists.freedesktop.org>,
        "intel-gfx@lists.freedesktop.org" <intel-gfx@lists.freedesktop.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
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Subject: RE: [PATCH v2 11/14] vfio: Make vfio_device_open() exclusive between
 group path and device cdev path
Thread-Topic: [PATCH v2 11/14] vfio: Make vfio_device_open() exclusive between
 group path and device cdev path
Thread-Index: AQHZOgpBum+2XsDSRkm84tYt2roRMa7DBLFg
Date:   Tue, 7 Feb 2023 06:24:54 +0000
Message-ID: <BN9PR11MB52764ED1F43F717E04B8E3588CDB9@BN9PR11MB5276.namprd11.prod.outlook.com>
References: <20230206090532.95598-1-yi.l.liu@intel.com>
 <20230206090532.95598-12-yi.l.liu@intel.com>
In-Reply-To: <20230206090532.95598-12-yi.l.liu@intel.com>
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> From: Liu, Yi L <yi.l.liu@intel.com>
> Sent: Monday, February 6, 2023 5:05 PM
>=20
>  struct vfio_device_file *
> -vfio_allocate_device_file(struct vfio_device *device)
> +vfio_allocate_device_file(struct vfio_device *device, bool is_cdev_devic=
e)
>  {
>  	struct vfio_device_file *df;
>=20
> @@ -407,6 +407,7 @@ vfio_allocate_device_file(struct vfio_device *device)
>  		return ERR_PTR(-ENOMEM);
>=20
>  	df->device =3D device;
> +	df->is_cdev_device =3D is_cdev_device;

You missed Alex's comment that the one caller can open code the
assignment instead of introducing an unmemorable Boolean arg here.

>=20
> +	/*
> +	 * Device cdev path cannot support multiple device open since
> +	 * it doesn't have a secure way for it. So a second device
> +	 * open attempt should be failed if the caller is from a cdev
> +	 * path or the device has already been opened by a cdev path.
> +	 */
> +	if (device->open_count !=3D 0 &&
> +	    (df->is_cdev_device || device->single_open))
> +		return -EINVAL;
> +

If we are gonna handle the exclusive open via dma ownership, then
here we don't need a new single_open flag inside vfio_device since
only one interface (cdev or group) could be used to open this device.

Just preventing multi-open in cdev is sufficient here.