linux-kernel - Re: [PATCH v10 01/19] vfio: Mediated device Core driver

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Date:   Mon, 31 Oct 2016 21:44:53 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Jike Song <jike.song@...el.com>
Cc:     Kirti Wankhede <kwankhede@...dia.com>, pbonzini@...hat.com,
        kraxel@...hat.com, cjia@...dia.com, qemu-devel@...gnu.org,
        kvm@...r.kernel.org, kevin.tian@...el.com,
        bjsdjshi@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v10 01/19] vfio: Mediated device Core driver

On Tue, 01 Nov 2016 11:08:15 +0800
Jike Song <jike.song@...el.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,

Alex

> > +	dev_info(&mdev->dev, "MDEV: detaching iommu\n");
> > +}
> > +  
>