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:ghostwcy@xxxxxxxxx]
> Sent: 12 June 2015 16:05
> To: Paul Durrant; Wen Congyang; 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
> 
> At 2015/6/12 19:48, Paul Durrant Wrote:
> >> -----Original Message-----
> >> From: Wen Congyang [mailto:wency@xxxxxxxxxxxxxx]
> >> Sent: 12 June 2015 12:10
> >> 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 06:54 PM, Paul Durrant wrote:
> >>>> -----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.
> >>
> >> If the xen is newest, and qemu is old, how is the default ioreq server
> created
> >> for the emulator? Will the old qemu call xc_get_hvm_param(), and the
> >> hypervisor
> >> then creates a default ioreq server?
> >> get is a 'readonly' operation, and creating the default ioreq server in it 
> >> is
> >> very strange.
> >>
> >
> > Might be strange, but that's the way it's done.
> 
> If I only want to get the default ioreq server pfn, and don't want to
> create the default
> ioreq server, how can I do it?

At the moment you can't. If you read the pfns then you will instantiate the 
server, which I agree is a bit of a problem if you're only doing a domain save.

  Paul

> 
> Thanks
> Wen Congyang
> 
> >
> >>>>>
> >>>>>> 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.
> >>
> >> No, only one emulator. Can we run more than one emulator for one hvm
> >> guest? How
> >> to do it?
> >>
> >
> > Yes, more than one emulator can run. There's nothing in libxl to do it, but
> we do it in XenServer using XAPI.
> >
> >>>
> >>>> Is there any application(not emulator) that uses the libxenctrl
> >>>> directly?
> >>>>
> >>>
> >>> What do you mean by application? Toolstacks may use libxenctrl.
> >>
> >> For example: libvirt. I know it uses libxl now. Is there any similar
> application
> >> which uses libxenctrl.
> >
> > Well, XAPI uses it for one.
> >
> >    Paul
> >
> >>
> >> Thanks
> >> Wen Congyang
> >>
> >>>
> >>>    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.
> >>>>>>> .
> >>>>>>>
> >>>>>
> >>>>> .
> >>>>>
> >>>
> >>> .
> >>>
> >
> >
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@xxxxxxxxxxxxx
> > http://lists.xen.org/xen-devel
> >

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