linux-kernel - Re: [PATCH 20/22] x86,word-at-a-time: Remove .fixup usage

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Message-ID: <20211115230327.m3zswzgrshotocju@treble>
Date:   Mon, 15 Nov 2021 15:40:11 -0800
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Joe Lawrence <joe.lawrence@...hat.com>
Cc:     Miroslav Benes <mbenes@...e.cz>,
        Peter Zijlstra <peterz@...radead.org>,
        David Laight <David.Laight@...lab.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Bill Wendling <morbo@...gle.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "dvyukov@...gle.com" <dvyukov@...gle.com>,
        "seanjc@...gle.com" <seanjc@...gle.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "llvm@...ts.linux.dev" <llvm@...ts.linux.dev>,
        "linux-toolchains@...r.kernel.org" <linux-toolchains@...r.kernel.org>,
        live-patching@...r.kernel.org
Subject: Re: [PATCH 20/22] x86,word-at-a-time: Remove .fixup usage

On Mon, Nov 15, 2021 at 08:01:13AM -0500, Joe Lawrence wrote:
> > This reminded me... one of the things I have on my todo list for a long 
> > time is to add an option for a live patch creator to specify functions 
> > which are not contained in the live patch but their presence on stacks 
> > should be checked for. It could save some space in the final live patch 
> > when one would add functions (callers) just because the consistency 
> > requires it.
> > 
> 
> Yea, I've used this technique once (adding a nop to a function so
> kpatch-build would detect and include in klp_funcs[]) to make a set of
> changes safer with respect to the consistency model.  Making it simpler
> to for the livepatch author to say, "I'm not changing foo(), but I don't
> want it doing anything while patching a task" sounds reasonable.
> 
> > I took as a convenience feature with a low priority and forgot about it. 
> > The problem above changes it. So should we take the opportunity and 
> > implement both in one step? I wanted to include a list of functions in 
> > on a patch level (klp_patch structure) and klp_check_stack() would just 
> > have more to check.
> > 
> 
> As far as I read the original problem, I think it would solve for that,
> too, so I would say go for it.

Sounds good to me.

Miroslav, do I understand correctly that you're volunteering to make
this change? ;-)

-- 
Josh