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ptp: vmclock: add vm generation counter

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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>
This commit is contained in:
Babis Chalios 2026-01-30 17:36:00 +00:00 committed by Jakub Kicinski
parent 8755aae4aa
commit 3495064b6d
1 changed files with 15 additions and 0 deletions
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15
include/uapi/linux/vmclock-abi.h
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@ -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__ */