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[Bug 460042] [Virtualization:KVM] kernel: kvm: enabling virtualization on CPU1 failed
  • From: bugzilla_noreply@xxxxxxxxxx
  • Date: Sun, 4 Jan 2009 06:31:30 -0700 (MST)
  • Message-id: <20090104133130.65114CC7D4@xxxxxxxxxxxxxxxxxxxxxx>
https://bugzilla.novell.com/show_bug.cgi?id=460042

User agraf@xxxxxxxxxx added comment
https://bugzilla.novell.com/show_bug.cgi?id=460042#c7





--- Comment #7 from Alexander Graf <agraf@xxxxxxxxxx> 2009-01-04 06:31:26 MST
---
Now, that sounds bad. Could you please try to build a vanilla KVM version from
kvm.sourceforge.net and see if modprob'ing that fails after you used
VirtualBox?

Just to make sure I understand things correctly: Is the VirtualBox VM still
running when you start the KVM VM? That would definitely point at a bug in
VirtualBox.

To easily explain things:

There is a hardware register that has to be turned on for virtualization to be
used, which is called EFER.SVME. It commonly can only be set by one hypervisor.
Vanilla KVM sets this when kvm-amd is modprobe'd, whereas the SUSE version
you're using sets it when the first VM is created. This is to allow
automodprob'ing of the kernel module without breaking VirtualBox/VMware and the
like.

Now, if VirtualBox sets the register without using it, KVM can't run anymore.
If KVM sets it (by starting a VM) and VirtualBox doesn't care when you run that
VM, everything's fine.

Basically this means:

If you're running a VirtualBox VM with SVM support and try to run a KVM VM that
can not work.

If you're running a VirtualBox VM without hardware virtualization, try to start
KVM while it's running and starting the KVM VM fails, VirtualBox incorrectly
claimed the EFER.SVME register.

If you're done using VirtualBox, start a KVM VM and that fails, VirtualBox
didn't free the EFER.SVME register.

The same goes for KVM of course. If you can't run VirtualBox after you closed
the last KVM VM (with SUSE KVM), that's definitely a bug.

To narrow down the problem in order to tell Sun about it, it would be nice to
know where exactly the problem occurs. I might find some time to play around
with the different combinations next week, but if you're faster it'd be awesome
if you could pinpoint it.


PS: The "on demand SVME activation patches" for KVM are on their way upstream -
they just didn't make it yet because another huge patchset was touching the
same code pathes when I did that patch.


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