Great article:

https://www.cyberciti.biz/faq/check-linux-server-for-spectre-meltdown-vulnerability/

Intel has also released a microcode update:

https://downloadcenter.intel.com/download/27431/Linux-Processor-Microcode-Data-File

How does it affect performance on Windows systems? According to Microsoft:

https://cloudblogs.microsoft.com/microsoftsecure/2018/01/09/understanding-the-performance-impact-of-spectre-and-meltdown-mitigations-on-windows-systems/

#Update 1/17/2018 Tool for checking on Windows systems:

http://www.guru3d.com/news-story/download-inspectre-meltdown-and-spectre-check-tool.html

sha1sum ‘[Guru3D]-InSpectre.exe’
6a3f1382f3c9c1fd53bf4c3708e3a449cbcb136f [Guru3D]-InSpectre.exe