ptp: vmclock: add vm generation counter

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>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
Tested-by: Takahiro Itazur <itazur@amazon.com>
Link: https://patch.msgid.link/20260130173704.12575-2-itazur@amazon.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/include/uapi/linux/vmclock-abi.h b/include/uapi/linux/vmclock-abi.h
index 2d99b29ac44aec5309350c63f6f55e77f2a7bd68..937fe00e4f336b73f92fbd7ae3396c21e937e203 100644 (file)
--- 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__ */