Comment 13 for bug 144631

I was having exactly the same problem, and the above extra line did not help me. However the line:

extra='xencons=tty'

did work for me, and I now have a booted domain that was not previously booting. Please note that this may disable the framebuffer. If you need that you will need to look at xencons=xvc, or at least that is what I think you nee to look at. I do not need the framebuffer, I just came across xvc when trying to figure out what xencons means :-)