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Tue, 25 Nov 2025 15:38:31 +0000 Received: from EX19D012EUA001.ant.amazon.com ([fe80::b7ea:84f7:2c4b:2719]) by EX19D012EUA001.ant.amazon.com ([fe80::b7ea:84f7:2c4b:2719%3]) with mapi id 15.02.2562.029; Tue, 25 Nov 2025 15:38:31 +0000 From: "Chalios, Babis" To: "richardcochran@gmail.com" , "dwmw2@infradead.org" , "andrew+netdev@lunn.ch" , "davem@davemloft.net" , "edumazet@google.com" , "kuba@kernel.org" , "pabeni@redhat.com" , "netdev@vger.kernel.org" , "linux-kernel@vger.kernel.org" CC: "Chalios, Babis" , "Graf (AWS), Alexander" , "mzxreary@0pointer.de" Subject: [RFC PATCH 0/2] ptp: vmclock: Add VM generation counter and ACPI notification Thread-Topic: [RFC PATCH 0/2] ptp: vmclock: Add VM generation counter and ACPI notification Thread-Index: AQHcXiGN5TmpWOFD50aX4v9BFCAgDw== Date: Tue, 25 Nov 2025 15:38:31 +0000 Message-ID: <20251125153830.11487-1-bchalios@amazon.es> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Similarly to live migration, starting a VM from some serialized state=0A= (aka snapshot) is an event which calls for adjusting guest clocks, hence=0A= a hypervisor should increase the disruption_marker before resuming the=0A= VM vCPUs, letting the guest know.=0A= =0A= However, loading a snapshot, is slightly different than live migration,=0A= especially since we can start multiple VMs from the same serialized=0A= state. Apart from adjusting clocks, the guest needs to take additional=0A= action during such events, e.g. recreate UUIDs, reset network=0A= adapters/connections, reseed entropy pools, etc. These actions are not=0A= necessary during live migration. This calls for a differentiation=0A= between the two triggering events.=0A= =0A= We differentiate between the two events via an extra field in the=0A= vmclock_abi, called vm_generation_counter. Whereas hypervisors should=0A= increase the disruption marker in both cases, they should only increase=0A= vm_generation_counter when a snapshot is loaded in a VM (not during live=0A= migration).=0A= =0A= Additionally, we attach an ACPI notification to VMClock. Hypervisors=0A= should execute an ACPI notify operation every time seq_count changes to=0A= an even number. We implement the poll() interface for VMClock device.=0A= listeners of poll() will be notified about changes in the ABI every time=0A= the hypervisor sends us a notification.=0A= =0A= Babis Chalios (2):=0A= ptp: vmclock: add vm generation counter=0A= ptp: vmclock: support device notifications=0A= =0A= drivers/ptp/ptp_vmclock.c | 85 ++++++++++++++++++++++++++++++--=0A= include/uapi/linux/vmclock-abi.h | 19 +++++++=0A= 2 files changed, 99 insertions(+), 5 deletions(-)=0A= =0A= -- =0A= 2.34.1=0A= =0A=