Re: [PATCH 1/2] powerpc: add Book E support to 64-bit hibernation

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Mon, 2013-06-17 at 19:22 -0500, Scott Wood wrote:
> On 06/17/2013 07:17:30 PM, Benjamin Herrenschmidt wrote:
> > On Mon, 2013-06-17 at 19:01 -0500, Scott Wood wrote:
> > > I really doubt the exception scratch registers need to be saved --
> > > we're not trying to restore into the middle of an exception
> > > prolog/epilog.
> > >
> > > book3s has the PACA as well and they don't save it.  Don't we rely  
> > on
> > > things like boot-time memory allocations happening in the same place
> > > when we resume?  extlb is part of the PACA, so the same applies.
> > 
> > I doubt we seriously tested hibernation :-) The PACA SPR should
> > definitely be saved/restored.
> 
> OK.  It's not obvious to me how much the entire mechanism depends on  
> things like boot time allocations being the same each time -- if we do  
> depend on that in general, then the PACA shouldn't change on a  
> particular CPU, right?

No we shouldn't be depending on that stuff.

> Is it possible to restore on a different CPU than we saved on?  If so,  
> could restoring the PACA leave us pointing to a different CPU's PACA?

Today on your code no, but of course this needs to be handled, the PACA
should be restored along with other thing, but for the right
processor :-)

Cheers,
Ben.