linux-kernel - Re: [PATCH v3 5/6] x86/ftrace: Use text

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Message-ID: <alpine.LSU.2.21.1910161216100.7750@pobox.suse.cz>
Date:   Wed, 16 Oct 2019 12:20:36 +0200 (CEST)
From:   Miroslav Benes <mbenes@...e.cz>
To:     Peter Zijlstra <peterz@...radead.org>
cc:     Steven Rostedt <rostedt@...dmis.org>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Jessica Yu <jeyu@...nel.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org, mhiramat@...nel.org,
        bristot@...hat.com, jbaron@...mai.com,
        torvalds@...ux-foundation.org, tglx@...utronix.de,
        mingo@...nel.org, namit@...are.com, hpa@...or.com, luto@...nel.org,
        ard.biesheuvel@...aro.org, jpoimboe@...hat.com,
        live-patching@...r.kernel.org, pmladek@...e.com
Subject: Re: [PATCH v3 5/6] x86/ftrace: Use text_poke()

On Wed, 16 Oct 2019, Peter Zijlstra wrote:

> On Tue, Oct 15, 2019 at 06:27:05PM -0400, Steven Rostedt wrote:
> 
> > (7) Seventh session, titled "klp-convert and livepatch relocations", was led
> > by Joe Lawrence.
> > 
> > Joe started the session with problem statement: accessing non exported / static
> > symbols from inside the patch module. One possible workardound is manually via
> > kallsyms. Second workaround is klp-convert, which actually creates proper
> > relocations inside the livepatch module from the symbol database during the
> > final .ko link.
> > Currently module loader looks for special livepatch relocations and resolves
> > those during runtime; kernel support for these relocations have so far been
> > added for x86 only. Special livepatch relocations are supported and processed
> > also on other architectures. Special quirks/sections are not yet supported.
> > Plus klp-convert would still be needed even with late module patching update.
> > vmlinux or modules could have ambiguous static symbols.
> > 
> > It turns out that the features / bugs below have to be resolved before we
> > can claim the klp-convert support for relocation complete:
> >     - handle all the corner cases (jump labels, static keys, ...) properly and
> >       have a good regression tests in place
> 
> I suppose all the patches in this series-of-series here will make life
> harder for KLP, static_call() and 2 byte jumps etc..

Yes, I think so. We'll have to deal with that once it lands. That is why 
we want to get rid of all this arch-specific code in livepatch and 
reinvent the late module patching. So it is perhaps better to start 
working on it sooner than later. Adding Petr, who hesitantly signed up for 
the task...

Miroslav