Add article: VirtualBox Black Screen on Threadripper (#1256)

Nested paging must be disabled on some Threadripper and Threadripper Pro
products in order for VirtualBox guests to display properly.

I compressed the larger screenshots with WebP, but left the smaller ones
as optimized PNG because the compression looks bad when they're scaled up.

content/virtualbox-threadripper.md

@@ -0,0 +1,54 @@
+---
+title: VirtualBox Black Screen on Threadripper Platforms (Solution)
+description: >
+  How to enable video output in VirtualBox guests on hosts using Threadripper or Threadripper Pro CPUs.
+keywords:
+  - VirtualBox
+  - Threadripper
+  - Threadripper Pro
+  - black screen
+  - blank screen
+  - no video
+  - virtual machine
+  - settings
+
+facebookImage: /_social/article
+twitterImage: /_social/article
+
+hidden: false
+section: software-troubleshooting
+tableOfContents: true
+---
+
+On some products using AMD Threadripper or Threadripper Pro processors, VirtualBox guests may display a blank screen as seen below:
+
+![VirtualBox guest showing a blank screen](/images/virtualbox-threadripper/virtual-machine-black-screen.webp)
+
+On systems affected with this issue, checking `VBox.log` while the virtual machine is running will show the following log line every second:
+
+```
+ERROR [COM]: aRC=VBOX_E_VM_ERROR (0x80bb0003) aIID={4680b2de-8690-11e9-b83d-5719e53cf1de} aComponent={DisplayWrap} aText={Could not take a screenshot (VERR_NOT_SUPPORTED)}, preserve=false aResultDetail=-37
+```
+
+Affected System76 models include:
+
+- Thelio Major R5
+- Thelio Mega R3
+
+## Solution: Disable Nested Paging
+
+In order to allow VirtualBox guests to properly show their displays, ensure the virtual machine is not running, then open the virtual machine's settings.
+
+![Virtual machine settings button](/images/virtualbox-threadripper/vm-settings-button.png)
+
+Navigate to the `System` page, then to the `Acceleration` tab.
+
+![Virtual machine System/Acceleration settings section](/images/virtualbox-threadripper/vm-system-acceleration-settings.png)
+
+Uncheck the checkbox labeled `Enable Nested Paging`.
+
+![VirtualBox nested paging setting](/images/virtualbox-threadripper/vm-disable-nested-paging.png)
+
+Select `OK` to save the settings, then start the virtual machine again. The display will output successfully.
+
+![VirtualBox guest showing a working screen](/images/virtualbox-threadripper/virtual-machine-working-screen.webp)