Comment 9 for bug 1720397

I was testing the fix from a ppa:

With debug enabled this looks much better now.

Install:

Setting up qemu-system-common (1:2.10+dfsg-0ubuntu3~ppa2) ...
(deb-systemd-helper DEBUG) is purge = no
(deb-systemd-helper DEBUG) action = unmask, scriptname = qemu-kvm.service, service_path = /lib/systemd/system/qemu-kvm.service
(deb-systemd-helper DEBUG) rmdir_if_empty /var/lib/systemd/deb-systemd-helper-masked
(deb-systemd-helper DEBUG) rmdir(/var/lib/systemd/deb-systemd-helper-masked) failed (No such file or directory)
(deb-systemd-helper DEBUG) is purge = no
(deb-systemd-helper DEBUG) action = was-enabled, scriptname = qemu-kvm.service, service_path = /lib/systemd/system/qemu-kvm.service
(deb-systemd-helper DEBUG) Reading state file /var/lib/systemd/deb-systemd-helper-enabled/qemu-kvm.service.dsh-also
(deb-systemd-helper DEBUG) Contents: $VAR1 = [];

(deb-systemd-helper DEBUG) All links present, considering qemu-kvm.service was-enabled.
(deb-systemd-helper DEBUG) is purge = no
(deb-systemd-helper DEBUG) action = enable, scriptname = qemu-kvm.service, service_path = /lib/systemd/system/qemu-kvm.service
(deb-systemd-helper DEBUG) Using systemctl preset to enable qemu-kvm.service
Created symlink /etc/systemd/system/multi-user.target.wants/qemu-kvm.service → /lib/systemd/system/qemu-kvm.service.
(deb-systemd-helper DEBUG) Renaming temp file /var/lib/systemd/deb-systemd-helper-enabled/.stateJvURx.tmp to state file /var/lib/systemd/deb-systemd-helper-enabled/qemu-kvm.service.dsh-also
● qemu-kvm.service - QEMU KVM preparation - module, ksm, hugepages
   Loaded: loaded (/lib/systemd/system/qemu-kvm.service; enabled; vendor preset: enabled)
   Active: active (exited) since Mon 2017-10-16 14:27:33 UTC; 1s ago
  Process: 4559 ExecStart=/usr/share/qemu/init/qemu-kvm-init start (code=exited, status=0/SUCCESS)
 Main PID: 4559 (code=exited, status=0/SUCCESS)
      CPU: 4ms

Oct 16 14:27:33 artful-test-qemukvm systemd[1]: Starting QEMU KVM preparation - module, ksm, hugepages...
Oct 16 14:27:33 artful-test-qemukvm systemd[1]: Started QEMU KVM preparation - module, ksm, hugepages.

More critical - upgrade on a system that was formerly in the broken state (all since zesty and artful so far).

[...]
Setting up qemu-system-common (1:2.10+dfsg-0ubuntu2) ...
● qemu-kvm.service - QEMU KVM preparation - module, ksm, hugepages
   Loaded: loaded (/lib/systemd/system/qemu-kvm.service; disabled; vendor preset: enabled)
   Active: inactive (dead)
# _DEB_SYSTEMD_HELPER_DEBUG=1 apt install -y qemu-system-common; systemctl status qemu-kvmReading package lists... Done
Building dependency tree
Reading state information... Done
The following package was automatically installed and is no longer required:
  libfreetype6
Use 'apt autoremove' to remove it.
The following additional packages will be installed:
  qemu-block-extra
The following packages will be upgraded:
  qemu-block-extra qemu-system-common
2 upgraded, 0 newly installed, 0 to remove and 4 not upgraded.
Need to get 441 kB of archives.
After this operation, 2048 B of additional disk space will be used.
Get:1 http://ppa.launchpad.net/ci-train-ppa-service/2992/ubuntu artful/main amd64 qemu-system-common amd64 1:2.10+dfsg-0ubuntu3~ppa2 [401 kB]
Get:2 http://ppa.launchpad.net/ci-train-ppa-service/2992/ubuntu artful/main amd64 qemu-block-extra amd64 1:2.10+dfsg-0ubuntu3~ppa2 [40.0 kB]
Fetched 441 kB in 1s (342 kB/s)
(Reading database ... 26809 files and directories currently installed.)
Preparing to unpack .../qemu-system-common_1%3a2.10+dfsg-0ubuntu3~ppa2_amd64.deb ...
Unpacking qemu-system-common (1:2.10+dfsg-0ubuntu3~ppa2) over (1:2.10+dfsg-0ubuntu2) ...
Preparing to unpack .../qemu-block-extra_1%3a2.10+dfsg-0ubuntu3~ppa2_amd64.deb ...
Unpacking qemu-block-extra:amd64 (1:2.10+dfsg-0ubuntu3~ppa2) over (1:2.10+dfsg-0ubuntu2) ...
Setting up qemu-block-extra:amd64 (1:2.10+dfsg-0ubuntu3~ppa2) ...
Processing triggers for man-db (2.7.6.1-2) ...
Setting up qemu-system-common (1:2.10+dfsg-0ubuntu3~ppa2) ...
(deb-systemd-helper DEBUG) is purge = no
(deb-systemd-helper DEBUG) action = unmask, scriptname = qemu-kvm.service, service_path = /lib/systemd/system/qemu-kvm.service
(deb-systemd-helper DEBUG) rmdir_if_empty /var/lib/systemd/deb-systemd-helper-masked
(deb-systemd-helper DEBUG) rmdir(/var/lib/systemd/deb-systemd-helper-masked) failed (No such file or directory)
(deb-systemd-helper DEBUG) is purge = no
(deb-systemd-helper DEBUG) action = was-enabled, scriptname = qemu-kvm.service, service_path = /lib/systemd/system/qemu-kvm.service
(deb-systemd-helper DEBUG) Reading state file /var/lib/systemd/deb-systemd-helper-enabled/qemu-kvm.service.dsh-also
(deb-systemd-helper DEBUG) Contents: $VAR1 = [];

(deb-systemd-helper DEBUG) All links present, considering qemu-kvm.service was-enabled.
(deb-systemd-helper DEBUG) is purge = no
(deb-systemd-helper DEBUG) action = enable, scriptname = qemu-kvm.service, service_path = /lib/systemd/system/qemu-kvm.service
(deb-systemd-helper DEBUG) Using systemctl preset to enable qemu-kvm.service
Created symlink /etc/systemd/system/multi-user.target.wants/qemu-kvm.service → /lib/systemd/system/qemu-kvm.service.
(deb-systemd-helper DEBUG) Renaming temp file /var/lib/systemd/deb-systemd-helper-enabled/.statesHxaw.tmp to state file /var/lib/systemd/deb-systemd-helper-enabled/qemu-kvm.service.dsh-also
● qemu-kvm.service - QEMU KVM preparation - module, ksm, hugepages
   Loaded: loaded (/lib/systemd/system/qemu-kvm.service; enabled; vendor preset: enabled)
   Active: active (exited) since Mon 2017-10-16 14:31:24 UTC; 1s ago
  Process: 6891 ExecStart=/usr/share/qemu/init/qemu-kvm-init start (code=exited, status=0/SUCCESS)
 Main PID: 6891 (code=exited, status=0/SUCCESS)
      CPU: 3ms

Oct 16 14:31:24 artful-test-qemukvm systemd[1]: Starting QEMU KVM preparation - module, ksm, hugepages...
Oct 16 14:31:24 artful-test-qemukvm systemd[1]: Started QEMU KVM preparation - module, ksm, hugepages.

Starting as well as it should.
Finally if one masked the service is shall stay masked and that worked as well.