[Xen-devel] Migration of a 32-bit PV-Guest

[Vasco Fachin <pdpcrew@xxxxxxxxx>]

Hi everybody,

I am currently working on a object-oriented paravirtual operating
system as a university project.

We were able to use a MiniOS core in order to build a relative stable
guest, or at least stable enough for our purposes. :-D

However for one thing we could not proceed. We need to migrate our
guest to another machine, so after some research we came by this
hypercall: HYPERVISOR_update_va_mapping(...), which is apparently
needed in order to unmap the shared info page before we could suspend
our system.

At this point, our system crashes everytime with the following output
from "xm dmesg":
(XEN) mm.c:918:d320 Error getting mfn 4636 (pfn 5555555555555555) from
L1 entry 0000000004636023 for l1e_owner=320, pg_owner=320

I tested the same hypercall with a 32bit version of MiniOS and it
crashes as well with the same output. Then I tried it with a 64bit
version of MiniOS and seems to work just fine.

Somehow I cannot find any 32bit paravirtual machine that could be
migrated. Does anybody know if such a system exists?

Our configuration at the moment is this:
Dom0: Ubuntu 12.10 64bit
XEN: xen 4.1.4 64bit
DomU: 32bit PV-Guest (Object-oriented derived from a 32bit version of MiniOS).

We tested our system, with the same behavior, also on the following platform:
Dom0: Ubuntu 12.04 32bit
XEN: xen 4.1.4 32bit

My question is: does anybody know if a migration of a 32bit PV-System
is possible (in Xen 4.1.4/any newer release)? Or has anyone an idea of
why this particular hypercall fails to execute on a 32bit guest, while
it works on a 64bit guest?

I of course don't ask for a solution of our problem, but maybe someone
came by the same kind of problem and can point me in the right
direction?

Thank you very much in advance!

Best regards,

Vasco Fachin

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