Re: [PATCH v2 COLOPre 03/13] libxc/restore: zero ioreq page only one time

[Wen Congyang <wency@cn.fujitsu.com>]

On 06/12/2015 03:41 PM, Paul Durrant wrote:
>> -----Original Message-----
>> From: Wen Congyang [mailto:wency@cn.fujitsu.com]
>> Sent: 12 June 2015 04:22
>> To: Paul Durrant; Yang Hongyang; Andrew Cooper; xen-devel@lists.xen.org
>> Cc: Wei Liu; Ian Campbell; guijianfeng@cn.fujitsu.com;
>> yunhong.jiang@intel.com; Eddie Dong; rshriram@cs.ubc.ca; Ian Jackson
>> Subject: Re: [Xen-devel] [PATCH v2 COLOPre 03/13] libxc/restore: zero ioreq
>> page only one time
>>
>> On 06/11/2015 09:25 PM, Paul Durrant wrote:
>>>> -----Original Message-----
>>>> From: Yang Hongyang [mailto:yanghy@cn.fujitsu.com]
>>>> Sent: 11 June 2015 13:59
>>>> To: Paul Durrant; Wen Congyang; Andrew Cooper; xen-
>> devel@lists.xen.org
>>>> Cc: Wei Liu; Ian Campbell; guijianfeng@cn.fujitsu.com;
>>>> yunhong.jiang@intel.com; Eddie Dong; rshriram@cs.ubc.ca; Ian Jackson
>>>> Subject: Re: [Xen-devel] [PATCH v2 COLOPre 03/13] libxc/restore: zero
>> ioreq
>>>> page only one time
>>>>
>>>>
>>>>
>>>> On 06/11/2015 06:20 PM, Paul Durrant wrote:
>>>>>> -----Original Message-----
>>>>>> From: Wen Congyang [mailto:wency@cn.fujitsu.com]
>>>>>> Sent: 11 June 2015 09:48
>>>>>> To: Paul Durrant; Andrew Cooper; Yang Hongyang; xen-
>>>> devel@lists.xen.org
>>>>>> Cc: Wei Liu; Ian Campbell; guijianfeng@cn.fujitsu.com;
>>>> [...]
>>>>>
>>>>>>
>>>>>> In our implementation, we don't start a new emulator. The codes can
>>>> work,
>>>>>> but some bugs may be not triggered.
>>>>>>
>>>>>
>>>>> How do you reconcile the incoming QEMU save record with the running
>>>> emulator state?
>>>>
>>>> We introduce a qmp command "xen-load-devices-
>>>> state"(libxl__qmp_restore) which
>>>> can restore the emulator state. The step of resotre emulator state at a
>>>> checkpoint is:
>>>>
>>>> 1. libxl__qmp_stop    -> vm_stop() in qemu
>>>> 2. libxl__qmp_restore -> load_vmstate() in qemu
>>>> 3. libxl__qmp_resume  -> vm_start() in qemu
>>>>
>>>
>>> Ok, that sounds like the ideal time to hook back into Xen by creating a new
>> ioreq server.
>>
>> I have some questions about ioreq server:
>> 1. If we use old version xen and newest version qemu, is it OK? Is default
>>    ioreq server created when the guest is created. xen_create_ioreq_server()
>> does
>>    nothing, and xen_get_ioreq_server_info() will get the default ioreq server
>> information.
>>    Is it right?
> 
> No. It's not compatible in that direction. A new Xen will work with an old QEMU but not the other way round.
> 
>> 2. Why we create a default ioreq server when getting the hvm param if there
>> is already a
>>    not default ioreq server?
> 
> If something reads the 'legacy' HVM params then that is Xen's trigger to create the default server. Any 'new' emulator should be using the ioreq server hypercalls so the default server will not be needed.

If there are two ioreq servers: default ioreq server, and a ioreq server created by emulator. The guest can work it correctly in
this case? Is there any application(not emulator) that uses the libxenctrl directly?

Thanks
Wen Congyang

> 
>> 3. In the far end, we will clear the ioreq page, and this ioreq page is used for
>> default
>>    ioreq server, is it right?
> 
> Yes, AFAIK it's only the 'magic' pages that get cleared at the far end - and that includes the default server pages. Other ioreq servers will have their pages cleared on re-insertion to the P2M at the source end when the server is disabled.
> 
>   Paul
> 
>>
>> Thanks
>> Wen Congyang
>>
>>>
>>>   Paul
>>>
>>>>>
>>>>>    Paul
>>>>>
>>>>>> Thanks
>>>>>> Wen Congyang
>>>>>>
>>>>>>>
>>>>>>>    Paul
>>>>>>>
>>>>>>>>
>>>>>>>> Thanks
>>>>>>>> Wen Congyang
>>>>>>>>
>>>>>>>>>
>>>>>>>>>    Paul
>>>>>>>>>
>>>>>>>>>> We will set to the guest to a new state, the old state should be
>>>>>> dropped.
>>>>>>>>>>
>>>>>>>>>> Thanks
>>>>>>>>>> Wen Congyang
>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>    Paul
>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>> Thanks
>>>>>>>>>>>> Wen Congyang
>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>>    Paul
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>>> Thanks
>>>>>>>>>>>>>> Wen Congyang
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> ~Andrew
>>>>>>>>>>>>>>> .
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>> .
>>>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> .
>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> _______________________________________________
>>>>>>>>>> Xen-devel mailing list
>>>>>>>>>> Xen-devel@lists.xen.org
>>>>>>>>>> http://lists.xen.org/xen-devel
>>>>>>>>>
>>>>>>>>> _______________________________________________
>>>>>>>>> Xen-devel mailing list
>>>>>>>>> Xen-devel@lists.xen.org
>>>>>>>>> http://lists.xen.org/xen-devel
>>>>>>>>> .
>>>>>>>>>
>>>>>>>
>>>>>>> .
>>>>>>>
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> Xen-devel mailing list
>>>>> Xen-devel@lists.xen.org
>>>>> http://lists.xen.org/xen-devel
>>>>> .
>>>>>
>>>>
>>>> --
>>>> Thanks,
>>>> Yang.
>>> .
>>>
> 
> .
>