Haswell undervolting

[matyas]

I've put in some time into looking for how to undervolt Haswell (e.g. 4800MQ) under Linux, but have not found anything beside PHCTool (which seems to be outdated).
Has anyone been able to undervolt their Intel CPU under Linux? Even if it is the 3rd generation, as it may still apply to Linux. Under Windows, Intel XTU can be used...

Thanks!