linux-kernel - Re: [PATCH] x86/alternative: Consistently patch SMP locks in vmlinux and modules

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Date:   Thu, 27 Oct 2022 08:55:22 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Julian Pidancet <julian.pidancet@...cle.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH] x86/alternative: Consistently patch SMP locks in vmlinux
 and modules

On Tue, Aug 30, 2022 at 09:42:37AM +0200, Julian Pidancet wrote:
> The alternatives_smp_module_add() function restricts patching of SMP
> lock prefixes to the text address range passed as an argument.
> 
> For vmlinux, patching all the instructions located between the _text and
> _etext symbols is allowed. That includes the .text section but also
> other sections such as .text.hot and .text.unlikely.
> 
> As per the comment inside the 'struct smp_alt_module' definition, the
> original purpose of this restriction is to avoid patching the init code
> which may have been deallocated when the alternatives code run.

It is not; init code is still around when we run alternatives.