Back in May was when Intel published MSAA support for Mesa. The multi-sample anti-aliasing support has since been merged, but now Intel's improving the support for the latest-generation Ivy Bridge graphics.
The CMS part of CMS MSAA is short for "Compressed Multi-sample Surface." With the compression support, MSAA rendering is sped up on Ivy Bridge "Gen7" hardware due to decreased memory bandwidth requirements. The CMS layout is supported for all formats except for signed integer, so uncompressed MSAA is still used there.
The eight CMS MSAA patches for Ivy Bridge (there doesn't appear to be CMS support for Sandy Bridge or prior) can be found on the mesa-dev mailing list until being merged to mainline Mesa.