Nested virtualization does not work with pve-5.4 kernel and AMD ryzen

TLTR: When you have an AMD Ryzen CPU and want to use any nested virtualization (nonfancy, just packer builds with Virtualbox) it will freeze about 5-10 seconds after starting the VM. To fix this issue, you need to upgrade your PVE kernel to 5.11.

My setup:
- Proxmox 6 latest patch version pve-manager/6.4-4/337d6701
- CPU AMD Ryzen 9 5950X 16-Core Processor
- NVMe drives / raid (if that can make any difference to this setup)

What i do:
Runing a Debian-buster VM with host type CPU, enabled nested virtualization (
Inside that VM I run packer based builds, more specifically
  • virtualbox 6.1 (latest)
  • packer 1.7.2 (latest)
Is used to build Debian-buster VMs. So during the build, a Debian buster VM should be provisioning via Virtualbox.

The nested VM started by VirtualBox will randomly freeze in about 10 seconds after booting the VM prior to any installation.

Upgrade your PVE kernel to 5.11 using

apt-get install pve-kernel-5.11

Hint: be aware, if you virtualize FreeBSD boxes, there is an issue when using cpu: host
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