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Message-ID: <1355137445.3386.7.camel@linaro1.home>
Subject: Re: [PATCH] ARM: ftrace: Ensure code modifications are synchronised
 across all cpus
From: "Jon Medhurst (Tixy)" <tixy@linaro.org>
To: Will Deacon <will.deacon@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>,
        Russell King - ARM Linux <linux@arm.linux.org.uk>,
        Frederic Weisbecker <fweisbec@gmail.com>,
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        Rabin Vincent <rabin@rab.in>, Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@linux.intel.com>,
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	<linux-arm-kernel@lists.infradead.org>
Date: Mon, 10 Dec 2012 11:04:05 +0000
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On Fri, 2012-12-07 at 19:02 +0000, Will Deacon wrote:
> For ARMv7, there are small subsets of instructions for ARM and Thumb which
> are guaranteed to be atomic wrt concurrent modification and execution of
> the instruction stream between different processors:
> 
> Thumb:	The 16-bit encodings of the B, NOP, BKPT, and SVC instructions.
> ARM:	The B, BL, NOP, BKPT, SVC, HVC, and SMC instructions.
> 

So this means for things like kprobes which can modify arbitrary kernel
code we are going to need to continue to always use some form of
stop_the_whole_system() function?

Also, kprobes currently uses patch_text() which only uses stop_machine
for Thumb2 instructions which straddle a word boundary, so this needs
changing?

-- 
Tixy