Today, I encountered the same issue. The error occurs due to a conflict between VirtualBox and KVM (a kernel module used for virtualization on Linux). VirtualBox requires exclusive access to the processor’s VMX root mode, but KVM is already using this mode.
Solution:
Temporary Fix:
Disable the KVM Module (temporary solution):
Check if the KVM module is loaded and disable it for the current session:
lsmod | grep kvm
If the output shows kvm_intel or kvm_amd, unload them:
This will temporarily disable KVM until the next reboot.
Permanent Fix:
Prevent KVM from Loading at Boot Using nano (permanent solution):
To ensure the KVM modules don’t load again after a reboot, manually create a blacklist configuration file:
Open the blacklist file in a text editor like nano:
pacman -Syu will, however, upgrade again to 6.12 unless you exclude the packages from upgradeing, see: Skip package from being upgraded.
So either refrain from the urge to click that “upgrade system” button of yours or accept holding back individual packages in arch, which is considered unsupported or at least discourgaed.
For the kernel packages this is probably not too disrupting as it would be for libraries and other applications. That is, if you haven’t done stuff running 6.12 that now requires 6.12 features/changes, probably filesystem related.
Linux Guest Additions: Introduce initial support for kernel 6.12 (NOTE: In kernel 6.12, KVM initializes virtualization on module loading by default. This prevents VirtualBox VMs from starting. In order to avoid this, either add “kvm.enable_virt_at_load=0” parameter into kernel command line or unload corresponding kvm_XXX module)