[Intel-gfx] [PATCH v3 14/15] vfio: Add ioctls for device cdev using iommufd

[Yan Zhao]

On Thu, Feb 16, 2023 at 05:10:06PM +0800, Liu, Yi L wrote:
> > From: Zhao, Yan Y <yan.y.zhao at intel.com>
> > Sent: Thursday, February 16, 2023 4:24 PM
> > 
> > On Mon, Feb 13, 2023 at 07:13:47AM -0800, Yi Liu wrote:
> > ...
> > 
> > > +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;
> > > +	struct fd f;
> > > +	unsigned long minsz;
> > > +	int ret;
> > > +
> > > +	minsz = offsetofend(struct vfio_device_bind_iommufd, out_devid);
> > > +
> > > +	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;
> > > +
> > > +	ret = vfio_device_claim_group(device);
> > > +	if (ret)
> > > +		return ret;
> > > +
> > > +	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);
> > Here, the iommufd file count + 1,
> > 
> > > +		if (!f.file) {
> > > +			ret = -EBADF;
> > > +			goto out_unlock;
> > > +		}
> > > +		iommufd = iommufd_ctx_from_file(f.file);
> > iommufd file count + 1, again
> > 
> > > +		if (IS_ERR(iommufd)) {
> > > +			ret = PTR_ERR(iommufd);
> > > +			goto out_put_file;
> > > +		}
> > > +	}
> > > +
> > > +	/*
> > > +	 * Before the 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);
> > iommufd file count + 1 in iommufd_device_bind for first open.
> > 
> > > +	if (ret)
> > > +		goto out_put_kvm;
> > > +
> > > +	ret = copy_to_user((void __user *)arg +
> > > +			   offsetofend(struct vfio_device_bind_iommufd,
> > iommufd),
> > > +			   &bind.out_devid,
> > > +			   sizeof(bind.out_devid)) ? -EFAULT : 0;
> > > +	if (ret)
> > > +		goto out_close_device;
> > > +
> > > +	if (iommufd)
> > > +		fdput(f);
> > But, only one file count is put.
> 
> Good catch! Yes it is missed. And needs to call iommufd_ctx_put()
> in vfio_device_cdev_close() as well.
If I read correctly, iommufd_device_bind() in the first open will
get the reference through iommufd_ctx_get(ictx) and 
iommufd_device_destroy() in the last close will do the iommufd_ctx_put().

As vfio_device_ioctl_bind_iommufd() isn't paring with
vfio_device_cdev_close(), I think the fix below is simpler :) 

> > Need a paring iommufd_ctx_put() after a successful
> > iommufd_ctx_from_file()
> > above to avoid iommufd_fops_release() never being called.
> > 
> > e.g.
> > 
> > @@ -1222,11 +1226,13 @@ static long
> > vfio_device_ioctl_bind_iommufd(struct vfio_device_file *df,
> >                         ret = -EBADF;
> >                         goto out_unlock;
> >                 }
> >                 iommufd = iommufd_ctx_from_file(f.file);
> >                 if (IS_ERR(iommufd)) {
> >                         ret = PTR_ERR(iommufd);
> >                         goto out_put_file;
> >                 }
> > +               iommufd_ctx_put(iommufd);
> 
> Since iommufd is recorded in df, so needs to hold refcount till
> df->iommufd=NULL;
> 
> 
> >         }
> > 
> >         /* df->kvm is supposed to be set in vfio_device_file_set_kvm() */
> > 
> > > +	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);
> > > +out_put_kvm:
> > > +	df->iommufd = NULL;
> > > +	df->noiommu = false;
> > > +	vfio_device_put_kvm(device);
> > > +out_put_file:
> > > +	if (iommufd)
> > > +		fdput(f);
> > > +out_unlock:
> > > +	mutex_unlock(&device->dev_set->lock);
> > > +	vfio_device_release_group(device);
> > > +	return ret;
> > > +}
> > > +