Yesterdays Windows patches have begun to address this vulnerability. The performance impact is noted as limited, but can be more noticeable if you need to disable HyperThreading.
To see whether your system is vulnerable and to what extent, download the MDS Tool found on the middle of this page (https://mdsattacks.com/) and run the relevant executable. If you get an error, install this Visual C++ Redistributable Update and try again. .