How to crash the server playing with VM CPU configuration... is it normal?

[mmenaz]

Hi, I've a vm (Kubuntu 19.04) that I use to test Freecad and that I turn on when needed. I've no need of "mitigations" about CPU flaws or whatever, I just need more performance I can.
In the vm I've disabled all CPU flags (-md-clear;-pcid;-spec-ctrl;-ssbd;-ibpb;-virt-ssbd;-amd-ssbd;-amd-no-ssb), and my home server has AMD cpu FX-6300 Six-Core Processor, pve no-subscription 6.1-5/9bf06119 (running kernel: 5.3.13-1-pve).
So far so good. To have even more power in the VM I've had the idea to change the CPU type from 'kvm64' to 'host'.
Then I've turned on the VM, everything went fine to the login then THE PROXMOX SERVER crashed and rebooted!
I would love to know if is a bug, if I've done something wrong, or what else. I've no tried again since then, has not been a peasant experience.

 

[Stefan_R]

Setting the CPU type to host exposes *all* features to the VM. This can cause instability, although a full crash is still not good ofc.

Try setting up kdump to get a dmesg log when it crashes the next time.