Re: [PATCH 07/23] Add SLB switching code for entry/exit

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

On Wed, 2009-07-08 at 09:23 +0200, Alexander Graf wrote:
> Well, the problem is that we can't have two ESIDs for the same EA in  
> the SLB. So what I tried was to have guest ESIDs and host ESIDs  
> (PAGE_OFFSET+) live in the same SLB by removing the most significant  
> bit of the guest ESID.

I'll reply to that later when I understand what you are doing better.

> Yikes. So pHyp restores SLB entries from a shadow? Sounds like I need  
> to mess with that one too :-(.

Right.

> I'm not really fond of all the SLB switching code in general. Best  
> case would probably be to have a host and guest shadow SLB in the RMA  
> that the real mode code can take to switch the _full_ SLB.
> 
> That way we'd also get rid of the CONTEXT_GUEST stuff in the kernel  
> module, where we are in Linux, but have guest SLB entries active  
> already.

Same comment as above :-) I'm sure together we can come up with
something quite optimal but I need to catch up a bit first :-)

> Any reason it doesn't work on Power3? :-). It definitely does not work  
> on iSeries, though the code could be made to work there FWIW.

On Power3 you'd have to implement STAB support instead of SLB (get
yourself a PowerPC Book3 pre-2.0 if that's available publically and you
are masochist :-)

On legacy iSeries, it's harder, you don't have access to real mode and
the hypervisor is more invasive. I wouldn't bother with these. Any
recent iSeries (POWER5 or later) uses pHyp and so shouldn't be a
problem.

Cheers
Ben.