linux-kernel - RE: [PATCH v2 11/14] vfio: Make vfio_device_open() exclusive between group path and device cdev path

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Date:   Tue, 7 Feb 2023 06:24:54 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     "Liu, Yi L" <yi.l.liu@...el.com>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "jgg@...dia.com" <jgg@...dia.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>,
        "intel-gvt-dev@...ts.freedesktop.org" 
        <intel-gvt-dev@...ts.freedesktop.org>,
        "intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>
Subject: RE: [PATCH v2 11/14] vfio: Make vfio_device_open() exclusive between
 group path and device cdev path

> From: Liu, Yi L <yi.l.liu@...el.com>
> Sent: Monday, February 6, 2023 5:05 PM
> 
>  struct vfio_device_file *
> -vfio_allocate_device_file(struct vfio_device *device)
> +vfio_allocate_device_file(struct vfio_device *device, bool is_cdev_device)
>  {
>  	struct vfio_device_file *df;
> 
> @@ -407,6 +407,7 @@ vfio_allocate_device_file(struct vfio_device *device)
>  		return ERR_PTR(-ENOMEM);
> 
>  	df->device = device;
> +	df->is_cdev_device = 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.

> 
> +	/*
> +	 * 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 != 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.