Nested virtualization/AMD-V in the guest: Success stories (and failures)

[socratis]

I was wondering how virtual box VM inside ESXi VM (ESXi v6.5) was working fine when virtual box version was 5.1.30

I was doing nested virtualization for years. The question is "what" nested virtualization.

Because if you're talking about running a FreeDOS VM, it was working. I'm not sure if it's going to work anymore, now that "raw" mode has been deprecated and VT-x is required even for smallest of the VMs...

[HulkySulky]

Here's my (failure) story. Basically (at least with Debian 10) it's not working. It's on an Intel laptop, not AMD, but since 6.1 Intel's CPU are supposed to be supported by VirtualBox for nested virtualization.

Physical Host :
- Processor : Intel Core i7-10510U @1.80GHz (1 proc, 4 cores, 8 threads)
- RAM : 16GB
- OS : Debian 10.2 (latest)
- VirtualBox 6.1.2 r135662 (latest) with extension pack installed

Guest :
- 4 CPU
- 10GB RAM
- OS : Debian 10
- Guest Additions installed
- VirtualBox 6.1.2 r135662 with nested VT-x/AMD-V enabled and extension pack installed

Nested Guest :
- 2 CPU
- 2GB RAM

I tried a fresh installation of Debian 10 into the nested guest. At first, the installation process seems to start (I get to the screen where you have to choose the installation type), but right after that it freezes both the guest and the nested guest. In the physical host I can see 100% workload on half of the processors. I waited for 10 minutes, then I killed the guest.

Second try : I migrated a Win7 VM into the guest. Same result, after starting the nested guest (Win7), Windows starts but doesn't reach the login screen. Soon both the nested guest (Win7) and the guest (Debian 10) are frozen, with 100% workload on half of the physical host's processors. Waited for 10 minutes, then killed the guest.