[PATCH 10/13] kvm/powerpc: Add support for Book3S processors in hypervisor mode

[Alexander Graf]

On 27.05.2011, at 12:33, Paul Mackerras wrote:

> On Tue, May 17, 2011 at 12:17:50PM +0200, Alexander Graf wrote:
>> 
>> On 16.05.2011, at 07:58, Paul Mackerras wrote:
>> 
>>> 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.

Please try to contact some of your hardware designers and figure out what exactly the conditions are. Maybe we don't need this hack.

Alex