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

[Paolo Bonzini]

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 <address@hidden>
> ---
>  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