linux-kernel - Re: Bug with paravirt ops and livepatches

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Message-ID: <alpine.LNX.2.00.1603291504010.3656@cbobk.fhfr.pm>
Date:	Tue, 29 Mar 2016 15:05:34 +0200 (CEST)
From:	Jiri Kosina <jikos@...nel.org>
To:	Miroslav Benes <mbenes@...e.cz>
cc:	Chris J Arges <chris.j.arges@...onical.com>, jeyu@...hat.com,
	jpoimboe@...hat.com, eugene.shatokhin@...alab.ru,
	live-patching@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	pmladek@...e.cz
Subject: Re: Bug with paravirt ops and livepatches

On Tue, 29 Mar 2016, Miroslav Benes wrote:

> > 1) Jessica proposed using the Arch-independent patchset ensure that livepatch
> > finishes writing its relas before apply_paravirt() is called. However, this
> > introduces a bit more arch-dependent code. It would be useful to see if other
> > arches are affected by this as well.
> 
> I think this is the way to go. Provided we have Jessica's two patch sets 
> applied (arch-independent and notifiers removal) there are two options. We 
> either move a call to klp_coming_module() somewhere before 
> module_finalize(), or we move the problematic parts of module_finalize() 
> to the end of load_module() (on x86 it is probably module_finalize() as a 
> whole). The former is almost impossible because of the dependencies 
> (ftrace and such), the latter should be doable (with very careful check we 
> won't break anything).

Agreed; I think we should be safe applying all the alternatives (with 
paravirt being really just a special case of those) to the coming module 
at the very last phase; they really are required only during runtime, but 
nothing else should be depending on them. Right? If anyone is able to come 
up with and counter-example, please speak up :)

Thanks,

-- 
Jiri Kosina
SUSE Labs