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

[Wen Congyang <wency@xxxxxxxxxxxxxx>]

On 06/12/2015 03:41 PM, Paul Durrant wrote:
>> -----Original Message-----
>> From: Wen Congyang [mailto:wency@xxxxxxxxxxxxxx]
>> Sent: 12 June 2015 04:22
>> To: Paul Durrant; Yang Hongyang; Andrew Cooper; xen-devel@xxxxxxxxxxxxx
>> Cc: Wei Liu; Ian Campbell; guijianfeng@xxxxxxxxxxxxxx;
>> yunhong.jiang@xxxxxxxxx; Eddie Dong; rshriram@xxxxxxxxx; 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@xxxxxxxxxxxxxx]
>>>> Sent: 11 June 2015 13:59
>>>> To: Paul Durrant; Wen Congyang; Andrew Cooper; xen-
>> devel@xxxxxxxxxxxxx
>>>> Cc: Wei Liu; Ian Campbell; guijianfeng@xxxxxxxxxxxxxx;
>>>> yunhong.jiang@xxxxxxxxx; Eddie Dong; rshriram@xxxxxxxxx; 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@xxxxxxxxxxxxxx]
>>>>>> Sent: 11 June 2015 09:48
>>>>>> To: Paul Durrant; Andrew Cooper; Yang Hongyang; xen-
>>>> devel@xxxxxxxxxxxxx
>>>>>> Cc: Wei Liu; Ian Campbell; guijianfeng@xxxxxxxxxxxxxx;
>>>> [...]
>>>>>
>>>>>>
>>>>>> 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@xxxxxxxxxxxxx
>>>>>>>>>> http://lists.xen.org/xen-devel
>>>>>>>>>
>>>>>>>>> _______________________________________________
>>>>>>>>> Xen-devel mailing list
>>>>>>>>> Xen-devel@xxxxxxxxxxxxx
>>>>>>>>> http://lists.xen.org/xen-devel
>>>>>>>>> .
>>>>>>>>>
>>>>>>>
>>>>>>> .
>>>>>>>
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> Xen-devel mailing list
>>>>> Xen-devel@xxxxxxxxxxxxx
>>>>> http://lists.xen.org/xen-devel
>>>>> .
>>>>>
>>>>
>>>> --
>>>> Thanks,
>>>> Yang.
>>> .
>>>
> 
> .
> 


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