linux-kernel - Re: [PATCH v2 11/25] powerpc/8xx: map 16M RAM at startup

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Message-ID: <1444144648.5336.271.camel@freescale.com>
Date:	Tue, 6 Oct 2015 10:17:28 -0500
From:	Scott Wood <scottwood@...escale.com>
To:	Christophe Leroy <christophe.leroy@....fr>
CC:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	<linux-kernel@...r.kernel.org>, <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH v2 11/25] powerpc/8xx: map 16M RAM at startup

On Tue, 2015-10-06 at 16:10 +0200, Christophe Leroy wrote:
> Le 29/09/2015 01:58, Scott Wood a écrit :
> > On Tue, Sep 22, 2015 at 06:50:50PM +0200, Christophe Leroy wrote:
> > > On recent kernels, with some debug options like for instance
> > > CONFIG_LOCKDEP, the BSS requires more than 8M memory, allthough
> > > the kernel code fits in the first 8M.
> > > Today, it is necessary to activate CONFIG_PIN_TLB to get more than 8M
> > > at startup, allthough pinning TLB is not necessary for that.
> > > 
> > > This patch adds a second 8M page to the initial mapping in order to
> > > have 16M mapped regardless of CONFIG_PIN_TLB, like several other
> > > 32 bits PPC (40x, 601, ...)
> > > 
> > > Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
> > > ---
> > Is the assumption that nobody is still running 8xx systems with only 8
> > MiB RAM on current kernels?
> > 
> > 
> No, setup_initial_memory_limit() limits the memory to the minimum 
> between 16M and the real memory size, so if a platform has only 8M, it 
> will still be limited to 8M even with 16M mapped.

And you just hope you don't get a speculative fetch from the second 8M?

-Scott

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