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

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Wen Congyang [mailto:wency@xxxxxxxxxxxxxx]
> Sent: 12 June 2015 11:26
> 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 06/12/2015 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?

You mean a secondary emulator? Yes, that's why there is the notion of default 
ioreq server... to allow a secondary emulator to be used even when an old QEMU 
is in use.

> Is there any application(not emulator) that uses the libxenctrl
> directly?
> 

What do you mean by application? Toolstacks may use libxenctrl.

  Paul

> 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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