Re: [Qemu-devel] [PATCH] ps2: prevent changing irq state on save and load

["Pavel Dovgalyuk" <dovgaluk@ispras.ru>]

Paolo, have you forgot about this?

Pavel Dovgalyuk


> -----Original Message-----
> From: Paolo Bonzini [mailto:pbonzini@redhat.com]
> Sent: Friday, May 11, 2018 12:14 PM
> To: Pavel Dovgalyuk; qemu-devel@nongnu.org
> Cc: arei.gonglei@huawei.com; mst@redhat.com; ciro.santilli@gmail.com;
> maria.klimushenkova@ispras.ru; dovgaluk@ispras.ru; kraxel@redhat.com
> Subject: Re: [PATCH] ps2: prevent changing irq state on save and load
> 
> On 11/05/2018 10:16, Pavel Dovgalyuk wrote:
> > Commit 2858ab09e6f708e381fc1a1cc87e747a690c4884 changed
> > PS/2 keyboard/mouse buffers to the standard size. However, its state
> > may change when migrating from the old buffer size and therefore irq needs
> > updating. But this change made wrong, because it throws the whole queue
> > if there are too much data instead of cropping it.
> >
> > That commit also updates irq (because the queue state may change).
> > But updating the irq may change the VM state (and determinism of
> > the execution). E.g., when replaying the execution, one may save
> > the VM state and the state of the interrupt controller will be updated
> > at the moment of saving, instead of using the recorded update events.
> >
> > This patch makes the queue update deterministic: it removes the update_irq
> > call and crops the queue to prevent losing the characters and changing
> > the required irq status.
> >
> > Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>
> > ---
> >  hw/input/ps2.c |    8 ++++++--
> >  1 file changed, 6 insertions(+), 2 deletions(-)
> >
> > diff --git a/hw/input/ps2.c b/hw/input/ps2.c
> > index 06f5d2a..8b1931b 100644
> > --- a/hw/input/ps2.c
> > +++ b/hw/input/ps2.c
> > @@ -837,7 +837,12 @@ static void ps2_common_post_load(PS2State *s)
> >      uint8_t tmp_data[PS2_QUEUE_SIZE];
> >
> >      /* set the useful data buffer queue size, < PS2_QUEUE_SIZE */
> > -    size = (q->count < 0 || q->count > PS2_QUEUE_SIZE) ? 0 : q->count;
> > +    size = q->count;
> > +    if (q->count < 0) {
> > +        size = 0;
> > +    } else if (q->count > PS2_QUEUE_SIZE) {
> > +        size = PS2_QUEUE_SIZE;
> > +    }
> >
> >      /* move the queue elements to the start of data array */
> >      for (i = 0; i < size; i++) {
> > @@ -852,7 +857,6 @@ static void ps2_common_post_load(PS2State *s)
> >      q->rptr = 0;
> >      q->wptr = size;
> >      q->count = size;
> > -    s->update_irq(s->update_arg, q->count != 0);
> >  }
> >
> >  static void ps2_kbd_reset(void *opaque)
> >
> 
> Queued, thanks.
> 
> Paolo