linux-kernel - Re: [PATCH v6 3/4] atomic: Add alignment check to instrumented atomic operations

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Message-ID: <20260105160634.GA2393663@noisy.programming.kicks-ass.net>
Date: Mon, 5 Jan 2026 17:06:34 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Finn Thain <fthain@...ux-m68k.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Will Deacon <will@...nel.org>, Arnd Bergmann <arnd@...db.de>,
	Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
	Mark Rutland <mark.rutland@....com>, linux-arch@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-m68k@...ts.linux-m68k.org,
	Sasha Levin <sashal@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	Ard Biesheuvel <ardb@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
	linux-efi@...r.kernel.org
Subject: Re: [PATCH v6 3/4] atomic: Add alignment check to instrumented
 atomic operations

On Wed, Dec 31, 2025 at 07:25:42PM +1100, Finn Thain wrote:
> From: Peter Zijlstra <peterz@...radead.org>
> 
> Add a Kconfig option for debug builds which logs a warning when an
> instrumented atomic operation takes place that's misaligned.
> Some platforms don't trap for this.
> 
> [fthain: added __DISABLE_BUG_TABLE macro.]
> 
> Cc: Sasha Levin <sashal@...nel.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: x86@...nel.org
> Cc: Ard Biesheuvel <ardb@...nel.org>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Link: https://lore.kernel.org/lkml/20250901093600.GF4067720@noisy.programming.kicks-ass.net/
> Link: https://lore.kernel.org/linux-next/df9fbd22-a648-ada4-fee0-68fe4325ff82@linux-m68k.org/
> Signed-off-by: Finn Thain <fthain@...ux-m68k.org>
> ---
> Checkpatch.pl says...
> ERROR: Missing Signed-off-by: line by nominal patch author 'Peter Ziljstra <peterz@...radead.org>'
> ---
> Changed since v5:
>  - Add new __DISABLE_BUG_TABLE macro to prevent a build failure on those
> architectures which use atomics in pre-boot code like the EFI stub loader:
> 
> x86_64-linux-gnu-ld: error: unplaced orphan section `__bug_table' from `arch/x86/boot/compressed/sev-handle-vc.o'

Urgh, so why not simply use __DISABLE_EXPORTS, that's typically (ab)used
for these things?

Also, unless __DISABLE_BUG_TABLE goes live inside asm/bug.h and kills
all __bug_table emissions, its a misnomer.

Furthermore, that SEV thing is broken and needs to be fixed anyway, this
isn't helping it much. noinstr code should not be using instrumented
things to begin with.