On my MacBookPro11,1 I installed 14.10 beta-2 and have the same problem. Booting from usb works, booting from harddisk not (after installation), booting from harddisk while passing nr_cpus=1 on kernel cmdline works (but only works with 1 core, obviously).
On my MacBookPro11,1 I installed 14.10 beta-2 and have the same problem. Booting from usb works, booting from harddisk not (after installation), booting from harddisk while passing nr_cpus=1 on kernel cmdline works (but only works with 1 core, obviously).