It's unfortunate that SKAS0 mode is poorly documented on the User Mode Linux (UML) web site. For example, this page about SKAS doesn't mention it. It is explained in Jeff Dike's UML book though.
I wish they would update the UML web site as it gives the impression that TT and SKAS3 are the only choices, which is no longer true, as SKAS0 was added to the kernel in version 2.6.13.
Here are a handful of resources that I found that describe SKAS0:
