Re: [Qemu-devel] [PATCH 1/2] KVM: page track: add a new notifier type: track_flush_slot

[Paolo Bonzini]

On 19/10/2016 15:39, Xiao Guangrong wrote:
> 
> 
> 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()?

That cannot happen as long as there is a struct file* for the device
(see kvm_ioctl_create_device and kvm_device_release).  Since you're
sending a ioctl to it, it's fine.

Paolo