linux-kernel - Re: live kernel upgrades (was: live kernel patching design)

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Date:	Mon, 23 Feb 2015 12:39:33 +0100
From:	Pavel Machek <pavel@....cz>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Jiri Kosina <jkosina@...e.cz>, Vojtech Pavlik <vojtech@...e.com>,
	Josh Poimboeuf <jpoimboe@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...hat.com>,
	Seth Jennings <sjenning@...hat.com>,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Borislav Petkov <bp@...en8.de>
Subject: Re: live kernel upgrades (was: live kernel patching design)

> More importantly, both kGraft and kpatch are pretty limited 
> in what kinds of updates they allow, and neither kGraft nor 
> kpatch has any clear path towards applying more complex 
> fixes to kernel images that I can see: kGraft can only 
> apply the simplest of fixes where both versions of a 
> function are interchangeable, and kpatch is only marginally 
> better at that - and that's pretty fundamental to both 
> projects!
> 
> I think all of these problems could be resolved by shooting 
> for the moon instead:
> 
>   - work towards allowing arbitrary live kernel upgrades!
> 
> not just 'live kernel patches'.

Note that live kernel upgrade would have interesting implications
outside kernel:

1) glibc does "what kernel version is this?" caches result
and alters behaviour accordingly.

2) apps will do recently_introduced_syscall(), get error 
and not attempt it again.

						Pavel
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