Re: [Qemu-devel] [PATCH] Fix a bug in mtsr/mtsrin emulation on ppc64

[David Gibson <david@gibson.dropbear.id.au>]

On Sat, May 21, 2011 at 11:46:12AM +0200, Alexander Graf wrote:
> 
> On 21.05.2011, at 11:40, Andreas Färber wrote:
> 
> > Am 20.05.2011 um 09:40 schrieb Alexander Graf:
> > 
> >> On 20.05.2011, at 05:34, David Gibson wrote:
> >> 
> >>> Early ppc64 CPUs include a hack to partially simulate the ppc32 segment
> >>> registers, by translating writes to them into writes to the SLB.  This is
> >>> not used by any current Linux kernel, but it is used by the openbios used
> >>> in the qemu mac99 model.
> >>> 
> >>> Commit 81762d6dd0d430d87024f2c83e9c4dcc4329fb7d, cleaning up the SLB
> >>> handling introduced a bug in this code, breaking the openbios currently in
> >>> qemu.  Specifically, there was an off by one error bitshuffling the
> >>> register format used by mtsr into the format needed for the SLB load,
> >>> causing the flag bits to end up in the wrong place.  This caused the
> >>> storage keys to be wrong under openbios, meaning that the translation code
> >>> incorrectly thought a legitimate access was a permission violation.
> >>> 
> >>> This patch fixes the bug, at the same time it fixes some build bug in the
> >>> MMU debugging code (only exposed when DEBUG_MMU is enabled).
> >> 
> >> Thanks, applied to ppc-next :)
> > 
> > Hm. Don't you think we should split off the unrelated debug code fix for bisecting?
> 
> Not sure if it's worth the effort. If you were bisecting before
> that, you probably had DEBUG_MMU disabled anyways, because you'd
> otherwise get build breakages before that specific commit anyways,
> so the commit behaves as if it's only the SLB fix.

Right, I don't see how the debug fixes break bisect in any way.  Or
least not in any way they werem't already broken.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
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