>On 24/07/2017 20:35, Peng Hao wrote:
>> When a windows vm starts, periodic timer of rtc will stop several times.
>> windows kernel will check whether REG_A_UIP is changed. REG_C's interrupt
>> flags will not be cleared when periodic timer stops and the update timer
>> will switch to alarm timer. So the expiration time of alarm timer is very
>> long and REG_A_UIP will not vary.At last windows kernel will repeat to
>> check REG_A_UIP all the time.
>This should not happen. REG_A_UIP is set and cleared in register A
>every second, like this:
> case RTC_REG_A:
> if (update_in_progress(s)) {
> s->cmos_data[s->cmos_index] |= REG_A_UIP
> } else {
> s->cmos_data[s->cmos_index] &= ~REG_A_UIP
> }
> ret = s->cmos_data[s->cmos_index]
> break
when periodic timer stop, update timer is set to a long expire time (as alarm
timer).
So update_in_progress always return 1 and REG_A_UIP is never cleared.
>where update_in_progress does:
> guest_nsec = get_guest_rtc_ns(s)
> /* UIP bit will be set at last 244us of every second. */
> if ((guest_nsec % NANOSECONDS_PER_SECOND) >=
> (NANOSECONDS_PER_SECOND - UIP_HOLD_LENGTH)) {
> return 1
> }
> return 0
>This is done even if the timer is not pending.
>How can the bug be reproduced?
many windows VMs reboot at the same time.some VM's vcpu thread go to a infinite
loop
at the starting stage.
>Paolo
> Signed-off-by: Peng Hao <peng.h...@zte.com.cn>
> Signed-off-by: Liu Yi <liu.y...@zte.com.cn>
> ---
> hw/timer/mc146818rtc.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/hw/timer/mc146818rtc.c b/hw/timer/mc146818rtc.c
> index 1b8d3d7..aa55fae 100644
> --- a/hw/timer/mc146818rtc.c
> +++ b/hw/timer/mc146818rtc.c
> @@ -457,6 +457,8 @@ static void rtc_update_timer(void *opaque)
> if ((new_irqs & s->cmos_data[RTC_REG_B]) != 0) {
> s->cmos_data[RTC_REG_C] |= REG_C_IRQF
> qemu_irq_raise(s->irq)
> + } else if ((s->cmos_data[RTC_REG_B] & REG_B_UIE) == 0) {
> + s->cmos_data[RTC_REG_C] &= ~REG_C_UF
> }
> check_update_timer(s)
> }
> @@ -559,7 +561,7 @@ static void cmos_ioport_write(void *opaque, hwaddr addr,
> s->cmos_data[RTC_REG_C] |= REG_C_IRQF
> qemu_irq_raise(s->irq)
> } else {
> - s->cmos_data[RTC_REG_C] &= ~REG_C_IRQF
> + s->cmos_data[RTC_REG_C] &= ~(REG_C_UF | REG_C_IRQF)
> qemu_irq_lower(s->irq)
> }
> s->cmos_data[RTC_REG_B] = data
>
