Re: [Xen-devel] live migration question

[Juergen Gross <juergen.gross@xxxxxxxxxxxxxx>]

On 01/31/2012 08:50 AM, Juergen Gross wrote:
> On 01/30/2012 05:26 PM, Jan Beulich wrote:
> > > > > On 30.01.12 at 13:24, Juergen Gross<juergen.gross@xxxxxxxxxxxxxx>  wrote:
> > > To avoid this stall I tried to start a little daemon on the target machine
> > > and watch for a new BS2000 domain to show up due to live migration. I wanted
> > > to map the domain memory as soon as the needed mapping information located
> > > in a fixed guest mfn was transferred. Discovery of the new domain works as
> > > expected, but I'm not capable doing any memory mapping until the restore of
> > > the domain is finished. The mapping ioctl using IOCTL_PRIVCMD_MMAP returns
> > > EINVAL until xc_restore is finished (more or less).
> > >
> > > Why can xc_restore do the mapping while I can't? I know xc_restore is using
> > > IOCTL_PRIVCMD_MMAPBATCH_V2, but I can't see a difference which should matter
> > > between those two, as both are using the same hypercall to update the dom0
> > > page tables.
> > I cannot immediately think of a reason (and indeed the difference
> > between the two is only how errors get handled), so I wonder
> > whether you checked where the - pretty generic - -EINVAL is
> > coming from. You also didn't mention whether any hypervisor log
> > entries are associated with you failed attempts.
> I'll start to add some logging to the hypervisor today.
>
> No hypervisor logs were produced in my tests, despite of setting
>
> debug=yes loglvl=all guest_loglvl=all
>
> as boot parameters.
>
> I've made an additional test using xm save/xm restore to see if the same
> problem shows up. It does NOT. Mapping succeeds at once while restoring
> memory is still running. I always thought xm restore and live migration on
> the target machine are more or less the same. This seems not to be true.
Okay, here are my results (so far):

do_mmu_update() calls mod_l1_entry() which fails with -EINVAL due to an
invalid mfn and p2m-type == 4 returned by:

mfn_x(gfn_to_mfn(pg_dom, l1e_get_pfn(nl1e), &p2mt))

I still don't see why xc_restore is able to do the mapping while my daemon is
not. And I can't find any difference between a domain creation due to
xm restore and a live migration.


Juergen

--
Juergen Gross                 Principal Developer Operating Systems
PDG ES&S SWE OS6                       Telephone: +49 (0) 89 3222 2967
Fujitsu Technology Solutions              e-mail: juergen.gross@xxxxxxxxxxxxxx
Domagkstr. 28                           Internet: ts.fujitsu.com
D-80807 Muenchen                 Company details: ts.fujitsu.com/imprint.html


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