There is a new guidance document from Intel here https://newsroom.intel.com/wp-content/uploads/sites/11/2018/04/microcode-update-guidance.pdf Changes since the previous release are highlighted in yellow. Unfortunately, the latest microcode here https://downloadcenter.intel.com/download/27591/Linux-Processor-Microcode-Data-File?product=873 does not seem to contain all the yellow updates (at least for my hardware). The document is from April 2 and the latest microcode update is from March 12.