linux-kernel - Re: Re: [RFC] [PATCH 1/2 v2] x86: introduce int3-based instruction patching

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Message-ID: <51DE2698.3060307@hitachi.com>
Date:	Thu, 11 Jul 2013 12:29:28 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	"H. Peter Anvin" <hpa@...ux.intel.com>
Cc:	Jiri Kosina <jkosina@...e.cz>,
	Steven Rostedt <rostedt@...dmis.org>,
	Jason Baron <jbaron@...hat.com>,
	Borislav Petkov <bpetkov@...e.de>, linux-kernel@...r.kernel.org
Subject: Re: Re: [RFC] [PATCH 1/2 v2] x86: introduce int3-based instruction
 patching

(2013/07/11 6:36), H. Peter Anvin wrote:
> On 07/10/2013 02:31 PM, Jiri Kosina wrote:
>>
>> If any CPU instruction execution would collide with the patching,
>> it'd be trapped by the int3 breakpoint and redirected to the provided
>> "handler" (which would typically mean just skipping over the patched
>> region, acting as "nop" has been there, in case we are doing nop -> jump
>> and jump -> nop transitions).
>>
> 
> I'm wondering if it would be easier/more general to just return to the
> instruction.  The "more general" bit would allow this to be used for
> other things, like alternatives, and perhaps eventually dynamic call
> patching.
>
> Returning to the instruction will, in effect, be a busy-wait for the
> faulted CPU until the patch is complete; more or less what stop_machine
> would do, but only for a CPU which actually strays into the affected region.

Sounds a good idea :)
It may minimize the interface and the implementation will be
self-contained.

Thank you,

-- 
Masami HIRAMATSU
IT Management Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@...achi.com


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