Libvirt kvm-steal-time disabler

Qemu allows disabling KVM steal time by passing a special -kvm-steal-time CPU flag. Libvirt does not recognize this flag, so there is no way to set it in the libvirt.

This library is meant to be used as LD_PRELOAD hook to libvirtd process to wrap the stdlib execve() function. It detects when libvirt tries to launch "qemu-system-*" process, and injects the cpu flag into it, effectively disabling steal time accounting for the virtual machine.

This is an alternative to patching libvirt/qemu/kernel.

How to use

1. Build it by running make
2. Put the resulting .so file into some directory.
3. Create a systemd drop-in file in the following directory: /etc/systemd/system/<the name of libvirt service>.d/injectflag.conf. You can find the name of the libvirt service by running systemctl | grep libvirt. In Debian, Ubuntu systems it is libvirtd.service.

The drop-in file contents:

[Service]
Environment=LD_PRELOAD=/<your>/<directory>/injectflag.so

4. Daemon reload and restart libvirtd:

systemctl daemon-reload
systemctl restart libvirtd

5. Try to start a virtual machine and look if the resulting qemu command line contains it: ps aux | grep qemu | grep steal-time. If its there, then you are good to go.