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From: Xiao Guangrong <guangrong.xiao@linux.intel.com>
Message-ID: <06340187-61d8-ed7a-e40d-264ca3eb4b37@linux.intel.com>
Date: Wed, 19 Oct 2016 21:39:55 +0800
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Subject: Re: [Qemu-devel] [PATCH 1/2] KVM: page track: add a new notifier
 type: track_flush_slot
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To: Paolo Bonzini <pbonzini@redhat.com>, Xiao Guangrong <guangrong.xiao@intel.com>, Jike Song <jike.song@intel.com>, Alex Williamson <alex.williamson@redhat.com>
Cc: "Tian, Kevin" <kevin.tian@intel.com>, Neo Jia <cjia@nvidia.com>, kvm@vger.kernel.org, qemu-devel <qemu-devel@nongnu.org>, Xiaoguang Chen <xiaoguang.chen@intel.com>, Kirti Wankhede <kwankhede@nvidia.com>



On 10/19/2016 07:56 PM, Paolo Bonzini wrote:
>
>
> On 19/10/2016 07:45, Xiao Guangrong wrote:
>>
>>
>> On 10/19/2016 10:32 AM, Jike Song wrote:
>> +EXPORT_SYMBOL_GPL(vfio_group_set_usrdata);
>>>>> +
>>>>> +void *vfio_group_get_usrdata(struct vfio_group *group)
>>>>> +{
>>>>> +    return group->usrdata;
>>>>> +}
>>>>> +EXPORT_SYMBOL_GPL(vfio_group_get_usrdata);
>>>>> +
>>>>> +void *vfio_group_get_usrdata_by_device(struct device *dev)
>>>>> +{
>>>>> +    struct vfio_group *vfio_group;
>>>>> +
>>>>> +    vfio_group = __vfio_group_get_from_iommu(dev->iommu_group);
>>>>
>>>> We actually need to use iommu_group_get() here.  Kirti adds a
>>>> vfio_group_get_from_dev() in v9 03/12 that does this properly.
>>>>
>>>>> +    if (!vfio_group)
>>>>> +        return NULL;
>>>>> +
>>>>> +    return vfio_group_get_usrdata(vfio_group);
>>
>> I am worrying if the kvm instance got from group->usrdata is safe
>> enough? What happens if you get the instance after kvm released
>> kvm-vfio device?
>
> It shouldn't happen if you use kvm_get_kvm and kvm_put_kvm properly.  It
> is almost okay in the patch, just:
>

How about if KVM releases kvm-vfio device between vfio_group_get_usrdata()
and get_kvm()?