Re: [Xen-devel] [PATCH 1/6] x86/HVM: fix processing of RTC REG_B writes

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 02.05.13 at 11:21, Tim Deegan <tim@xxxxxxx> wrote:
> At 14:51 +0100 on 29 Apr (1367247101), Jan Beulich wrote:
>> We must store the new values before calling rtc_update_irq(), and we
>> need to call rtc_timer_update() when PIE transitions from 0 to 1 (as we
>> may have previously turned off the periodic timer due to the guest not
>> reading REG_C, and hence may have to re-enable it in order to start
>> IRQs getting delivered to the guest).
>> 
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>> 
>> --- a/xen/arch/x86/hvm/rtc.c
>> +++ b/xen/arch/x86/hvm/rtc.c
>> @@ -468,12 +468,14 @@ static int rtc_ioport_write(void *opaque
>>              if ( orig & RTC_SET )
>>                  rtc_set_time(s);
>>          }
>> +        s->hw.cmos_data[RTC_REG_B] = data;
>>          /*
>>           * If the interrupt is already set when the interrupt becomes
>>           * enabled, raise an interrupt immediately.
>>           */
>>          rtc_update_irq(s);
>> -        s->hw.cmos_data[RTC_REG_B] = data;
>> +        if ( (data & RTC_PIE) && !(orig & RTC_PIE) )
>> +            rtc_timer_update(s);
> 
> Shouldn't this be 'if ( (data ^ orig) & RTC_PIE )'? You'll want to
> disable the timer if the interrupt's been turned off.

No, in the spirit of the other involved code we'll want to keep it
running until reaching dead_ticks.

Jan


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