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migration: Do not re-read the clock on pre_save in case of paused guest 

Re-read the timebase before migrate was ported from x86 commit:
   6053a86fe7bd: kvmclock: reduce kvmclock difference on migration

The clock move makes the guest knows about the paused time between
the stop and migrate commands. This is an issue in an already-paused
VM because some side effects, like process stalls, could happen
after migration.

So, this patch checks the runstate of guest in the pre_save handler and
do not re-reads the timebase in case of paused state (cold migration).

Signed-off-by: Maxiwell S. Garcia <maxiwell@linux.ibm.com>
Message-Id: <20190711194702.26598-1-maxiwell@linux.ibm.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
master
Maxiwell S. Garcia 2019-07-11 16:47:02 -03:00 committed by David Gibson
parent d15d4ad64f
commit d14f339762
2 changed files with 10 additions and 4 deletions
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13
hw/ppc/ppc.c
View File

@ -1011,6 +1011,8 @@ static void timebase_save(PPCTimebase *tb)
* there is no need to update it from KVM here
*/
tb->guest_timebase = ticks + first_ppc_cpu->env.tb_env->tb_offset;
tb->runstate_paused = runstate_check(RUN_STATE_PAUSED);
}
static void timebase_load(PPCTimebase *tb)
@ -1054,9 +1056,9 @@ void cpu_ppc_clock_vm_state_change(void *opaque, int running,
}
/*
* When migrating, read the clock just before migration,
* so that the guest clock counts during the events
* between:
* When migrating a running guest, read the clock just
* before migration, so that the guest clock counts
* during the events between:
*
* * vm_stop()
* *
@ -1071,7 +1073,10 @@ static int timebase_pre_save(void *opaque)
{
PPCTimebase *tb = opaque;
timebase_save(tb);
/* guest_timebase won't be overridden in case of paused guest */
if (!tb->runstate_paused) {
timebase_save(tb);
}
return 0;
}

1
target/ppc/cpu-qom.h
View File

@ -201,6 +201,7 @@ typedef struct PowerPCCPUClass {
typedef struct PPCTimebase {
uint64_t guest_timebase;
int64_t time_of_the_day_ns;
bool runstate_paused;
} PPCTimebase;
extern const VMStateDescription vmstate_ppc_timebase;