The gathering and analysis of processor traces has been used in computer design and processor architecture research for many decades, but has not been of practical utility in production software — until now. A new facility from Intel, Processor Trace, allows software to gather control-flow traces at low overhead, and it may be possible to analyse and utilise this information within virtual machines for a variety of benefits. In this talk we will describe Processor Trace, how it could be used in VMs, and our progress towards exploiting this mechanism.