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.
Gigabyte Aorus Ultra Durable B550 AORUS ELITE AX V2 Desktop Motherboard
$29.94
ASRock Z170M-ITX/ac LGA 1151 Intel Z170 HDMI USB 3.0 Mini ITX Intel Motherboard
$49.99
ASRock B550M Pro SE AM4 DDR4 SATA 6Gb/s 1 PCIe 4.0 x16 Micro ATX Motherboard
$84.99
MSI H81M-P33 Desktop Motherboard Intel MicroATX Socket LGA1150 USB 3.0 W/IO
$26.99
Gigabyte GA-Q170M-D3H-GSM LGA1151 DDR4 Desktop Motherboard (No I/O Plate)
$39.99
Asus Prime H310M-A R2.0 Intel LGA 1151 DDR4 Desktop Motherboard
$54.99
Asus H81M-C Intel LGA1150 DDR3 Desktop Motherboard MicroATX Socket H3
$23.99
Gigabyte GA-Q170M-MK LGA 1151 DDR4 Desktop Motherboard W/ IO
$40.95
MSI PRO B650-P WiFi AMD AM5 DDR5 WiFi 6E ProSeries Motherboard
$107.30
Gigabyte GA-Q170M-D3H-GSM LGA1151 DDR4 Desktop Motherboard with I/O Plate
$49.99