For several years I have run both the Knoppix ISO-image and disk-based versions under kvm for installs, maintenance etc. The basic method works for 8.3 too, but only as far as the first flash install.
Klaus K has made Knoppix more "fool-proof" to run under kvm by restricting it to read-only mode. For many users, that is clearly a feature: You may run your ordinary Knoppix install under kvm so it functions as both host and guest at once, but if persistent store is involved, and the host and the guest instances perform different updates to that, then what?
It is only a question of time until the file system is corrupted - it is easy to imagine that prof. Knopper has introduced this restriction from experiences with broken systems.
The bug is that it doesn't stop there. If you run different copies of Knoppix on different partitions, or run Knoppix under another OS variety, even another version of Knoppix, the only thing to be careful about is that the partition where the persistent store of the VM resides is not writable by other OS'es. But don't try to explain that to Knoppix 8.3. It only checks whether it is run under kvm, and in that case, the system is mounted read-only. Which kind of blocks many important uses of Knoppix images.
While the default behaviour is "correct", there must be a cheatcode for disabling it, e.g. VIRTWRITE. I guess specialists on minirt.gz should not have too much problems rolling their own, but this is a general issue, so for me it belongs in Knopper-land proper.
Dell PowerEdge R720 Server - 2x8c CPU,256Gb RAM, 128Gb SSD/3x900Gb SAS, Proxmox
$340.00
Supermicro 4U 36 Bay Storage Server 2.4Ghz 8-C 128GB 1x1280W Rails TrueNAS ZFS
$712.98
CSE-118 Supermicro 1U 3x GPU Server 2.6Ghz 20-C 128GB CX353A 2x1600W PSU Rails
$454.03
Dell PowerEdge R630 8SFF 2.6Ghz 20-Core 128GB Mem 2x10G+2x1G NIC 2x750W PSU
$399.04
Intel Xeon Gold 6140 SR3AX 2.3GHz 18-Core Processor CPU
$39.99
Intel Xeon E5-2697A V4 2.6GHz CPU Processor 16-Core Socket LGA2011 SR2K1
$39.99
Intel Xeon E5-2680 v4 2.4GHz 35MB 14-Core 120W LGA2011-3 SR2N7
$17.99
SR1XP Intel Xeon E5-2680 v3 12 Core 30MB 2.5GHz LGA 2011-3 A Grade Processor
$5.09
Dell Precision T5600/t5610 Xeon E5-2670 2.6Ghz 16GB DDR3 RAM NO HDD Nvidia
$90.00
Rare WaterCooled HP Z800 Workstation Dual Xeon X5680 16GB RAM 120GB SSD Nvidia
$279.56