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
DELL PowerEdge R730XD 24x 2.5" Server Dual 750W Dual Heatsink - BareBones TESTED
$269.99
HP ProLiant DL360 G9 Server 2x E5-2660v3 2.60Ghz 20-Core 96GB P440ar
$304.35
Dell PowerEdge R620 Server 2x E5-2660 v1 2.2GHz 16 Cores 256GB RAM 2x 300GB HDD
$79.19
Dell PowerEdge R730XD 28 Core Server 2X Xeon E5-2680 V4 H730 128GB RAM No HDD
$389.99
Dell PowerEdge R720XD Xeon E5-2680 V2 2.8GHz 20 Cores 256GB RAM 12x4TB
$510.00
HP ProLiant BL460c G9 (Gen9) 2x E5-2670V3 12 Core 3.1GHz No Ram or No Drives
$59.98
Dell PowerEdge R620 Server 2x E5-2650 V2 = 16 Cores H710P 128GB RAM 2x 600GB SAS
$274.99
HP Proliant DL360 Gen9 1x E5-2620 V3 2.40GHZ 32GB DDR4-1866MHZ 2x 500W PSU
$105.95