From: Ingo Molnar <mingo@elte.hu>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: linux-kernel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
Peter Zijlstra <peterz@infradead.org>,
Steven Rostedt <srostedt@redhat.com>
Subject: Re: [PATCH 2/5] ftrace, x86: make kernel text writable only for conversions
Date: Fri, 20 Feb 2009 18:55:35 +0100 [thread overview]
Message-ID: <20090220175535.GN24538@elte.hu> (raw)
In-Reply-To: <alpine.DEB.2.00.0902201247220.13747@gandalf.stny.rr.com>
* Steven Rostedt <rostedt@goodmis.org> wrote:
> > > +/* used by ftrace */
> > > +void set_kernel_text_rw(void)
> >
> > i'd leave out the 'used by ftrace' bit - more uses might
> > arise. How does kprobes get around readonly pages, it uses
> > these APIs too, right?
>
> kprobes uses text_poke. text_poke uses vmap to create its own
> page table pointers to the text memory, does the modification
> and then removes the pointers. This is quite heavy weight and
> since ftrace needs to modify 10s of thousands of areas,
> converting all of kernel text page tables is much more
> efficient.
>
> Note, if kprobes did change the original page tables, then it
> too would have hit the split_large_page bug too.
i think the real reason is that kprobes was written before we
had this more flexible and more usable CPA code.
Ingo
next prev parent reply other threads:[~2009-02-20 17:56 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-02-20 16:38 [git pull] updates for tip Steven Rostedt
2009-02-20 16:38 ` [PATCH 1/5] ftrace: allow archs to preform pre and post process for code modification Steven Rostedt
2009-02-20 17:25 ` Ingo Molnar
2009-02-20 17:32 ` Steven Rostedt
2009-02-20 16:38 ` [PATCH 2/5] ftrace, x86: make kernel text writable only for conversions Steven Rostedt
2009-02-20 17:30 ` Ingo Molnar
2009-02-20 17:52 ` Steven Rostedt
2009-02-20 17:55 ` Ingo Molnar [this message]
2009-02-20 18:00 ` Steven Rostedt
2009-02-20 16:38 ` [PATCH 3/5] ftrace: immediately stop code modification if failure is detected Steven Rostedt
2009-02-20 16:38 ` [PATCH 4/5] ftrace: break out modify loop immediately on detection of error Steven Rostedt
2009-02-20 17:33 ` Ingo Molnar
2009-02-20 17:54 ` Steven Rostedt
2009-02-20 16:38 ` [PATCH 5/5] ftrace, x86: do not depend on system state for kernel text info Steven Rostedt
2009-02-20 17:34 ` Ingo Molnar
2009-02-20 17:54 ` Steven Rostedt
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