linux-kernel - Re: [RFC/RFT PATCH 01/19] x86/idt: Move idt_table to __ro_after

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Message-ID: <CAMj1kXH6XCTCeEFDkn+8zygWR=Oq-h57VV3YyX+n+CjH98eNKg@mail.gmail.com>
Date: Thu, 22 Jan 2026 15:20:39 +0100
From: Ard Biesheuvel <ardb@...nel.org>
To: Borislav Petkov <bp@...en8.de>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org, 
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, "H. Peter Anvin" <hpa@...or.com>, 
	Josh Poimboeuf <jpoimboe@...nel.org>, Peter Zijlstra <peterz@...radead.org>, Kees Cook <kees@...nel.org>, 
	Uros Bizjak <ubizjak@...il.com>, Brian Gerst <brgerst@...il.com>, linux-hardening@...r.kernel.org
Subject: Re: [RFC/RFT PATCH 01/19] x86/idt: Move idt_table to __ro_after_init section

On Thu, 22 Jan 2026 at 15:16, Borislav Petkov <bp@...en8.de> wrote:
>
> On Thu, Jan 22, 2026 at 03:09:19PM +0100, Ard Biesheuvel wrote:
> > It does. It just doesn't prevent if from happening for other reasons.
>
> So this reads to me like "it does but it doesn't". Huh?!?
>
> C'mon Ard, let's be more precise pls.
>

Fair enough. What I meant to say is that if your BSS placed on a 2M
boundary or is sufficiently larger than that, some of it will be
mapped using PMDs, and this change will prevent those from being
broken up into page mappings. If your BSS is too small to be covered
by huge page mappings in the first place, this change obviously does
nothing (except fixing a bug on i386)