On 25/07/2017 11:29, peng.h...@zte.com.cn wrote:
>>On 25/07/2017 06:14, peng.h...@zte.com.cn wrote:
>
>>>> 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).
>
>>I think I see the bug now:
>
>>diff --git a/hw/timer/mc146818rtc.c b/hw/timer/mc146818rtc.c
>>index 1b8d3d7d4c..6184b4378e 100644
>>--- a/hw/timer/mc146818rtc.c
>>+++ b/hw/timer/mc146818rtc.c
>>@@ -321,9 +321,11 @@ static void check_update_timer(RTCState *s)
>> s->next_alarm_time = next_update_time +
>> (next_alarm_sec - 1) * NANOSECONDS_PER_SECOND;
>>
>>- if (s->cmos_data[RTC_REG_C] & REG_C_UF) {
>>- /* UF is set, but AF is clear. Program the timer to target
>>- * the alarm time. */
>>+ if ((s->cmos_data[RTC_REG_C] & REG_C_UF) &&
>>+ !(s->cmos_data[RTC_REG_A] & REG_A_UIP)) {
>>+ /* If UIP was latched, we need to clear it at the next update.
>>+ * Otherwise, if UF is set we only need to program the timer to
>>+ * target the alarm time. */
>> next_update_time = s->next_alarm_time;
>> }
>> if (next_update_time != timer_expire_time_ns(s->update_timer)) {
>>
>>but I would like to have a testcase for it in tests/rtc-test.c.
>>Can you check if the above works and try writing a testcase (that fails
>>without the patch and succeeds with it)?
>>Thanks,
>
> I don't think it can works.
Have you tested it?
> REG_C_UF is totally cleared by periodic timer in original code.
> after periodic timer stoped, the REG_C_UF is never cleared.
Your patch cleared REG_C_UF, but you have not said why the actual
hardware would clear REG_C_UF (it wouldn't).
> rtc_update_timer has cleared REG_A_UIP,I think the patch does nothing.
>
> I reproduce the bug when many windows VMs reboot and it is about the
> method of windows kernel accessing rtc .
>
> so i don't know how to write the testcase.
First of all you have to describe the exact sequence of register
accesses that causes the problem. I can help you writing the testcase,
but your changes to the device model must reflect the actual behavior of
the hardware.
Paolo
