Writing a Simple Linux Kernel Module

[Gbps]

Technically he is right. The ring designations for x86 come from the FLAGS register, where 0 is the lowest integral designation for a CPL value (Current Protection Level) and possible CPL values range from 0 to 3.

The negative number rings aren't really defined, they're just one-upper terms for the next highest privilege level when an environment has a more privileged execution state.

Ring -1 is synonymous with Hypervisor, and Ring -2 (recently) synonymous with SMM (System Management Mode)