kvm (native or otherwise) runs a plain, vanilla Linux as its guest OS. UML on the other hand is quite heavily modified. It may also lag the current kernel.
For testing your kernel-patch-du-jour, kvm is most certainly the better choice.
Posted Aug 31, 2011 15:16 UTC (Wed) by nix (subscriber, #2304)
[Link]
What? UML is just another architecture, that is all. It's upstream: it is not meaningful to say that it is 'heavily modified' or that it 'may lag', any more than any other userspace program 'may lag'. If you want a matching version, compile with ARCH=um and you have it.