linux-kernel - Re: [PATCH] powerpc: Fix alignment of secondary cpu spin vars

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Message-ID: <1389154189.2076.5.camel@concordia>
Date:	Wed, 08 Jan 2014 15:09:49 +1100
From:	Michael Ellerman <michael@...erman.id.au>
To:	Olof Johansson <olof@...om.net>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	chzigotzky@...osoft.de,
	linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Anton Blanchard <anton@...ba.org>
Subject: Re: [PATCH] powerpc: Fix alignment of secondary cpu spin vars

On Fri, 2014-01-03 at 00:12 -0800, Olof Johansson wrote:
> On Thu, Jan 02, 2014 at 11:56:04PM -0800, Olof Johansson wrote:
> 
> > This makes things interesting though. The BE/LE trampoline code
> > assumes at least 3 consecutive instructions. What was the reasoning
> > behind entering the kernel LE instead of keeping the old boot protocol
> > and just switching to LE once kernel is loaded? Is it actually used on
> > some platforms or is this just a theoretical thing?
> 
> Actually, adding a little hack that zeroes out the memory once we're done
> executing it will work just fine too. I know this is sort of icky, but maybe
> it'll be good enough for now?
> 
> Of course, main worry is that this is just hiding some latent NULL deref in
> the kernel now... :-/

Wow, that would have to come close to winning the grossest-hack-in-arch-powerpc
award :)

Have you tried changing the value at 8 to point to a reserved page?

Some other possibilities:

 * Change the #define so FIXUP_ENDIAN is empty for PASEMI, that would mean
   you'd only be able to boot pasemi_defconfig.
 * Move the hack into FIXUP_ENDIAN

cheers


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