Comment 28 for bug 355232

That canned response doesn't apply, as the problem is not in the kernel itself, but in the configuration Ubuntu is using to compile the kernel.

The fix is simple: in the kernel config, change

CONFIG_X86_POWERNOW_K8=y

and

CONFIG_X86_ACPI_CPUFREQ=y

to

CONFIG_X86_POWERNOW_K8=m

and

CONFIG_X86_ACPI_CPUFREQ=m

respectively.

Confirmed in Trusty Tahr. Boy this guy's been around.