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

[Jike Song]

On 10/21/2016 01:19 AM, Xiao, Guangrong wrote:
>> On 10/19/2016 10:14 PM, Paolo Bonzini wrote:
>>> On 19/10/2016 15:39, Xiao Guangrong wrote:
>>>
>>>
>>> I understood that KVM side is safe, however, vfio side is independent 
>>> with kvm and the user of usrdata can fetch kvm struct at any time, 
>>> consider this scenario:
>>>
>>> CPU 0                         CPU 1
>>> KVM:                         VFIO/userdata user
>>>   kvm_ioctl_create_device
>>>      get_kvm()
>>>                             vfio_group_get_usrdata(vfio_group)
>>>   kvm_device_release
>>>     put_kvm()
>>>                             !!! kvm refcount has gone
>>>                             use KVM struct
>>>
>>> Then, the user of userdata have fetched kvm struct but the refcount 
>>> has already gone.
>> 
>> vfio_group_set_usrdata (actually) kvm_vfio_group_set_kvm has called
>>kvm_get_kvm too, however.  What you need is a mutex that is taken by
>>vfio_group_set_usrdata and by the callers of vfio_group_get_usrdata.
> 
> Yes, mutex can fix it and is good to me. :)

Thanks everyone, I'll cook another patch according to your guidance.

--
Thanks,
Jike