Shared value between host and guests

[Genevieve Bastien <gbastien@versatic.net>]

Hi,

I'm tracing kvm guests and their host and an issue we have is to
identify which host process corresponds to which guest trace so we can
follow the state of the virtual cpu on the host.

For our needs, we fixed this problem by adding a kernel module on host
and guest where hosts and guests make an hypercall received by the other
and sending a UID between them. By tracing those hypercalls and tracking
the uid value, we can know which thread on the host corresponds to which
guest machine.

But we would like to achieve this without having to add an additional
module for tracing purposes. I'm wondering if there's already a value
somewhere in the kernel that is uniquely shared between the host
process/threads and the corresponding guest. And if not, would it be
possible/desirable to add one? For instance, the bootid of the guest
could be sent to the host process at the start and stored in some system
file. The trace could then retrieve it and the analysis can figure out
who's who all the traces.

Fyi, this is the kind of virtual machine analyses we can obtain by
tracing guest and host:
http://archive.eclipse.org/tracecompass.incubator/doc/org.eclipse.tracecompass.incubator.virtual.machine.analysis.doc.user/Virtual-Machine-Analysis-User-Documentation.html 
We have more, but it is not yet documented unfortunately.

Thanks,
Geneviève