Difference between revisions of "stoney cloud: Nested virtualization"
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You either have to reboot or <code>rmmod/modprobe</code> the corresponding module if no VM is running | You either have to reboot or <code>rmmod/modprobe</code> the corresponding module if no VM is running | ||
| + | == VM configuration == | ||
| + | |||
| + | The following is largely untested, therefore this is more an instruction on how to figure out what the correct setting is. | ||
| + | |||
| + | First try to start any VM and execute the following to see whether virtualization is available '''in the guest''': | ||
| + | |||
| + | <source lang='bash'> | ||
| + | grep vmx /proc/cpuinfo | ||
| + | </source> | ||
| + | |||
| + | If there is support, the output should be something like this: | ||
| + | |||
| + | <pre> | ||
| + | flags : [...] vmx [...] | ||
| + | </pre> | ||
| + | |||
| + | If it does not get enabled automatically by libvirt as soon as the hypervisor supports nested virtualization (it should, though), you have to change to XML description of the VM. To that end, use <code>virsh edit</code> on the node after having it defined it and replace the lines: | ||
| + | |||
| + | <source lang='xml'> | ||
| + | <cpu mode='host-model'> | ||
| + | <model fallback='allow'/> | ||
| + | </cpu> | ||
| + | </source> | ||
| + | |||
| + | with | ||
| + | |||
| + | <source lang='xml'> | ||
| + | <cpu mode='host-model'> | ||
| + | <model fallback='allow'/> | ||
| + | <feature policy='require' name='vmx'/> | ||
| + | </cpu> | ||
| + | </source> | ||
[[Category:stoney cloud]][[Category:Installation]] | [[Category:stoney cloud]][[Category:Installation]] | ||
Revision as of 14:24, 20 December 2013
Abstract
This document describes how to set up nested virtualization on a default installation (until it gets enabled by default).
Nested virtualization permits to start another hypervisor (in our case KVM) inside a virtual machine.
With the current version of Qemu/KVM you can expect a performance of about 25% of the host performance (concerning CPU and Memory access) in a guest within a guest (L2). In the future Qemu/KVM should support Intels Virtual EPT which should give 80% of the host performance for L2.
See:
- http://events.linuxfoundation.org/sites/events/files/cojp13_nakajima.pdf
- https://docs.google.com/file/d/0BzyAwvVlQckedmpobUY1Sm0zNWc/edit
For Intel CPUs we are going to enable Shadow VMCS which requires a sufficiently new CPU, otherwise it gets ignored. This should give some performance increase, disable it if it causes problems.
Setup
Login as root, then execute the following:
cat > /etc/modprobe.d/nested-virtualization.conf << EOF options kvm-intel nested=Y enable_shadow_vmcs=Y options kvm-amd nested=Y EOF
You either have to reboot or rmmod/modprobe the corresponding module if no VM is running
VM configuration
The following is largely untested, therefore this is more an instruction on how to figure out what the correct setting is.
First try to start any VM and execute the following to see whether virtualization is available in the guest:
grep vmx /proc/cpuinfo
If there is support, the output should be something like this:
flags : [...] vmx [...]
If it does not get enabled automatically by libvirt as soon as the hypervisor supports nested virtualization (it should, though), you have to change to XML description of the VM. To that end, use virsh edit on the node after having it defined it and replace the lines:
<cpu mode='host-model'> <model fallback='allow'/> </cpu>
with
<cpu mode='host-model'> <model fallback='allow'/> <feature policy='require' name='vmx'/> </cpu>
