No it doesn't work, at least not for the "jump to the debugger by pressing D" case. Maybe because you only enabled interrupts during traps but not during interrupts? AFAICT there's also some locking/flag setting which might prevent further interrupts while the handler is still running (if I'm looking at the right code, do_IRQ in xen/arch/i386/irq.c).

I considered enabling interrupts at first but I couldn't exclude re-entrance issues. Also I think that it's not the right thing to do in this case: if you're using the debugger on Xen, you don't want interrupts enabled. I think you'd actually want them explicitly disabled (as opposed to the previous/current implicit disabling).