linux-kernel - Re: [PATCH] powerpc 8xx: Loading kernels over 8Mbytes without CONFIG_PIN

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Message-ID: <1386449914.21910.109.camel@pasglop>
Date:	Sun, 08 Dec 2013 07:58:34 +1100
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	christophe leroy <christophe.leroy@....fr>
Cc:	Scott Wood <scottwood@...escale.com>,
	Paul Mackerras <paulus@...ba.org>,
	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH] powerpc 8xx: Loading kernels over 8Mbytes without
 CONFIG_PIN_TLB

On Sat, 2013-12-07 at 10:39 +0100, christophe leroy wrote:
> Function setup_initial_memory_limit() in mm/init_32.c defines the
> limits 
> based on the parameters given by the bootloader.
> As far as I know, the 8xx doesn't do speculative access just because
> an area is loaded in a TLB Entry.

Speculative accesses are ... speculative :-) The address used for such
an access can be anything really. So yes, architecturally, powerpc
processors can access *anything* speculatively just because there's a
valid non-garded translation.

Whether the 8xx does it at all, I don't know. 44x originally did but
that was so buggy that we had to force G on all mappings (until later
versions of the core just burned the feature out). Pretty much all other
powerpc's do it.

Cheers,
Ben.

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