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Re: [Qemu-devel] [PATCH V3] rtc: fix a infinite loop in windows vm start
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH V3] rtc: fix a infinite loop in windows vm startup |
Date: |
Mon, 24 Jul 2017 13:53:04 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 |
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;
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?
Paolo
> Signed-off-by: Peng Hao <address@hidden>
> Signed-off-by: Liu Yi <address@hidden>
> ---
> 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;
>