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Date: Mon, 15 Mar 2021 10:28:23 -0700
From: Kees Cook <>
To: Andrew Morton <>
Cc: Thomas Gleixner <>,,
	Elena Reshetova <>,,
	Andy Lutomirski <>,
	Peter Zijlstra <>,
	Catalin Marinas <>,
	Will Deacon <>, Mark Rutland <>,
	Alexander Potapenko <>,
	Alexander Popov <>,
	Ard Biesheuvel <>,
	Jann Horn <>,,,,,, Vlastimil Babka <>,
	David Hildenbrand <>,
	Mike Rapoport <>,
	Jonathan Corbet <>,
	Randy Dunlap <>
Subject: Re: [PATCH v5 1/7] mm: Restore init_on_* static branch defaults

On Wed, Mar 10, 2021 at 03:56:02PM -0800, Andrew Morton wrote:
> On Tue,  9 Mar 2021 13:42:55 -0800 Kees Cook <> wrote:
> > Choosing the initial state of static branches changes the assembly layout
> > (if the condition is expected to be likely, inline, or unlikely, out of
> > line via a jump). The _TRUE/_FALSE defines for CONFIG_INIT_ON_*_DEFAULT_ON
> > were accidentally removed. These need to stay so that the CONFIG controls
> > the pessimization of the resulting static branch NOP/JMP locations.
> Changelog doesn't really explain why anyone would want to apply this
> patch.  This is especially important for -stable patches.
> IOW, what is the user visible effect of the bug?

Yeah, that's a good point, and in writing more details I decided this
wasn't actually worth a stable patch, and should just get folded into
later patches.

Thanks for the sanity-check!

Kees Cook

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