linux-kernel - Re: [PATCHv4 0/3] Kernel Live Patching

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Date:	Thu, 27 Nov 2014 15:12:50 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Jiri Kosina <jkosina@...e.cz>
Cc:	Seth Jennings <sjenning@...hat.com>,
	Josh Poimboeuf <jpoimboe@...hat.com>,
	Vojtech Pavlik <vojtech@...e.cz>,
	Steven Rostedt <rostedt@...dmis.org>,
	Petr Mladek <pmladek@...e.cz>, Miroslav Benes <mbenes@...e.cz>,
	Christoph Hellwig <hch@...radead.org>,
	Greg KH <gregkh@...uxfoundation.org>,
	Andy Lutomirski <luto@...capital.net>,
	live-patching@...r.kernel.org, x86@...nel.org, kpatch@...hat.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCHv4 0/3] Kernel Live Patching

(2014/11/26 18:18), Jiri Kosina wrote:
> On Wed, 26 Nov 2014, Masami Hiramatsu wrote:
> 
>>> Note to Steve:
>>> Masami's IPMODIFY patch is heading for -next via your tree.  Once it arrives,
>>> I'll rebase and make the change to set IPMODIFY.  Do not pull this for -next
>>> yet.  This version (v4) is for review and gathering acks.
>>
>> BTW, as we discussed IPMODIFY is an exclusive flag. So if we allocate 
>> ftrace_ops for each function in each patch, it could be conflict each 
>> other.
> 
> Yup, this corresponds to what Petr brought up yesterday. There are cases 
> where all solutions (kpatch, kgraft, klp) would allocate multiple 
> ftrace_ops for a single function entry (think of patching one function 
> multiple times in a row).
> 
> So it's not as easy as just setting the flag.
> 
>> Maybe we need to have another ops hashtable to find such conflict and 
>> new handler to handle it.
> 
> If I understand your proposal correctly, that would sound like a hackish 
> workaround, trying to basically trick the IPMODIFY flag semantics you just 
> implemented :)
> 
> What I'd propose instead is to make sure that we always have 
> just a ftrace_ops per function entry, and only update the pointers there 
> as necessary. Fortunately we can do the switch atomically, by making use 
> of ->private.

Would you mean per existing function entry, not per klp-func entry?
If so, it sounds good to me too :)

Thank you,


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


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