[Skiboot] [PATCH 1/6] Enable attn instruction on boot

Michael Neuling mikey at neuling.org
Mon May 2 12:10:57 AEST 2016

On Fri, 2016-04-29 at 13:59 -0500, Patrick Williams wrote:
> On Fri, Apr 29, 2016 at 03:57:02PM +1000, Michael Neuling wrote:
> > 
> > Currently we leave the attn instruction disabled until we use.  This
> > means that attn is not available to the host kernel.
> > 
> > This enables the attn instruction on all CPUs on boot.
> > 
> > Signed-off-by: Michael Neuling <mikey at neuling.org>
> Are you sure this is a good idea?  I was under the impression that once
> the attn instruction is enabled any privilege level could execute it
> and it would actually cause an attn.  Are you certain that only
> hypervisor level code is able to execute attn and cause the effect?  You
> don't want to have virtual machines executing attn and bringing down
> your system.

Wow, I just checked on a real POWER8 and attn is enabled in problem state.

So yes, this is a colossally stupid idea!

> I can't find the instruction documented in the ISA (2.07 or 3.0) to know
> for certain.

... or in book 4.  It's not like it's important or anything!?!

Thanks for catch.


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