linux-kernel - Re: [PATCH v3 2/2] livepatch: add atomic replace

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Date:   Tue, 17 Oct 2017 16:27:00 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Miroslav Benes <mbenes@...e.cz>
Cc:     Jason Baron <jbaron@...mai.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        linux-kernel@...r.kernel.org, live-patching@...r.kernel.org,
        jeyu@...nel.org, jikos@...nel.org
Subject: Re: [PATCH v3 2/2] livepatch: add atomic replace

On Tue 2017-10-17 11:02:29, Miroslav Benes wrote:
> On Tue, 10 Oct 2017, Jason Baron wrote:
> > On 10/06/2017 06:32 PM, Josh Poimboeuf wrote:
> > > I don't really like allowing a previously replaced patch to replace the
> > > current patch.  It's just more unnecessary complexity.

I am sorry to say but it really makes the code too complex.

> > > If the user
> > > wants to atomically revert back to kpatch-a, they should be able to:
> > > 
> > >   rmmod kpatch-a
> > >   insmod kpatch-a.ko
> > >
> > Right - that's how I sent v1 (using rmmod/insmod to revert), but it
> > didn't account for the fact the patch or some functions may be marked
> > 'immediate' and thus its not possible to just do 'rmmod'. Thus, since in
> > some cases 'rmmod' was not feasible, I thought it would be simpler from
> > an operational pov to just say we always revert by re-enabling a
> > previously replaced patch as opposed to rmmod/insmod.
> > 
> Hm. Would it make sense to remove immediate and rely only on the 
> consistency model? At least for the architectures where the model is 
> implemented (x86_64)?
> 
> If not, then I'd keep such modules there without a possibility to remove 
> them ever. If its functionality was required again, it would of course 
> mean to insmod a new module with it.

I am fine with this compromise. It seems to be the only way to keep the
livepatch code somehow sane.

Best Regards,
Petr