linux-kernel - Re: [PATCH] arm64/cpufeature: annotate arm64_use_ng_mappings with ro_after

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Message-ID: <aBULdGn+klwp8CEu@e129823.arm.com>
Date: Fri, 2 May 2025 19:14:12 +0100
From: Yeoreum Yun <yeoreum.yun@....com>
To: Catalin Marinas <catalin.marinas@....com>
Cc: Ard Biesheuvel <ardb@...nel.org>, will@...nel.org, nathan@...nel.org,
	nick.desaulniers+lkml@...il.com, morbo@...gle.com,
	justinstitt@...gle.com, broonie@...nel.org, maz@...nel.org,
	oliver.upton@...ux.dev, frederic@...nel.org, joey.gouly@....com,
	james.morse@....com, hardevsinh.palaniya@...iconsignals.io,
	shameerali.kolothum.thodi@...wei.com, ryan.roberts@....com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	llvm@...ts.linux.dev, stable@...r.kernel.org
Subject: Re: [PATCH] arm64/cpufeature: annotate arm64_use_ng_mappings with
 ro_after_init to prevent wrong idmap generation

> On Fri, May 02, 2025 at 06:41:33PM +0200, Ard Biesheuvel wrote:
> > Making arm64_use_ng_mappings __ro_after_init seems like a useful
> > change by itself, so I am not objecting to that. But we don't solve it
> > more fundamentally, please at least add a big fat comment why it is
> > important that the variable remains there.
>
> Maybe something like the section reference checker we use for __init -
> verify that the early C code does not refer anything in the BSS section.

Maybe but it would be better to be checked at compile time (I don't
know it's possible) otherwise, early C code writer should check
mandatroy by calling is_kernel_bss_data() (not exist) for data it refers.

> --
> Catalin

--
Sincerely,
Yeoreum Yun