Just a heads up for anyone running into problems with Virtualbox 5.2.22 direct from Oracle repos and being unable to get rid of Software Rendering in Mint 19 or 19.1 Beta Cinnamon edition guests even with Guest Additions installed and up to date.
The 5.2.22 Guest Additions are buggy and disable 3D acceleration across the board.
Solution 1 - downgrade to Virtualbox 5.2.20 - get the deb here - https://www.virtualbox.org/wiki/Download_Old_Builds_5_2
Use
apt deb
or sudo dpkg -i
to install in the terminal as Gdebi doesn't allow downgrades of installed applications. You'll need to reboot after downgrading. Install the 5.2.20 Guest Additions in the guest via Devices > Insert Guest Additions CD image. Solution 2 - Use a test build of the Guest Additions pending release of Virtualbox 5.2.24 - get the 5.2.23 Guest Additions iso here https://www.virtualbox.org/wiki/Testbuilds
In your guest operating system use the Devices menu > Optical Drives > Choose Disc Image to mount the alternative Guest Additions ISO. The installer should launch automatically.