Date: Mon, 23 Feb 2015 12:39:33 +0100
From: Pavel Machek <pavel@ucw.cz>
To: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Kosina <jkosina@suse.cz>, Vojtech Pavlik <vojtech@suse.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Ingo Molnar <mingo@redhat.com>, Seth Jennings <sjenning@redhat.com>,
        linux-kernel@vger.kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Arjan van de Ven <arjan@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Borislav Petkov <bp@alien8.de>
Subject: Re: live kernel upgrades (was: live kernel patching design)
Message-ID: <20150223113908.GA3206@Nokia-N900>
References: <20150220194901.GB3603@gmail.com>
 <20150220214613.GA21598@suse.com>
 <20150221181852.GA8406@gmail.com>
 <alpine.LNX.2.00.1502211952120.2357@pobox.suse.cz>
 <20150221191607.GA9534@gmail.com>
 <alpine.LNX.2.00.1502212025450.2357@pobox.suse.cz>
 <20150221194840.GA10126@gmail.com>
 <alpine.LNX.2.00.1502212058080.2357@pobox.suse.cz>
 <20150222084601.GA23491@gmail.com>
 <20150222094639.GA23684@gmail.com>
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> 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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