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Date: Sat, 28 Feb 2009 23:08:29 +0100
From: Pavel Machek <pavel@ucw.cz>
To: Andi Kleen <andi@firstfloor.org>
Cc: Steven Rostedt <rostedt@goodmis.org>, linux-kernel@vger.kernel.org,
       Ingo Molnar <mingo@elte.hu>, Andrew Morton <akpm@linux-foundation.org>,
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       Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>,
       "H. Peter Anvin" <hpa@zytor.com>, Steven Rostedt <srostedt@redhat.com>
Subject: Re: [PATCH 4/6] ftrace, x86: make kernel text writable only for
	conversions
Message-ID: <20090228220829.GE21230@elf.ucw.cz>
References: <20090220011316.379904625@goodmis.org> <20090220011521.003556651@goodmis.org> <87y6vyuzsn.fsf@basil.nowhere.org> <20090227210856.GB1476@ucw.cz> <20090228165624.GC26292@one.firstfloor.org>
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> > > The very old text poke code I had for this just used a dynamic
> > > mapping elsewhere instead to modify the code. That's much less
> > > intrusive than changing the complete mappings. Any reason you can't use 
> > > that too?
> > 
> > Is it legal to have two mappings of same page with different
> > attributes? IIRC some processors did not like that...
> 
> If you mean PAT caching attributes: correct it is not legal in x86 and
> causes problems including data corruption.

Aha, PAT is what I remembered on x86-64.

> If you mean other attributes like large page vs small page: it's normally legal,
> with a few exceptions.

...but is it okay on other architectures, like sparc, with funky cache
setups?
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
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