Difference between revisions of "stoney cloud: Nested virtualization"
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* https://docs.google.com/file/d/0BzyAwvVlQckedmpobUY1Sm0zNWc/edit | * https://docs.google.com/file/d/0BzyAwvVlQckedmpobUY1Sm0zNWc/edit | ||
| − | For Intel CPUs we are going to enable [http://www.spinics.net/lists/kvm/msg87634.html Shadow VMCS] which requires a sufficiently new CPU, otherwise it gets ignored. | + | For Intel CPUs we are going to enable [http://www.spinics.net/lists/kvm/msg87634.html 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 == | == Setup == | ||
| + | === Intel === | ||
| + | Login as root, then execute the following: | ||
| + | <source lang='bash'> | ||
| + | cat > /etc/modprobe.d/nested-virtualization.conf << EOF | ||
| + | options kvm-intel nested=Y enable_shadow_vmcs=Y | ||
| + | EOF | ||
| + | </source> | ||
| − | + | You either have to reboot or <code>rmmod/modprobe</code> the corresponding module if no VM is running. For example: | |
| + | rmmod kvm_intel | ||
| + | modprobe kvm_intel | ||
| + | === AMD === | ||
| + | Login as root, then execute the following: | ||
<source lang='bash'> | <source lang='bash'> | ||
cat > /etc/modprobe.d/nested-virtualization.conf << EOF | cat > /etc/modprobe.d/nested-virtualization.conf << EOF | ||
| − | |||
options kvm-amd nested=Y | options kvm-amd nested=Y | ||
EOF | EOF | ||
| + | </source> | ||
| + | |||
| + | You either have to reboot or <code>rmmod/modprobe</code> the corresponding module if no VM is running. For example: | ||
| + | rmmod kvm_amd | ||
| + | modprobe kvm_amd | ||
| + | |||
| + | == VM configuration == | ||
| + | |||
| + | The following is largely untested, therefore this is more an instruction on how to figure out what the correct setting is. (hint: remove this line and update the configuration below if you have figured it out) | ||
| + | |||
| + | First try to start any VM and execute the following '''inside a Linux guest''' to see whether virtualization is available: | ||
| + | |||
| + | <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> | </source> | ||
[[Category:stoney cloud]][[Category:Installation]] | [[Category:stoney cloud]][[Category:Installation]] | ||
Latest revision as of 14:57, 24 December 2013
Contents
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
Intel
Login as root, then execute the following:
cat > /etc/modprobe.d/nested-virtualization.conf << EOF options kvm-intel nested=Y enable_shadow_vmcs=Y EOF
You either have to reboot or rmmod/modprobe the corresponding module if no VM is running. For example:
rmmod kvm_intel modprobe kvm_intel
AMD
Login as root, then execute the following:
cat > /etc/modprobe.d/nested-virtualization.conf << EOF options kvm-amd nested=Y EOF
You either have to reboot or rmmod/modprobe the corresponding module if no VM is running. For example:
rmmod kvm_amd modprobe kvm_amd
VM configuration
The following is largely untested, therefore this is more an instruction on how to figure out what the correct setting is. (hint: remove this line and update the configuration below if you have figured it out)
First try to start any VM and execute the following inside a Linux guest to see whether virtualization is available:
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>
