I'm trying to properly install virtualbox guest additions to a guest linux Debian virtual machine. The problem is that video performance, at 1920x1080 is crap. The host is a macOS core i5 with a radeon R9 M395.

I've installed all virtualbox-guest packages: virtualbox-guest-x11 virtualbox-guest-dkms virtualbox-guest-addittions

After looking inside /var/log/Xorg.0.log it seems that vboxvideo module is not loading.

... [ 15.387] (II) LoadModule: "vboxvideo" [ 15.388] (WW) Warning, couldn't open module vboxvideo [ 15.388] (II) UnloadModule: "vboxvideo" [ 15.388] (II) Unloading vboxvideo [ 15.388] (EE) Failed to load module "vboxvideo" (module does not exist, 0) ...

` $ dkms stat virtualbox-guest, 5.1.12, 4.8.0-2-amd64, x86_64: installed

$ uname -r 4.8.0-2-amd64

$ lsmod| grep vbox vboxsf 49152 0 vboxvideo 49152 2 vboxguest 282624 6 vboxsf,vboxvideo ttm 98304 1 vboxvideo drm_kms_helper 155648 1 vboxvideo drm 360448 5 vboxvideo,ttm,drm_kms_helper `

What's happening?

Where shall be located vboxvideo module? What is the filename?

Where shall I look next?