Re: [RFC patch] Immediate Values - x86 Optimization NMI and MCE support

From: Masami Hiramatsu <mhiramat@redhat.com>
To: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Cc: Peter Zijlstra <peterz@infradead.org>,
	anil.s.keshavamurthy@intel.com, Jason Yeh <jason.yeh@amd.com>,
	Robert Richter <robert.richter@amd.com>,
	Andi Kleen <andi@firstfloor.org>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Chuck Ebbert <cebbert@redhat.com>,
	Christoph Hellwig <hch@infradead.org>,
	Jeremy Fitzhardinge <jeremy@goop.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Ingo Molnar <mingo@elte.hu>,
	linux-kernel@vger.kernel.org,
	"Frank Ch. Eigler" <fche@redhat.com>,
	Hideo AOKI <haoki@redhat.com>,
	Takashi Nishiie <t-nishiie@np.css.fujitsu.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Subject: Re: [RFC patch] Immediate Values - x86 Optimization NMI and MCE support
Date: Thu, 24 Sep 2009 14:59:27 -0700	[thread overview]
Message-ID: <4ABBEBBF.9080400@redhat.com> (raw)
In-Reply-To: <20090924160118.GA28846@Krystal>

Mathieu Desnoyers wrote:
> [Ingo: this patch is for RFC only. Do not merge.]
> 
> * Peter Zijlstra (peterz@infradead.org) wrote:
>> On Thu, 2009-09-24 at 11:03 -0400, Mathieu Desnoyers wrote:
>>> * Peter Zijlstra (peterz@infradead.org) wrote:
>>>> On Thu, 2009-09-24 at 09:26 -0400, Mathieu Desnoyers wrote:
>>>>> plain text document attachment (tracepoints-immediate-values.patch)
>>>>> Use immediate values in tracepoints.
>>>>
>>>> I might have missed it, but did both the Intel and AMD cpu folks clear
>>>> the SMP code rewrite bits?
>>>>
>>>
>>> SMP handling is performed with stop_machine() in this patchset. Nothing
>>> fancy here.
>>>
>>> I've got other patches, not included in this patchset, which implements
>>> nmi-safe code modification, based on a scheme using breakpoints and
>>> IPIs, inspired from djprobes. That one might be worth clearing with
>>> intel/amd devs before merging.
>>>
>>> However, doing code patching within stop_machine() is pretty safe, given
>>> all other CPUs are busy-looping with interrupts off while this happens.
>>> Ftrace already does this.
>>
>> Agreed, I missed this relied on stopmachine. No problem then.
>>
>> It would be good to reduce reliance on stopmachine, so it would be good
>> to get some CPU folks looking at your alternative implementation.
>>
>> Thanks!
>>
> 
> Sure, here is the patch applying on top of the immediate values
> patchset. It implements the breakpoint-based instruction patching
> scheme. I just provide this one for review. There is a following patch
> which makes the immediate values infrastructure use this arch-specific
> file, which I'll leave out for now.

Mathieu, could you check my previous patch?
http://lkml.org/lkml/2009/9/14/551

I think we can share some code and ideas about generic XMC:-).
But since it seems that the imv requires a dedicated method,
I don't think we can share the code entirely. :-)

> +#include <asm/cacheflush.h>
> +
> +#define BREAKPOINT_INSTRUCTION  0xcc
> +#define BREAKPOINT_INS_LEN	1
> +#define NR_NOPS			10

Why don't you reuse macros in asm/include/kprobes.h? :)

Thank you,

-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America), Inc.
Software Solutions Division

e-mail: mhiramat@redhat.com