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

From: Miroslav Benes <mbenes@suse.cz>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Joe Lawrence <joe.lawrence@redhat.com>,
	 Peter Zijlstra <peterz@infradead.org>,
	 David Laight <David.Laight@aculab.com>,
	 Nick Desaulniers <ndesaulniers@google.com>,
	 Bill Wendling <morbo@google.com>,
	"x86@kernel.org" <x86@kernel.org>,
	 "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	 "mark.rutland@arm.com" <mark.rutland@arm.com>,
	 "dvyukov@google.com" <dvyukov@google.com>,
	 "seanjc@google.com" <seanjc@google.com>,
	 "pbonzini@redhat.com" <pbonzini@redhat.com>,
	 "llvm@lists.linux.dev" <llvm@lists.linux.dev>,
	 "linux-toolchains@vger.kernel.org"
	<linux-toolchains@vger.kernel.org>,
	 live-patching@vger.kernel.org
Subject: Re: [PATCH 20/22] x86,word-at-a-time: Remove .fixup usage
Date: Tue, 16 Nov 2021 08:25:31 +0100 (CET)	[thread overview]
Message-ID: <alpine.LSU.2.21.2111160823350.2250@pobox.suse.cz> (raw)
In-Reply-To: <20211115230327.m3zswzgrshotocju@treble>

On Mon, 15 Nov 2021, Josh Poimboeuf wrote:

> 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? ;-)

Yes, you do. I am not superfast peterz, so it will take some time, but 
I'll be happy to do it :).

Miroslav