Re: [Qemu-devel] [PATCH v2] hpet: recover timer offset correctly

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

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Pavel Dovgalyuk

> -----Original Message-----
> From: Pavel Dovgalyuk [mailto:Pavel.Dovgaluk@ispras.ru]
> Sent: Wednesday, December 20, 2017 1:02 PM
> To: qemu-devel@nongnu.org
> Cc: quintela@redhat.com; mst@redhat.com; dgilbert@redhat.com; maria.klimushenkova@ispras.ru;
> dovgaluk@ispras.ru; pavel.dovgaluk@ispras.ru; pbonzini@redhat.com
> Subject: [PATCH v2] hpet: recover timer offset correctly
> 
> 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.
> 
> Signed-off-by: Maria Klimushenkova <maria.klimushenkova@ispras.ru>
> Signed-off-by: Pavel Dovgalyuk <pavel.dovgaluk@ispras.ru>
> ---
>  hw/timer/hpet.c |   32 ++++++++++++++++++++++++++++++--
>  1 file changed, 30 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/timer/hpet.c b/hw/timer/hpet.c
> index 577371b..4904a60 100644
> --- a/hw/timer/hpet.c
> +++ b/hw/timer/hpet.c
> @@ -70,6 +70,7 @@ typedef struct HPETState {
> 
>      MemoryRegion iomem;
>      uint64_t hpet_offset;
> +    bool hpet_offset_loaded;
>      qemu_irq irqs[HPET_NUM_IRQ_ROUTES];
>      uint32_t flags;
>      uint8_t rtc_irq_level;
> @@ -221,7 +222,9 @@ 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;
>  }
> @@ -232,6 +235,8 @@ static int hpet_pre_load(void *opaque)
> 
>      /* version 1 only supports 3, later versions will load the actual value */
>      s->num_timers = HPET_MIN_TIMERS;
> +    /* for checking whether the hpet_offset section is loaded */
> +    s->hpet_offset_loaded = false;
>      return 0;
>  }
> 
> @@ -252,7 +257,10 @@ 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 (!s->hpet_offset_loaded) {
> +        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;
> @@ -267,6 +275,14 @@ static int hpet_post_load(void *opaque, int version_id)
>      return 0;
>  }
> 
> +static int hpet_offset_post_load(void *opaque, int version_id)
> +{
> +    HPETState *s = opaque;
> +
> +    s->hpet_offset_loaded = true;
> +    return 0;
> +}
> +
>  static bool hpet_rtc_irq_level_needed(void *opaque)
>  {
>      HPETState *s = opaque;
> @@ -285,6 +301,17 @@ static const VMStateDescription vmstate_hpet_rtc_irq_level = {
>      }
>  };
> 
> +static const VMStateDescription vmstate_hpet_offset = {
> +    .name = "hpet/offset",
> +    .version_id = 1,
> +    .minimum_version_id = 1,
> +    .post_load = hpet_offset_post_load,
> +    .fields = (VMStateField[]) {
> +        VMSTATE_UINT64(hpet_offset, HPETState),
> +        VMSTATE_END_OF_LIST()
> +    }
> +};
> +
>  static const VMStateDescription vmstate_hpet_timer = {
>      .name = "hpet_timer",
>      .version_id = 1,
> @@ -320,6 +347,7 @@ static const VMStateDescription vmstate_hpet = {
>      },
>      .subsections = (const VMStateDescription*[]) {
>          &vmstate_hpet_rtc_irq_level,
> +        &vmstate_hpet_offset,
>          NULL
>      }
>  };