Host system freezes as soon as the mouse pointer enters the VM on nVidia

[Luca Carlon]

Host system freezes immediately when mouse pointer enters the VM when running on nVidia with proprietary drivers. I tried to disable nVidia and run on Intel HD and the issue is not reproducible. The rest of the system is perfectly stable when running on nVidia. These are two logs of Virtualbox with different graphics controllers:

​https://pastebin.com/azj2dG3v ​https://pastebin.com/uCcQ45jL

After the mouse pointer enters the VM, the host freezes, so I cannot control the system anymore, I can only send sysrq and reboot. If I check kernel messages after the boot, this is what I found at the end of the previous session:

​https://pastebin.com/n83NqFhA

I do not know where the issue comes from, so I tried to report the issue also to nVidia here:

​https://devtalk.nvidia.com/default/topic/1056067/linux/virtualbox-freezes-my-system-when-on-nvidia-but-not-when-on-intel-hd/

but I thought I could also report to Virtualbox and see if together we can find a fix.

Host system is Kubuntu 19.04. Guest system I tried are KDE Neon and Kubuntu 19.04. I tried with official VirtualBox 6.0.8.

[Socratis]

Hello Luca (luc4),

I think it might be wiser to include logs and information here, locally; inline if they're small enough, as attachments otherwise.

[Luca Carlon]

VirtualBox log 1.

[Luca Carlon]

VirtualBox log 2.

[Luca Carlon]

Kernel log.

[Luca Carlon]

The problem seems to be related to a bug in kwin with triple-buffering. Disabling triple-buffering fixes the problem. The thread in the nVidia forum explains this better. I think this can be closed: doesn't seem to be related to virtualbox and it seems the fix is working properly.