[PATCH 10/13] kvm/powerpc: Add support for Book3S processors in hypervisor mode
Segher Boessenkool
segher at kernel.crashing.org
Sat May 28 06:59:41 EST 2011
>>> I do the check there because I was having problems where, if the HDEC
>>> goes negative before we do the partition switch, we would
>>> occasionally
>>> not get the HDEC interrupt at all until the next time HDEC went
>>> negative, ~ 8.4 seconds later.
>>
>> Yikes - so HDEC is edge and doesn't even keep the interrupt line up?
>> That sounds like a serious hardware limitation. What if you only use
>> HDEC and it triggers while interrupts are off in a critical section?
>> Is the hardware really that broken?
>
> If HDEC expires when interrupts are off, the HDEC interrupt stays
> pending until interrupts get re-enabled. I'm not sure exactly what
> the conditions are that cause an HDEC interrupt to get lost, but they
> seem to involve at least a partition switch.
On some CPUs, if the top bit of the decrementer is 0 again when you
re-enable
the interrupt, the interrupt is lost (so it is actually
level-triggered).
The arch books talk a bit about this AFAIR.
Segher
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