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Signed-off-by: Nikolaos Karaolidis <nick@karaolidis.com>

content/posts/nested-virtualization/index.md

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+title = "Pushing Nested Virtualization to the Limits"
+date = 2022-04-27T19:54:00Z
+draft = false
+summary = "Trying to install all versions of Windows inside nested VMs..."
+tags = ["Experiment", "Virtualization", "Linux", "Windows"]
+
+aliases = ['/nested-virtualization']
+
+[hero]
+src = "hero.jpg"
+caption = 'Photo by <a href="https://unsplash.com/@didsss">Didssph</a> via <a href="https://unsplash.com">Unsplash</a>'
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+
+I recently watched a video by SomeOrdinaryGamers in which he decided to install the first version of Windows and upgrade it all the way to Windows 10.
+
+{{< youtube id=KD3tuWy-z_w loading=lazy start=92 >}}
+
+Despite the video's thumbnail, I decided that it would a good idea to do something similar: Install all versions of Windows inside nested VMs.
+
+> [!warning] Disclaimer
+> Do not try this at home. Or do, I don't really care. Just be warned that it is a massive waste of time :upside_down_face:.
+
+Sadly, I didn't have access to my supercomputer with 1000s of CPU cores and Terabytes of RAM at the time, so my Legion 7 would have to do. Its specs are as follows:
+
+- AMD Ryzen 7 5800H (8 Cores, 16 Threads, Base 3.2GHz, Turbo 4.4GHz)
+- NVIDIA GeForce RTX 3070 Mobile
+- 32GB DDR4 3200MHz RAM
+- 2TB M.2 NVMe PCIe SSD
+
+About a month ago I completed a [single-GPU VFIO passthrough]({{% ref "/posts/vfio" %}}), which allowed me to have near-bare-metal performance on a Windows 10 VM running inside Arch Linux. This meant that my host was pretty much ready to go.
+
+![Host OS: Arch Linux](host.png)
+
+The plan was simple: Install virtualization software on every operating system and create the nested VMs. Easy, right? Well... The execution was a bit tougher.
+
+## First VM
+
+My first victim was my Windows 10 Gaming VM. If you want detailed instructions on how I created it, you can check out the post linked above.
+
+![First Virtual Machine: Windows 10](level-0.png)
+
+I originally tried going the Hyper-V route for my next VM but performance inside Windows 10 tanked significantly the moment I enabled it, forcing me to install VirtualBox.
+
+## Second VM
+
+After installing VirtualBox, I downloaded a [Windows 8.1 ISO](https://www.microsoft.com/en-us/software-download/windows8ISO) from Microsoft and created a new VM.
+
+![Second Virtual Machine Config](level-1-config.png)
+
+I gave this VM around half of the resources of Windows 10, making sure to also enable nested AMD-V. After a painfully nit-picky installation (thanks Microsoft), I was finally able to boot Windows 8.1.
+
+![Second Virtual Machine: Windows 8.1](level-1.png)
+
+General performance was OK-ish and the VM was definitely usable. However, networking was unfathomably slow, peaking at around 0.8MB/s.
+
+Luckily, VirtualBox provides easy folder sharing between hosts and guests, so all I had to do was download any needed files on Windows 10 and pass them through to Windows 8.1.
+
+After installing VirtualBox once again, it was time for the third VM.
+
+## Third VM
+
+This is where things started to get a bit annoying. As you might know, Microsoft has dropped support for Windows 7, so finding an ISO was a bit more difficult. Luckily, with a bit of google-fu, I found a website that hosted a direct download link.
+
+While configuring the VM, I noticed that I could no longer enable nested AMD-V. Uh-oh.
+
+![Third Virtual Machine Config](level-2-config.png)
+
+Staying optimistic, I pressed forward and started the Windows 7 installation. I quickly realized that this challenge was a lot harder than I originally expected.
+
+![Third Virtual Machine Config](level-2.png)
+
+The installation took a total of 4 painfully slow hours, ending with a blue screen of death right after the installer tried to reboot the VM. All hope was not yet lost though.
+
+I restarted the VM, and after a one-hour-long boot process (I am not joking), I was greeted with the Windows 7 desktop. Even though the VM booted, the user interface felt beyond sluggish, with every click taking several seconds to register, and animations tearing up the whole screen.
+
+However, this didn't stop me and my hubris. I installed VirtualBox again.
+
+## Fourth VM
+
+My next target was Windows XP. I deliberately skipped Vista because I was too scared of the performance impact it would have. After downloading a dodgy Windows XP ISO, I created a new VM inside VirtualBox.
+
+This is where I started to realize that my ~insanity~ experiment would soon come to an end. Almost all options, including multiple cores and hardware acceleration, were greyed-out.
+
+Despite that, I still tried to create a VM. After configuring the available options, I started the Windows XP installation. Sadly, after another hour, I was greeted with an error message saying that AMD-V was not available.
+
+![He's dead, Jim](game-over.png)
+
+## Conclusion
+
+In the end, I managed to create a measly 2 nested VMs before being stopped by VirtualBox limitations.
+
+I'm guessing that by using the more efficient KVM platform I would be able to nest at least 3, possibly 4 VMs. However, that is an experiment for another time.
+
+What did I learn from this experience? Absolutely nothing, other than that I am really good at finding ways to procrastinate.