Andrea Allievi, Microsoft Spectre and Meltdown CPU have been one of the biggest security problem of the year 2018. Mitigations have already been delivered to the customers by both CPU manufacturers and OS developers. While the mitigations for Spectre type 1 and Meltdown have been successfully delivered, the mitigation for Spectre type 2, Retpoline, has been deferred for various problems. This talk will describe the implementation details of Retpoline in Windows 10 (19H1) and all the problem that we faced while testing it. Designing Retpoline has requested the collaboration of different teams in Microsoft, especially between the Kernel and the Compiler team. This talk will explain how we overcame all the implementation issues and allow all the involved Windows Kernel components to work with Retpoline in a retro-compatible way. At the end we will analyze the performance issues and explain how the Kernel team has found a solution for them