In the six months since Michael's warning here, seabios did indeed strip xen support out of the default binary. So now, in addition to the patch originally included in this bug, this one (actually a modification to an existing debian/patches/ patch) is necessary as well.
Please let me know if there is more information that is needed to get these applied. As a reminder, HVMs are completely broken for any xen compiled with the current packages in jessie/sid.
use-large-seabios.diff
Description: use-large-seabios.diff
