[1/2] hw/audio/hda-codec: fix multiplication overflow

After a relatively short time, there is an multiplication overflow
when multiplying (now - buft_start) with hda_bytes_per_second().
While the uptime now - buft_start only overflows after 2**63 ns
= 292.27 years, this happens hda_bytes_per_second() times faster
with the multiplication. At 44100 samples/s * 2 channels
* 2 bytes/channel = 176400 bytes/s that is 14.52 hours. After the
multiplication overflow the affected audio stream stalls.

Replace the multiplication and following division with muldiv64()
to prevent a multiplication overflow.

Fixes: 280c1e1cdb ("audio/hda: create millisecond timers that handle IO")
Reported-by: M_O_Bz <m_o_bz@163.com>
Signed-off-by: Volker Rümelin <vr_qemu@t-online.de>
---
 hw/audio/hda-codec.c | 29 +++++++++++++++++++++--------
 1 file changed, 21 insertions(+), 8 deletions(-)

On Sun, Nov 5, 2023 at 9:26 PM Volker Rümelin <vr_qemu@t-online.de> wrote:
>
> After a relatively short time, there is an multiplication overflow
> when multiplying (now - buft_start) with hda_bytes_per_second().
> While the uptime now - buft_start only overflows after 2**63 ns
> = 292.27 years, this happens hda_bytes_per_second() times faster
> with the multiplication. At 44100 samples/s * 2 channels
> * 2 bytes/channel = 176400 bytes/s that is 14.52 hours. After the
> multiplication overflow the affected audio stream stalls.
>
> Replace the multiplication and following division with muldiv64()
> to prevent a multiplication overflow.
>
> Fixes: 280c1e1cdb ("audio/hda: create millisecond timers that handle IO")
> Reported-by: M_O_Bz <m_o_bz@163.com>
> Signed-off-by: Volker Rümelin <vr_qemu@t-online.de>

Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>

> ---
>  hw/audio/hda-codec.c | 29 +++++++++++++++++++++--------
>  1 file changed, 21 insertions(+), 8 deletions(-)
>
> diff --git a/hw/audio/hda-codec.c b/hw/audio/hda-codec.c
> index b9ad1f4c39..f756e419bb 100644
> --- a/hw/audio/hda-codec.c
> +++ b/hw/audio/hda-codec.c
> @@ -22,6 +22,7 @@
>  #include "hw/qdev-properties.h"
>  #include "intel-hda.h"
>  #include "migration/vmstate.h"
> +#include "qemu/host-utils.h"
>  #include "qemu/module.h"
>  #include "intel-hda-defs.h"
>  #include "audio/audio.h"
> @@ -189,9 +190,9 @@ struct HDAAudioState {
>      bool     use_timer;
>  };
>
> -static inline int64_t hda_bytes_per_second(HDAAudioStream *st)
> +static inline uint32_t hda_bytes_per_second(HDAAudioStream *st)
>  {
> -    return 2LL * st->as.nchannels * st->as.freq;
> +    return 2 * (uint32_t)st->as.nchannels * (uint32_t)st->as.freq;
>  }
>
>  static inline void hda_timer_sync_adjust(HDAAudioStream *st, int64_t target_pos)
> @@ -222,12 +223,18 @@ static void hda_audio_input_timer(void *opaque)
>
>      int64_t now = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
>
> -    int64_t buft_start = st->buft_start;
> +    int64_t uptime = now - st->buft_start;
>      int64_t wpos = st->wpos;
>      int64_t rpos = st->rpos;
> +    int64_t wanted_rpos;
>
> -    int64_t wanted_rpos = hda_bytes_per_second(st) * (now - buft_start)
> -                          / NANOSECONDS_PER_SECOND;
> +    if (uptime <= 0) {
> +        /* wanted_rpos <= 0 */
> +        goto out_timer;
> +    }
> +
> +    wanted_rpos = muldiv64(uptime, hda_bytes_per_second(st),
> +                           NANOSECONDS_PER_SECOND);
>      wanted_rpos &= -4; /* IMPORTANT! clip to frames */
>
>      if (wanted_rpos <= rpos) {
> @@ -286,12 +293,18 @@ static void hda_audio_output_timer(void *opaque)
>
>      int64_t now = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
>
> -    int64_t buft_start = st->buft_start;
> +    int64_t uptime = now - st->buft_start;
>      int64_t wpos = st->wpos;
>      int64_t rpos = st->rpos;
> +    int64_t wanted_wpos;
> +
> +    if (uptime <= 0) {
> +        /* wanted_wpos <= 0 */
> +        goto out_timer;
> +    }
>
> -    int64_t wanted_wpos = hda_bytes_per_second(st) * (now - buft_start)
> -                          / NANOSECONDS_PER_SECOND;
> +    wanted_wpos = muldiv64(uptime, hda_bytes_per_second(st),
> +                           NANOSECONDS_PER_SECOND);
>      wanted_wpos &= -4; /* IMPORTANT! clip to frames */
>
>      if (wanted_wpos <= wpos) {
> --
> 2.35.3
>
>