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

[Tim Deegan <tim@xxxxxxx>]

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.

Tim.

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