linux-kernel - Re: [PATCH 4/6] ftrace, x86: make kernel text writable only for conversions

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Message-ID: <20090228220829.GE21230@elf.ucw.cz>
Date:	Sat, 28 Feb 2009 23:08:29 +0100
From:	Pavel Machek <pavel@....cz>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	"H. Peter Anvin" <hpa@...or.com>,
	Steven Rostedt <srostedt@...hat.com>
Subject: Re: [PATCH 4/6] ftrace, x86: make kernel text writable only for
	conversions

> > > 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
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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