140 lines
3.7 KiB
ReStructuredText
140 lines
3.7 KiB
ReStructuredText
=======================================================
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Configure DevStack with KVM-based Nested Virtualization
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=======================================================
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When using virtualization technologies like KVM, one can take advantage
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of "Nested VMX" (i.e. the ability to run KVM on KVM) so that the VMs in
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cloud (Nova guests) can run relatively faster than with plain QEMU
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emulation.
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Kernels shipped with Linux distributions doesn't have this enabled by
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default. This guide outlines the configuration details to enable nested
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virtualization in KVM-based environments. And how to setup DevStack
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(that'll run in a VM) to take advantage of this.
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Nested Virtualization Configuration
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===================================
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Configure Nested KVM for Intel-based Machines
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---------------------------------------------
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Procedure to enable nested KVM virtualization on Intel-based machines.
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Check if the nested KVM Kernel parameter is enabled:
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::
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cat /sys/module/kvm_intel/parameters/nested
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N
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Temporarily remove the KVM intel Kernel module, enable nested
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virtualization to be persistent across reboots and add the Kernel
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module back:
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::
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sudo rmmod kvm-intel
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sudo sh -c "echo 'options kvm-intel nested=y' >> /etc/modprobe.d/dist.conf"
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sudo modprobe kvm-intel
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Ensure the Nested KVM Kernel module parameter for Intel is enabled on
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the host:
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::
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cat /sys/module/kvm_intel/parameters/nested
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Y
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modinfo kvm_intel | grep nested
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parm: nested:bool
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Start your VM, now it should have KVM capabilities -- you can verify
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that by ensuring ``/dev/kvm`` character device is present.
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Configure Nested KVM for AMD-based Machines
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-------------------------------------------
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Procedure to enable nested KVM virtualization on AMD-based machines.
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Check if the nested KVM Kernel parameter is enabled:
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::
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cat /sys/module/kvm_amd/parameters/nested
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0
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Temporarily remove the KVM AMD Kernel module, enable nested
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virtualization to be persistent across reboots and add the Kernel module
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back:
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::
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sudo rmmod kvm-amd
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sudo sh -c "echo 'options kvm-amd nested=1' >> /etc/modprobe.d/dist.conf"
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sudo modprobe kvm-amd
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Ensure the Nested KVM Kernel module parameter for AMD is enabled on the
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host:
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::
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cat /sys/module/kvm_amd/parameters/nested
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1
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modinfo kvm_amd | grep -i nested
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parm: nested:int
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To make the above value persistent across reboots, add an entry in
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/etc/modprobe.d/dist.conf so it looks as below::
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cat /etc/modprobe.d/dist.conf
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options kvm-amd nested=y
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Expose Virtualization Extensions to DevStack VM
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-----------------------------------------------
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Edit the VM's libvirt XML configuration via ``virsh`` utility:
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::
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sudo virsh edit devstack-vm
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Add the below snippet to expose the host CPU features to the VM:
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::
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<cpu mode='host-passthrough'>
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</cpu>
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Ensure DevStack VM is Using KVM
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-------------------------------
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Before invoking ``stack.sh`` in the VM, ensure that KVM is enabled. This
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can be verified by checking for the presence of the file ``/dev/kvm`` in
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your VM. If it is present, DevStack will default to using the config
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attribute ``virt_type = kvm`` in ``/etc/nova.conf``; otherwise, it'll fall
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back to ``virt_type=qemu``, i.e. plain QEMU emulation.
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Optionally, to explicitly set the type of virtualization, to KVM, by the
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libvirt driver in nova, the below config attribute can be used in
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DevStack's ``local.conf``:
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::
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LIBVIRT_TYPE=kvm
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Once DevStack is configured successfully, verify if the Nova instances
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are using KVM by noticing the QEMU CLI invoked by Nova is using the
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parameter ``accel=kvm``, e.g.:
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::
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ps -ef | grep -i qemu
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root 29773 1 0 11:24 ? 00:00:00 /usr/bin/qemu-system-x86_64 -machine accel=kvm [. . .]
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