linux-kernel - Re: [PATCH v2 09/13] powerpc/ftrace: Implement CONFIG_DYNAMIC_FTRACE_WITH

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Message-ID: <alpine.LSU.2.21.2112221515020.18494@pobox.suse.cz>
Date:   Wed, 22 Dec 2021 15:19:20 +0100 (CET)
From:   Miroslav Benes <mbenes@...e.cz>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
cc:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Jiri Kosina <jikos@...nel.org>, Petr Mladek <pmladek@...e.com>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        "Naveen N . Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "live-patching@...r.kernel.org" <live-patching@...r.kernel.org>,
        linux-arm-kernel@...ts.infradead.org, mark.rutland@....com,
        broonie@...nel.org, madvenka@...ux.microsoft.com
Subject: Re: [PATCH v2 09/13] powerpc/ftrace: Implement
 CONFIG_DYNAMIC_FTRACE_WITH_ARGS

On Mon, 20 Dec 2021, Christophe Leroy wrote:

> Implement CONFIG_DYNAMIC_FTRACE_WITH_ARGS. It accelerates the call
> of livepatching.
> 
> Also note that powerpc being the last one to convert to
> CONFIG_DYNAMIC_FTRACE_WITH_ARGS, it will now be possible to remove
> klp_arch_set_pc() on all architectures.

Correct. We could replace it ftrace_instruction_pointer_set() and that is 
it. In fact, livepatch.h in both arch/x86/include/asm/ and 
arch/s390/include/asm/ could be removed with that.

On the other hand, there is arm64 live patching support being worked on 
and I am not sure what their plans about DYNAMIC_FTRACE_WITH_ARGS are. The 
above would make it a prerequisite.

Adding CCs... you can find the whole thread at 
https://lore.kernel.org/all/cover.1640017960.git.christophe.leroy@csgroup.eu/

Miroslav