Re: [PATCH] hw/i8254: fix vmstate load

[Dr. David Alan Gilbert]

* Pavel Dovgalyuk (pavel.dovgalyuk@ispras.ru) wrote:
> On 15.03.2021 23:13, Dr. David Alan Gilbert wrote:
> > * Pavel Dovgalyuk (pavel.dovgalyuk@ispras.ru) wrote:
> > > QEMU timer of channel 0 in i8254 is used to raise irq
> > > at the specified moment of time. This irq can be disabled
> > > with irq_disabled flag. But when vmstate of the pit is
> > > loaded, timer may be rearmed despite the disabled interrupts.
> > > This patch adds irq_disabled flag check to fix that.
> > > 
> > > Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgalyuk@ispras.ru>
> > 
> > Hi Pavel,
> >    I'm curious, did you see this cause a problem on a particular guest
> > OS?
> 
> That was Windows 7 on i386.
> I found this when tested reverse debugging.

Thanks; I like to know of migration fixes for when someone comes asking
why something obscure breaks under migration :-)

Dave

> > 
> > Dave
> > 
> > > ---
> > >   hw/timer/i8254.c |    2 +-
> > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/hw/timer/i8254.c b/hw/timer/i8254.c
> > > index c01ee2c72a..c8388ea432 100644
> > > --- a/hw/timer/i8254.c
> > > +++ b/hw/timer/i8254.c
> > > @@ -324,7 +324,7 @@ static void pit_post_load(PITCommonState *s)
> > >   {
> > >       PITChannelState *sc = &s->channels[0];
> > > -    if (sc->next_transition_time != -1) {
> > > +    if (sc->next_transition_time != -1 && !sc->irq_disabled) {
> > >           timer_mod(sc->irq_timer, sc->next_transition_time);
> > >       } else {
> > >           timer_del(sc->irq_timer);
> > > 
> > > 
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK