TCG does not support x2APIC emulation
This is not a bug so much as a feature request.
It would be great if there was a pure-software emulation of the x2APIC on x86_64, so that it could be used on systems that don't support such providing a thing on via a host-based solution (e.g., KVM etc). KVM provides this, but that doesn't help if you're working on a machine that doesn't support KVM.
[formerly bug #1877781 on Launchpad]