Comment 8 for bug 206864

FYI, passing the kernel boot param 'processor.max_cstate=2' will work ONLY if you have the ACPI Processor compiled into the kernel (aka NOT as a module).
Recompiling the kernel with CONFIG_ACPI_PROCESSOR=y will allow you to set the max_cstate upon boot.

This is probably not an acceptable solution for the majority of users, but it is a workaround.