Re: xm save fails to save all pages

[Keir Fraser <keir.xen@gmail.com>]

On 25/10/2011 14:15, "Juergen Gross" <juergen.gross@ts.fujitsu.com> wrote:

> in preparation to support live migration for BS2000 I'm testing my domU (HVM
> with PV-drivers) with xm save/restore. I'm running xen 4.0.2 (from SLES11
> SP1).
> 
> During xm save I see the following line in xend.log:
> 
> [2011-10-25 13:25:25 31519] INFO (XendCheckpoint:484) Saving memory pages:
> iter 1   0%type fail: page 510 mfn 000011fe
> 
> I added some diagnostic code to the hypervisor (in arch/x86/domctl.c) and
> found
> that the hypervisor believes gmfn 11fe of the domU is part of the xen heap.
> 
> The problem is always reported for gmfn 11fe, regardless of the memory size of
> the domU: I tried 1, 2 and 8 GB. The memory page isn't used for anything
> special in the domU, there is no problem accessing it or mapping it to dom0
> before doing the xm save (or after xm save -c).
> 
> When I try to restore the saved domain I can't map gmfn 11fe of the domU any
> longer in dom0 (this was the first hint there is a problem at all).
> 
> How can a domU memory page be part of the xen heap?

It could be the domain's shared-info page, or one of its grant-table pages.
It doesn't make sense to save/restore such pages -- they get reconstructed
appropriately on the receiving end, by the toolstack and/or by the domain
itself when it resumes execution.

 -- Keir