* Pavel Dovgalyuk ([email protected]) wrote: > > From: Dr. David Alan Gilbert [mailto:[email protected]] > > * Pavel Dovgalyuk ([email protected]) wrote: > > > HPET saves its state by calculating the current time and recovers timer > > > offset using this calculated value. But these calculations include > > > divisions and multiplications. Therefore the timer state cannot be > > > recovered > > > precise enough. > > > This patch introduces saving of the original value of the offset to > > > preserve the determinism of the timer. > > > > Please put the extra data in a subsection and tie the subsection to a > > property enabled by the machine type. That avoids breaking backwards > > migration compatibility. > > I thought about it and haven't found how to preserve the backward migration > compatibility > without breaking everything else. > Loading old (or compatible) snapshot without changing the version will > corrupt the offset in > post_load.
There are lots of ways; for example you could initialise hpet_offset to a dummy value in a pre-load and spot that in the post-load instead of the version_id, or set a flag in a post-load on the subsection. Dave > Pavel Dovgalyuk > > > > > Signed-off-by: Maria Klimushenkova <[email protected]> > > > Signed-off-by: Pavel Dovgalyuk <[email protected]> > > > > > > --- > > > hw/timer/hpet.c | 12 +++++++++--- > > > 1 file changed, 9 insertions(+), 3 deletions(-) > > > > > > diff --git a/hw/timer/hpet.c b/hw/timer/hpet.c > > > index 577371b..4cf6a5b 100644 > > > --- a/hw/timer/hpet.c > > > +++ b/hw/timer/hpet.c > > > @@ -221,7 +221,9 @@ static int hpet_pre_save(void *opaque) > > > HPETState *s = opaque; > > > > > > /* save current counter value */ > > > - s->hpet_counter = hpet_get_ticks(s); > > > + if (hpet_enabled(s)) { > > > + s->hpet_counter = hpet_get_ticks(s); > > > + } > > > > > > return 0; > > > } > > > @@ -252,7 +254,10 @@ static int hpet_post_load(void *opaque, int > > > version_id) > > > HPETState *s = opaque; > > > > > > /* Recalculate the offset between the main counter and guest time */ > > > - s->hpet_offset = ticks_to_ns(s->hpet_counter) - > > > qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL); > > > + if (version_id <= 2) { > > > + s->hpet_offset = ticks_to_ns(s->hpet_counter) > > > + - qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL); > > > + } > > > > > > /* Push number of timers into capability returned via HPET_ID */ > > > s->capability &= ~HPET_ID_NUM_TIM_MASK; > > > @@ -303,7 +308,7 @@ static const VMStateDescription vmstate_hpet_timer = { > > > > > > static const VMStateDescription vmstate_hpet = { > > > .name = "hpet", > > > - .version_id = 2, > > > + .version_id = 3, > > > .minimum_version_id = 1, > > > .pre_save = hpet_pre_save, > > > .pre_load = hpet_pre_load, > > > @@ -312,6 +317,7 @@ static const VMStateDescription vmstate_hpet = { > > > VMSTATE_UINT64(config, HPETState), > > > VMSTATE_UINT64(isr, HPETState), > > > VMSTATE_UINT64(hpet_counter, HPETState), > > > + VMSTATE_UINT64_V(hpet_offset, HPETState, 3), > > > VMSTATE_UINT8_V(num_timers, HPETState, 2), > > > VMSTATE_VALIDATE("num_timers in range", > > > hpet_validate_num_timers), > > > VMSTATE_STRUCT_VARRAY_UINT8(timer, HPETState, num_timers, 0, > > > > > -- > > Dr. David Alan Gilbert / [email protected] / Manchester, UK > -- Dr. David Alan Gilbert / [email protected] / Manchester, UK
