It's really funny. I have searched by google and found many issues said that kvm and VB cannot running at the same machine. On one discussing at VB's forum, the answer is "INPOSSIBLE".
But I have two machines now running both of them. The first machine is use AMD 7960 CPU and the second AMD 945. On the first machine, the host is Ubuntu server 10.04, upgraded from 9.10. and it have 5 kvm guest running, 3 ubuntu servers, 2 windows servers. AND, it have a VirtualBox guest running also. I used one VirtualBox guest because it hve better support for USB devices. The second machine have similar situation. Both machines have been running well for almost a year!
Last month, I bought a new machine. This time, I have a Intel i7 930 CPU. But this time when I try to running both VB and KVM, problem happened as many of people have seen. When I trying to start a VB guest, I got below error:
Error: failed to start machine. Error message: VirtualBox can't operate in VMX root mode. Please disable the KVM kernel extension, recompile your kernel and reboot (VERR_VMX_IN_VMX_ROOT_MODE)
If if remove the kvm_intel module by below command or blacklisted it as boot:
# modprobe -r kvm_intel
The VB guest can start but KVM guest will not!
Someone said to disable the VM support at bios maybe will help. I will try it later. I will let you know the result.
Do you have any lights?