[Libguestfs] Double fault panic in L2 upon v2v conversion

[Richard W.M. Jones]

On Thu, Jan 16, 2014 at 11:25:10PM +0200, Rom Freiman wrote:
> Thanks Richard for a fast reply.
> 
> Yes, indeed, im working on a nested environment. I try to run v2v inside a
> VM (L1) and to create an L2 by the conversion process. And on Intel. As I
> wrote, it fails once in few times, mainly when there is a memory pressure
> on L0.
> 
> Kashyap, can you please share your experience? Why should it crash during
> nested conversion. I'm not too familiar with libguestfs logic - maybe you
> can point for me, according to the logs, at what stage of the conversion
> the failure happens.

I can make a general comment here: libguestfs relies on KVM/qemu/etc
being reliable.  If KVM/qemu/etc is broken, then libguestfs isn't
going to work.

If you can't disable nested KVM and don't want to fix it, then you
have two other options:

(1) Patch libguestfs to force qemu to use TCG:

In src/launch-direct.c:
  if (qemu_supports (g, data, "-machine")) {
    ADD_CMDLINE ("-machine");
-   ADD_CMDLINE ("accel=kvm:tcg");
+   ADD_CMDLINE ("accel=tcg");
  } else {

(2) Take a look at the UML backend for libguestfs:

http://libguestfs.org/guestfs.3.html#user-mode-linux-backend

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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