From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1161190AbcKAFcX (ORCPT <rfc822;w@1wt.eu>);
        Tue, 1 Nov 2016 01:32:23 -0400
Received: from mga11.intel.com ([192.55.52.93]:54653 "EHLO mga11.intel.com"
        rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
        id S1034388AbcKAFcV (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
        Tue, 1 Nov 2016 01:32:21 -0400
X-ExtLoop1: 1
X-IronPort-AV: E=Sophos;i="5.31,430,1473145200"; 
   d="scan'208";a="26343930"
Message-ID: <58182819.2050109@intel.com>
Date: Tue, 01 Nov 2016 13:28:57 +0800
From: Jike Song <jike.song@intel.com>
User-Agent: Mozilla/5.0 (X11; Linux i686 on x86_64; rv:17.0) Gecko/20130801 Thunderbird/17.0.8
MIME-Version: 1.0
To: Alex Williamson <alex.williamson@redhat.com>
CC: Kirti Wankhede <kwankhede@nvidia.com>, pbonzini@redhat.com,
        kraxel@redhat.com, cjia@nvidia.com, qemu-devel@nongnu.org,
        kvm@vger.kernel.org, kevin.tian@intel.com, bjsdjshi@linux.vnet.ibm.com,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v10 01/19] vfio: Mediated device Core driver
References: <1477517366-27871-1-git-send-email-kwankhede@nvidia.com> <1477517366-27871-2-git-send-email-kwankhede@nvidia.com> <5818071F.3020507@intel.com> <20161031214453.49da775c@t450s.home>
In-Reply-To: <20161031214453.49da775c@t450s.home>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On 11/01/2016 11:44 AM, Alex Williamson wrote:
> On Tue, 01 Nov 2016 11:08:15 +0800
> Jike Song <jike.song@intel.com> wrote:
>> On 10/27/2016 05:29 AM, Kirti Wankhede wrote:
>>> +static int mdev_attach_iommu(struct mdev_device *mdev)
>>> +{
>>> +	int ret;
>>> +	struct iommu_group *group;
>>> +
>>> +	group = iommu_group_alloc();
>>> +	if (IS_ERR(group))
>>> +		return PTR_ERR(group);  
>>
>> Maybe I overthought, but where the iommu_group is released? On successful
>> return you already have a ref, I didn't find an iommu_group_put after that.
> ...
>>> +
>>> +	ret = iommu_group_add_device(group, &mdev->dev);
>>> +	if (ret)
>>> +		goto attach_fail;
>>> +
>>> +	dev_info(&mdev->dev, "MDEV: group_id = %d\n",
>>> +				 iommu_group_id(group));
>>> +attach_fail:
>>> +	iommu_group_put(group);
>>> +	return ret;
>>> +}
>>> +
>>> +static void mdev_detach_iommu(struct mdev_device *mdev)
>>> +{
>>> +	iommu_group_remove_device(&mdev->dev);
> 
> Here.  Adding a device to the group takes a group reference so we can
> 'put' the group to release the reference from the alloc as soon as a
> device is added.  When we remove the device, that reference is removed
> and this should result in a release of the group if all other
> references are balanced.  Thanks,

Now I understand, thanks :)

--
Thanks,
Jike