linux-kernel - Re: [PATCH v2] x86/kfence: Fix booting on 32bit non-PAE systems

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Message-Id: <20260126132450.fe903384a227a558fab50536@linux-foundation.org>
Date: Mon, 26 Jan 2026 13:24:50 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Andrew Cooper <andrew.cooper3@...rix.com>
Cc: LKML <linux-kernel@...r.kernel.org>, Ryusuke Konishi
 <konishi.ryusuke@...il.com>, Alexander Potapenko <glider@...gle.com>, Marco
 Elver <elver@...gle.com>, Dmitry Vyukov <dvyukov@...gle.com>, 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, "H. Peter Anvin" <hpa@...or.com>, Jann Horn
 <jannh@...gle.com>, kasan-dev@...glegroups.com
Subject: Re: [PATCH v2] x86/kfence: Fix booting on 32bit non-PAE systems

On Mon, 26 Jan 2026 21:10:46 +0000 Andrew Cooper <andrew.cooper3@...rix.com> wrote:

> The original patch inverted the PTE unconditionally to avoid
> L1TF-vulnerable PTEs, but Linux doesn't make this adjustment in 2-level
> paging.
> 
> Adjust the logic to use the flip_protnone_guard() helper, which is a nop on
> 2-level paging but inverts the address bits in all other paging modes.
> 
> This doesn't matter for the Xen aspect of the original change.  Linux no
> longer supports running 32bit PV under Xen, and Xen doesn't support running
> any 32bit PV guests without using PAE paging.

Great thanks.  I'll add

	Tested-by: Ryusuke Konishi <konishi.ryusuke@...il.com>

and, importantly,

	Cc: <stable@...r.kernel.org>

to help everything get threaded together correctly.

I'll queue this as a 6.19-rcX hotfix.