Kernel panic with Packstack and AMD Ryzen on instance boot

I configured my AMD Ryzen box as a Packstack deployment today and ran into a perplexing problem. When I’d try to boot any instance – cirros, CentOS, doesn’t matter – I’d see lines like this in the log:

[    0.329569] ---[ end trace 8761dba085238f6f ]---
[    0.330876] Kernel panic - not syncing: Attempted to kill the idle task!
[    0.332674] ---[ end Kernel panic - not syncing: Attempted to kill the idle task!

The issue ended up being the CPU model being exposed to the VM via libvirt.

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