linux-kernel - Re: [PATCH] livepatch: Remove klp_arch_set

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Date:   Mon, 28 Mar 2022 12:23:42 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Petr Mladek <pmladek@...e.com>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
        live-patching@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-s390@...r.kernel.org, x86@...nel.org,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH] livepatch: Remove klp_arch_set_pc() and asm/livepatch.h

On Mon, Mar 28, 2022 at 08:26:48AM +0200, Christophe Leroy wrote:
> All three versions of klp_arch_set_pc() do exactly the same: they
> call ftrace_instruction_pointer_set().
> 
> Call ftrace_instruction_pointer_set() directly and remove
> klp_arch_set_pc().
> 
> As klp_arch_set_pc() was the only thing remaining in asm/livepatch.h
> on x86 and s390, remove asm/livepatch.h
> 
> livepatch.h remains on powerpc but its content is exclusively used
> by powerpc specific code.

The only remaining thing seems to be a klp_init_thread_info() for ppc64,
but yeah..

Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>

> diff --git a/kernel/livepatch/patch.c b/kernel/livepatch/patch.c
> index c172bf92b576..4c4f5a776d80 100644
> --- a/kernel/livepatch/patch.c
> +++ b/kernel/livepatch/patch.c
> @@ -118,7 +118,7 @@ static void notrace klp_ftrace_handler(unsigned long ip,
>  	if (func->nop)
>  		goto unlock;
>  
> -	klp_arch_set_pc(fregs, (unsigned long)func->new_func);
> +	ftrace_instruction_pointer_set(fregs, (unsigned long)func->new_func);
>  
>  unlock:
>  	ftrace_test_recursion_unlock(bit);

So ptrace has instruction_pointer_set(), I'm not sure why we have yet
another variant in the ftrace_ namespace. Perhaps also delete that?