KVM-QEMU and Virtualbox - concurrent use of svm not possible

[ipic]

I have been using Virtualbox for several years now. I would like to move to KVM/QEMU. I am new to this, so apologies if this is a dumb topic or has been covered before.

There is a very old internet article about KVM and Virtualbox not co-existing due to kernel module clashes. However, in articles that talk about migrating Virtualbox to KVM there are also articles that say that the two can co-exist. Ideally I would like to convert one of my VMs at a time (I have four on the same machine), so this would be useful.

I followed the Gentoo wiki article https://wiki.gentoo.org/wiki/QEMU

I installed app-emulation/virt-manager, added my user to groups kvm, quem and libvirt, edited /etc/libvirt/libvirtd.conf as suggested, and started up /etc/init.d/libvirtd

In dmesg I then saw:

[dimko]

I have been ironic, but i did run ESXI inside of KVM.

And to be less ironic, unload drivers from virtual box, try kvm again. If works - then incompatible. If not, you have not dug deep enough. You have not made your kvm workable.

try "qemu-system-x86_64 -enable-kvm", if window pops up under Xorg, and fails to load - you are on right path. Probably your install is viable and CPU assisted virtualisation works.
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Just a user.

[NeddySeagoon]

ipic,

Works for me with both installed.
I have not run them both concurrently but I have both installed.

I use KVM/QEMU for something I want to keep around and Virtualbox for VMs that I intend to throw away, except they are mostly still around too. :)
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Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.

[ipic]

[Zucca]

This would explain why I cannot setup a vbox VM via virt-manager when I alrady have qemu/kvm VMs running...
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..: Zucca :..

[Hu]

If I recall correctly, when kvm was much younger, the incompatibility was more severe. I seem to recall claims that the hardware tracking of virtualization state had no inherent locking, and trying to run both kvm and virtualbox at the same time would cause a fatal exception on the host. That has long since been improved, to produce the situation shown here. You can't use them in parallel, but you can't break your system by trying to use them in parallel.

[Zucca]

A quick chat on IRC with a guy who's managing remote vms by using virt-manager confirmed that it's technically impossible to run the two simultaneously.

I guess it would need a kernel level modification/patch to be able to share the resource with more than two kvm hypervisors.

Someone else with more such low level knowledge can correct me if I'm wrong.
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..: Zucca :..

[Hu]

That sounds right. The hardware cannot handle being shared, so you need the two software components that want to use the hardware to cooperatively share the hardware, such as by having one ask the other to relinquish it. I could also see an argument that this is solving the wrong problem, and that the right solution is to get all the userspace frontends to standardize on a single kernel module that operates the virtualization hardware, so that no hand-off is needed because the hardware is always managed by KVM, regardless of whether you use Qemu or VirtualBox for the user process portion.

[solamour]

As for my case (https://forums.gentoo.org/viewtopic-t-1170571.html), VirtualBox VM doesn't start if I have CONFIG_KVM (and host of related configs) in the kernel. If I remove CONFIG_KVM, VirtualBox VM starts just fine.

Curious to know how others are able to run VirtualBox and KVM, not simultaneously, but one at a time.
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sol