From 9debff637fb4fedde14d6e76789042fae7cec059 Mon Sep 17 00:00:00 2001
From: Joel Low <joel.low@supabase.io>
Date: Fri, 14 Aug 2026 15:46:27 +0800
Subject: [PATCH] feat: add guest-to-host time synchronisation

---
 ansible/files/phc2sys.service.j2     | 10 +++++
 ansible/tasks/setup-kvm-timesync.yml | 55 ++++++++++++++++++++++++++++
 ansible/tasks/setup-system.yml       |  6 +++
 3 files changed, 71 insertions(+)
 create mode 100644 ansible/files/phc2sys.service.j2
 create mode 100644 ansible/tasks/setup-kvm-timesync.yml

diff --git a/ansible/files/phc2sys.service.j2 b/ansible/files/phc2sys.service.j2
new file mode 100644
index 000000000..3e949d3a4
--- /dev/null
+++ b/ansible/files/phc2sys.service.j2
@@ -0,0 +1,10 @@
+[Unit]
+Description=Sync system clock to KVM PTP clock
+After=dev-ptp0.device
+
+[Service]
+ExecStart=/usr/sbin/phc2sys -s /dev/ptp0 -O 0 -m
+Restart=always
+
+[Install]
+WantedBy=multi-user.target
diff --git a/ansible/tasks/setup-kvm-timesync.yml b/ansible/tasks/setup-kvm-timesync.yml
new file mode 100644
index 000000000..243c2a33d
--- /dev/null
+++ b/ansible/tasks/setup-kvm-timesync.yml
@@ -0,0 +1,55 @@
+# Replace systemd-timesyncd with phc2sys which uses the KVM-exposed PTP timesource. Don't run NTP syncs within the VM
+# since that drifts more, and requires network access. phc2sys doesn't require any network access.
+- name: phc2sys - install
+  ansible.builtin.apt:
+    pkg:
+      - linuxptp
+
+- name: phc2sys - create service file
+  ansible.builtin.template:
+    src: files/phc2sys.service.j2
+    dest: /etc/systemd/system/phc2sys.service
+
+- name: phc2sys - enable service
+  ansible.builtin.systemd_service:
+    daemon_reload: true
+    enabled: true
+    name: 'phc2sys'
+    state: 'stopped'
+
+- name: phc2sys - remove systemd-timesyncd
+  ansible.builtin.apt:
+    pkg:
+      - systemd-timesyncd
+    purge: true
+    state: absent
+  when:
+    - ansible_distribution == "Ubuntu" and ansible_distribution_version == "24.04"
+
+- name: ptp_kvm.ko - enable
+  ansible.builtin.copy:
+    content: |
+      ptp_kvm
+    dest: /etc/modules-load.d/ptp_kvm.conf
+
+# On Ubuntu 24.04, ptp_kvm.ko is installed with the much larger linux-modules-extra package until after Kernel 6.8.
+# https://bugs.launchpad.net/ubuntu/+source/linux-gcp/+bug/2110241
+#
+# I didn't bisect every version because rebuilding a test image takes ~45 minutes. We can remove when we've fully
+# migrated to Ubuntu 26.04.
+- name: Upgrade running kernel
+  ansible.builtin.apt:
+    pkg:
+      - linux-virtual-7.0
+  when:
+    - ansible_distribution == "Ubuntu" and ansible_distribution_version == "24.04"
+
+- name: Remove old kernel
+  ansible.builtin.apt:
+    pkg:
+      - linux-image-virtual
+    autoremove: true
+    purge: true
+    state: absent
+  when:
+    - ansible_distribution == "Ubuntu" and ansible_distribution_version == "24.04"
diff --git a/ansible/tasks/setup-system.yml b/ansible/tasks/setup-system.yml
index 6777b7248..fda2627b1 100644
--- a/ansible/tasks/setup-system.yml
+++ b/ansible/tasks/setup-system.yml
@@ -91,6 +91,12 @@
   changed_when: false
   failed_when: false
 
+- name: Ensure guest VM time synchronisation
+  ansible.builtin.import_tasks:
+    file: tasks/setup-kvm-timesync.yml
+  when:
+    - qemu
+
 - name: Execute more tasks when stage1
   when: not stage2
   block: