From: "Chalios, Babis" <bchalios@amazon•es>
To: "robh@kernel•org" <robh@kernel•org>,
"krzk+dt@kernel•org" <krzk+dt@kernel•org>,
"conor+dt@kernel•org" <conor+dt@kernel•org>,
"richardcochran@gmail•com" <richardcochran@gmail•com>,
"dwmw2@infradead•org" <dwmw2@infradead•org>,
"andrew+netdev@lunn•ch" <andrew+netdev@lunn•ch>,
"davem@davemloft•net" <davem@davemloft•net>,
"edumazet@google•com" <edumazet@google•com>,
"kuba@kernel•org" <kuba@kernel•org>,
"pabeni@redhat•com" <pabeni@redhat•com>
Cc: "devicetree@vger•kernel.org" <devicetree@vger•kernel.org>,
"netdev@vger•kernel.org" <netdev@vger•kernel.org>,
"linux-kernel@vger•kernel.org" <linux-kernel@vger•kernel.org>,
"Chalios, Babis" <bchalios@amazon•es>, "Graf (AWS),
Alexander" <graf@amazon•de>,
"mzxreary@0pointer•de" <mzxreary@0pointer•de>,
"Cali, Marco" <xmarcalx@amazon•co.uk>,
"Woodhouse, David" <dwmw@amazon•co.uk>
Subject: [PATCH v5 1/7] ptp: vmclock: add vm generation counter
Date: Wed, 7 Jan 2026 13:25:27 +0000 [thread overview]
Message-ID: <20260107132514.437-2-bchalios@amazon.es> (raw)
In-Reply-To: <20260107132514.437-1-bchalios@amazon.es>
Similar to live migration, loading a VM from some saved state (aka
snapshot) is also an event that calls for clock adjustments in the
guest. However, guests might want to take more actions as a response to
such events, e.g. as discarding UUIDs, resetting network connections,
reseeding entropy pools, etc. These are actions that guests don't
typically take during live migration, so add a new field in the
vmclock_abi called vm_generation_counter which informs the guest about
such events.
Hypervisor advertises support for vm_generation_counter through the
VMCLOCK_FLAG_VM_GEN_COUNTER_PRESENT flag. Users need to check the
presence of this bit in vmclock_abi flags field before using this flag.
Signed-off-by: Babis Chalios <bchalios@amazon•es>
Reviewed-by: David Woodhouse <dwmw@amazon•co.uk>
---
include/uapi/linux/vmclock-abi.h | 15 +++++++++++++++
1 file changed, 15 insertions(+)
diff --git a/include/uapi/linux/vmclock-abi.h b/include/uapi/linux/vmclock-abi.h
index 2d99b29ac44a..937fe00e4f33 100644
--- a/include/uapi/linux/vmclock-abi.h
+++ b/include/uapi/linux/vmclock-abi.h
@@ -115,6 +115,12 @@ struct vmclock_abi {
* bit again after the update, using the about-to-be-valid fields.
*/
#define VMCLOCK_FLAG_TIME_MONOTONIC (1 << 7)
+ /*
+ * If the VM_GEN_COUNTER_PRESENT flag is set, the hypervisor will
+ * bump the vm_generation_counter field every time the guest is
+ * loaded from some save state (restored from a snapshot).
+ */
+#define VMCLOCK_FLAG_VM_GEN_COUNTER_PRESENT (1 << 8)
__u8 pad[2];
__u8 clock_status;
@@ -177,6 +183,15 @@ struct vmclock_abi {
__le64 time_frac_sec; /* Units of 1/2^64 of a second */
__le64 time_esterror_nanosec;
__le64 time_maxerror_nanosec;
+
+ /*
+ * This field changes to another non-repeating value when the guest
+ * has been loaded from a snapshot. In addition to handling a
+ * disruption in time (which will also be signalled through the
+ * disruption_marker field), a guest may wish to discard UUIDs,
+ * reset network connections, reseed entropy, etc.
+ */
+ __le64 vm_generation_counter;
};
#endif /* __VMCLOCK_ABI_H__ */
--
2.34.1
next prev parent reply other threads:[~2026-01-07 13:26 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-01-07 13:25 [PATCH v5 0/7] ptp: vmclock: Add VM generation counter and ACPI notification Chalios, Babis
2026-01-07 13:25 ` Chalios, Babis [this message]
2026-01-07 13:25 ` [PATCH v5 2/7] ptp: vmclock: support device notifications Chalios, Babis
2026-01-07 13:25 ` [PATCH v5 3/7] dt-bindings: ptp: Add amazon,vmclock Chalios, Babis
2026-01-07 13:26 ` [PATCH v5 4/7] ptp: ptp_vmclock: Add device tree support Chalios, Babis
2026-01-13 3:46 ` Jakub Kicinski
2026-01-07 13:26 ` [PATCH v5 5/7] ptp: ptp_vmclock: add 'VMCLOCK' to ACPI device match Chalios, Babis
2026-01-07 13:26 ` [PATCH v5 6/7] ptp: ptp_vmclock: remove dependency on CONFIG_ACPI Chalios, Babis
2026-01-07 13:26 ` [PATCH v5 7/7] ptp: ptp_vmclock: return TAI not UTC Chalios, Babis
2026-01-07 13:28 ` [PATCH v5 0/7] ptp: vmclock: Add VM generation counter and ACPI notification David Woodhouse
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