linux-kernel - RE: [PATCH v2 13/14] vfio: Add ioctls for device cdev using iommufd

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Date:   Tue, 7 Feb 2023 07:50:40 +0000
From:   "Liu, Yi L" <yi.l.liu@...el.com>
To:     "Zhao, Yan Y" <yan.y.zhao@...el.com>
CC:     "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "jgg@...dia.com" <jgg@...dia.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
        "yi.y.sun@...ux.intel.com" <yi.y.sun@...ux.intel.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "mjrosato@...ux.ibm.com" <mjrosato@...ux.ibm.com>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        "cohuck@...hat.com" <cohuck@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "peterx@...hat.com" <peterx@...hat.com>,
        "eric.auger@...hat.com" <eric.auger@...hat.com>,
        "nicolinc@...dia.com" <nicolinc@...dia.com>,
        "shameerali.kolothum.thodi@...wei.com" 
        <shameerali.kolothum.thodi@...wei.com>,
        "suravee.suthikulpanit@....com" <suravee.suthikulpanit@....com>,
        "chao.p.peng@...ux.intel.com" <chao.p.peng@...ux.intel.com>,
        "lulu@...hat.com" <lulu@...hat.com>,
        "intel-gvt-dev@...ts.freedesktop.org" 
        <intel-gvt-dev@...ts.freedesktop.org>,
        "intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>
Subject: RE: [PATCH v2 13/14] vfio: Add ioctls for device cdev using iommufd

> From: Yan Zhao <yan.y.zhao@...el.com>
> Sent: Tuesday, February 7, 2023 11:41 AM
> 
> On Mon, Feb 06, 2023 at 01:05:31AM -0800, Yi Liu wrote:
> ...
> 
> > +void vfio_device_cdev_close(struct vfio_device_file *df)
> > +{
> > +	mutex_lock(&df->device->dev_set->lock);
> > +	vfio_device_close(df);
> > +	vfio_device_put_kvm(df->device);
> > +	mutex_unlock(&df->device->dev_set->lock);
> > +}
> > +
> 
> ...
> 
> > +long vfio_device_ioctl_bind_iommufd(struct vfio_device_file *df,
> > +				    unsigned long arg)
> > +{
> > +	struct vfio_device *device = df->device;
> > +	struct vfio_device_bind_iommufd bind;
> > +	struct iommufd_ctx *iommufd = NULL;
> > +	unsigned long minsz;
> > +	struct fd f;
> > +	int ret;
> > +
> > +	minsz = offsetofend(struct vfio_device_bind_iommufd, iommufd);
> > +
> > +	if (copy_from_user(&bind, (void __user *)arg, minsz))
> > +		return -EFAULT;
> > +
> > +	if (bind.argsz < minsz || bind.flags)
> > +		return -EINVAL;
> > +
> > +	if (!device->ops->bind_iommufd)
> > +		return -ENODEV;
> > +
> > +	mutex_lock(&device->dev_set->lock);
> > +	/*
> > +	 * If already been bound to an iommufd, or already set noiommu
> > +	 * then fail it.
> > +	 */
> > +	if (df->iommufd || df->noiommu) {
> > +		ret = -EINVAL;
> > +		goto out_unlock;
> > +	}
> > +
> > +	/* iommufd < 0 means noiommu mode */
> > +	if (bind.iommufd < 0) {
> > +		if (!capable(CAP_SYS_RAWIO)) {
> > +			ret = -EPERM;
> > +			goto out_unlock;
> > +		}
> > +		df->noiommu = true;
> > +	} else {
> > +		f = fdget(bind.iommufd);
> > +		if (!f.file) {
> > +			ret = -EBADF;
> > +			goto out_unlock;
> > +		}
> > +		iommufd = iommufd_ctx_from_file(f.file);
> > +		if (IS_ERR(iommufd)) {
> > +			ret = PTR_ERR(iommufd);
> > +			goto out_put_file;
> > +		}
> > +	}
> > +
> > +	/*
> > +	 * Before the first device open, get the KVM pointer currently
> > +	 * associated with the device file (if there is) and obtain a
> > +	 * reference. This reference is held until device closed. Save
> > +	 * the pointer in the device for use by drivers.
> > +	 */
> > +	vfio_device_get_kvm_safe(df);
> > +
> > +	df->iommufd = iommufd;
> > +	ret = vfio_device_open(df, &bind.out_devid, NULL);
> > +	if (ret)
> > +		goto out_put_kvm;
> > +
> > +	ret = copy_to_user((void __user *)arg + minsz,
> > +			   &bind.out_devid,
> > +			   sizeof(bind.out_devid)) ? -EFAULT : 0;
> > +	if (ret)
> > +		goto out_close_device;
> > +
> > +	if (iommufd)
> > +		fdput(f);
> > +	else if (df->noiommu)
> > +		dev_warn(device->dev, "vfio-noiommu device used by user
> "
> > +			 "(%s:%d)\n", current->comm,
> task_pid_nr(current));
> > +	mutex_unlock(&device->dev_set->lock);
> > +	return 0;
> > +
> > +out_close_device:
> > +	vfio_device_close(df);
> vfio_device_close() is called here if any error after vfio_device_open().
> But it will also be called unconditionally in vfio_device_cdev_close() and
> cause a wrong value of device->open_count.

Oh, yes yes. Good catch. Vfio_device_cdev_close() should check either the
open_count or access_granted.

> df->access_granted in patch 07 can also be of wrong true value after
> this vfio_device_close().

access_granted will surely be wrong if open_count is not correctly
counted.

Regards,
Yi Liu