I would like to read my CPU's open source drivers. I assume that drivers are located in kernel sources - how can I find out what driver is my CPU using, and where can I find this driver?
Cpu has not drivers! the only thing a cpu has, is a microcode which is usually distributed by INTEL and used as is at boot to patch the microcode of the CPU.
If you want source, you can read the kernel source! which implement kernel mecanism over cpu.
Some part are generic and some others part are specific to the class of cpu you are using (intel alike, risc, arm ....)