linux-kernel - Re: [PATCH 1/3] jump_label: Add annotations for validating noinstr usage

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Message-ID: <20241123015407.vvdgcr4pd7hyx7c2@jpoimboe>
Date: Fri, 22 Nov 2024 17:54:07 -0800
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Valentin Schneider <vschneid@...hat.com>
Cc: linux-kernel@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 1/3] jump_label: Add annotations for validating noinstr
 usage

On Fri, Nov 22, 2024 at 05:52:20PM -0800, Josh Poimboeuf wrote:
> Deferring a code patching IPI is unsafe if the patched code is in a
> noinstr region.  In that case the text poke code must trigger an
> immediate IPI to all CPUs, which can rudely interrupt an isolated NO_HZ
> CPU running in userspace.
> 
> Some noinstr static branches may really need to be patched at runtime,
> despite the resulting disruption.  Add DEFINE_STATIC_KEY_*_NOINSTR()
> variants for those.  They don't do anything special yet; that will come
> later.
> 
> Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>

Oops, $SUBJECT should probably be changed to something like:

jump_label: Add DEFINE_STATIC_KEY_*_NOINSTR()

-- 
Josh