I've installed Manjaro in a guest VM on an Ubuntu 18.10 host, but I cannot make the guest additions work in my Manjaro guest.
I've installed kernel 5.1.1-2 in Manjaro, and the output of uname -r is:
5.1.1-2-MANJARO
Then, I tried installing virtualbox-guest-utils, and when I do that it gives me the option to choose which provider I want to use:
And here, I enter 8 to use linux51-virtualbox-guest-modules, but when I reboot my machine, nothing changes (I expect the display size to be adjusted to the window size etc., but nothing!)
Is it possible I'm missing something on my Ubuntu host? I have a Windows 10 VM and guest additions work fine in that.

VMSVGAtoVBoxVGA. I would answer the question here myself, but I don't think I'm able to do it :(