linux-kernel - Re: [PATCH] ARM: ftrace: Ensure code modifications are synchronised across all cpus

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Date:	Mon, 10 Dec 2012 11:04:05 +0000
From:	"Jon Medhurst (Tixy)" <tixy@...aro.org>
To:	Will Deacon <will.deacon@....com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Rabin Vincent <rabin@....in>, Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] ARM: ftrace: Ensure code modifications are synchronised
 across all cpus

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

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