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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>

authored by

Babis Chalios and committed by
Jakub Kicinski 3495064b 8755aae4

+15
+15
include/uapi/linux/vmclock-abi.h
··· 115 115 * bit again after the update, using the about-to-be-valid fields. 116 116 */ 117 117 #define VMCLOCK_FLAG_TIME_MONOTONIC (1 << 7) 118 + /* 119 + * If the VM_GEN_COUNTER_PRESENT flag is set, the hypervisor will 120 + * bump the vm_generation_counter field every time the guest is 121 + * loaded from some save state (restored from a snapshot). 122 + */ 123 + #define VMCLOCK_FLAG_VM_GEN_COUNTER_PRESENT (1 << 8) 118 124 119 125 __u8 pad[2]; 120 126 __u8 clock_status; ··· 183 177 __le64 time_frac_sec; /* Units of 1/2^64 of a second */ 184 178 __le64 time_esterror_nanosec; 185 179 __le64 time_maxerror_nanosec; 180 + 181 + /* 182 + * This field changes to another non-repeating value when the guest 183 + * has been loaded from a snapshot. In addition to handling a 184 + * disruption in time (which will also be signalled through the 185 + * disruption_marker field), a guest may wish to discard UUIDs, 186 + * reset network connections, reseed entropy, etc. 187 + */ 188 + __le64 vm_generation_counter; 186 189 }; 187 190 188 191 #endif /* __VMCLOCK_ABI_H__ */