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

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Message-ID: <20150224102545.GD19976@gmail.com>
Date:	Tue, 24 Feb 2015 11:25:45 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Pavel Machek <pavel@....cz>
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)


* Pavel Machek <pavel@....cz> wrote:

> > 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.

That should be OK, as a new kernel will be ABI compatible 
with an old kernel.

A later optimization could update the glibc cache on an 
upgrade, fortunately both projects are open source.

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

That should be fine too.

Thanks,

	Ingo
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