On Thu, Jul 11, 2019 at 04:47:02PM -0300, Maxiwell S. Garcia wrote: > 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 <maxiw...@linux.ibm.com>
I've applied this to ppc-for-4.2. I think it probably is a correct
fix, but this could have subtle impacts on things that are mostly
working at the moment, so I don't want to risk it during hard freeze.
> ---
> hw/ppc/ppc.c | 13 +++++++++----
> target/ppc/cpu-qom.h | 1 +
> 2 files changed, 10 insertions(+), 4 deletions(-)
>
> diff --git a/hw/ppc/ppc.c b/hw/ppc/ppc.c
> index a9e508c496..8572e45274 100644
> --- a/hw/ppc/ppc.c
> +++ b/hw/ppc/ppc.c
> @@ -1008,6 +1008,8 @@ 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)
> @@ -1051,9 +1053,9 @@ 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()
> * *
> @@ -1068,7 +1070,10 @@ 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;
> }
> diff --git a/target/ppc/cpu-qom.h b/target/ppc/cpu-qom.h
> index be9b4c30c3..5fbcdee9c9 100644
> --- a/target/ppc/cpu-qom.h
> +++ b/target/ppc/cpu-qom.h
> @@ -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 struct VMStateDescription vmstate_ppc_timebase;
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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