virtualbox.org

VirtualBox 5.2.2 (Oracle version) on Xubuntu 16.04.3: as soon as the Linux guest starts using the "modeset" X driver (such as the Xubuntu 17.10 ISO does, no Guest Additions) the Preview mini display in the VirtualBox Manager GUI turns black.
For as far as I can remember this symptom started with VB 5.2.0, but I am sure I saw this with VB 5.2.1.
Please treat this as a minor complaint.

I know nada about the modeset X driver. Does it involve OpenGL? In which case it would be normal that the CPU has no access to the GPU framebuffer.

But, it has been ever thus, if a GPU renderer is involved. This is not new VirtualBox behaviour, though the use of a new renderer could be new guest behaviour.

Is this really that important? I've always seen the display preview as a pointless gimmick and a waste of CPU. Probably I'm missing something.

mpack wrote: I've always seen the display preview as a pointless gimmick and a waste of CPU.

+2!!!

Why +2? Because on OSX we have 2 (!) of these previews; one in VirtualBox Manager, and one in the Dock. Thankfully you can turn off the Dock one and saving *really whole of a lot* of CPU cycles. I guess you could select another idle VM in the VirtualBox Manager as well...

But, I digressed...

@mpack, @socratis: Thank you for the explanation.
I also regard this preview mini display as something dispensable. That is why I said "please treat this as a minor complaint".