Nova allows a variety of ways in which CPUs can be configured for
virtual machines. However, there had been a flurry of CPU hardware
flaws this year, and it is becoming increasingly difficult to choose an
optimal CPU configuration. This talk aims to provide some clarity
around this.
To that end, we'll start from the ground up by looking at QEMU (the open
source machine emulator and virtualizer) and the CPU configuration
interfaces it offers. Building on that, we will see how the libvirt
project uses the said interfaces to provide convenient APIs for
applications like OpenStack Nova. And, in turn, how Nova uses these
libvirt APIs to provide distinct CPU configuration modes for different
use cases.
We will also consider critical needs such as the ability to live migrate
a VM across hosts with diverse set of CPUs; or the flexibility to add or
remove specific CPU features from a given guest CPU model -- to mitigate
various hardware CPU flaws. We will tie all this together with some
real-world examples.
