Hi,
At 10:02 +0800 on 04 Dec (1228384976), Jiang, Yunhong wrote:
> > True, but live-migration doesn't help that because right now given an
> > MFN that's in use as a shadow page or any HVM state page you can't
> > easily find out which domain is responsible for it.
>
> Ahh, yes, didn't realize this. So do you think it is ok to add such
> information?
Maybe for shadow pagetables something could be done, though I'm not sure
there's room in the frametable. I think the other frames are
sufficiently few that if you're already excluding xenheap and dom0 they
won't make much difference.
> > Also, remember that full live-migration needs enough spare RAM to hold
> > an extra copy of the guest, so it couldn't work on guests larger than
> > half the physical RAM, for example.
>
> Yes, that is one argument we thought that before.
>
> >
> >> d) For PV guest, can this be done without co-operation from guest?
> >
> > Yes it can. As long as you don't use the "fast path" resume to restart
> > the guest, it will re-read its p2m just like it would after a full
> > save/restore.
>
> What do you mean of the "fast path"?
Have a look at the code for xc_domain_resume in libxc/xc_resume.c. The
slow-and-safe version makes the domain state look like it would after a
save/restore, so that older kernels can be resumed after they've paused
and had their state saved. The fast version just changes the return
code that the guest will see from its shutdown hypercall.
My suggestion is that you cause the guest to stop like it would for a
save to disk, shuffle its p2m around, and call the slow-path resume
function so that it will pick up the new p2m properly.
> Do you mean the "something very lightweight based on small parts of
> the save/restore code" is done in management tools, not in HV, am I
> right?
Yes. For the common case this lets you get what you want without the
hypervisor being involved.
Cheers,
Tim.
--
Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Principal Software Engineer, Citrix Systems (R&D) Ltd.
[Company #02300071, SL9 0DZ, UK.]
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