I'm currently using VirtualBox on my Linux server to run a small Windows guest OS. I've configured its main virtual hard drive as what VBox calls "Immutable" - meaning that any changes to it are written into a differencing image that is discarded when the system reboots.

Can KVM do something similar?

I've read about snapshots via "savevm", "loadvm" but I believe that's saved states, not differencing images.

What I ultimately want is a VM with two drives: one reverts on each reboot, one keeps its changes. Ideally, the unchangeable drive image should be stored with only read access granted to the user running KVM.