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Subject: Re: [PATCH v2 11/25] powerpc/8xx: map 16M RAM at startup
From: Scott Wood <scottwood@freescale.com>
To: Christophe Leroy <christophe.leroy@c-s.fr>
CC: Benjamin Herrenschmidt <benh@kernel.crashing.org>, Paul Mackerras
 <paulus@samba.org>, Michael Ellerman <mpe@ellerman.id.au>,
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Date: Tue, 6 Oct 2015 10:17:28 -0500
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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@c-s.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