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kvmclock: fix clock_is_reliable on migration from QEMU < 2.9 

When migrating from a pre-2.9 QEMU, no clock_is_reliable flag is
transferred. We should assume that the source host has an unreliable
KVM_GET_CLOCK, rather than using whatever was determined locally, to
ensure that any drift from the TSC-based value calculated by the guest
is corrected.

Signed-off-by: Michael Chapman <mike@very.puzzling.org>
Message-Id: <20180406053406.774-1-mike@very.puzzling.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Michael Chapman 2018-04-06 15:34:06 +10:00 committed by Paolo Bonzini
parent 4968a2c6ed
commit c2b01cfec1
1 changed files with 14 additions and 0 deletions
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14
hw/i386/kvm/clock.c
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@ -241,6 +241,19 @@ static const VMStateDescription kvmclock_reliable_get_clock = {
}
};
/*
* When migrating, assume the source has an unreliable
* KVM_GET_CLOCK unless told otherwise.
*/
static int kvmclock_pre_load(void *opaque)
{
KVMClockState *s = opaque;
s->clock_is_reliable = false;
return 0;
}
/*
* When migrating, read the clock just before migration,
* so that the guest clock counts during the events
@ -268,6 +281,7 @@ static const VMStateDescription kvmclock_vmsd = {
.name = "kvmclock",
.version_id = 1,
.minimum_version_id = 1,
.pre_load = kvmclock_pre_load,
.pre_save = kvmclock_pre_save,
.fields = (VMStateField[]) {
VMSTATE_UINT64(clock, KVMClockState),