linux-kernel - Re: [PATCH] mm/kfence: add reboot notifier to disable KFENCE on shutdown

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Message-Id: <20251126101453.3ba9b3184aa6dd3c718287e6@linux-foundation.org>
Date: Wed, 26 Nov 2025 10:14:53 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Breno Leitao <leitao@...ian.org>
Cc: Alexander Potapenko <glider@...gle.com>, Marco Elver <elver@...gle.com>,
 Dmitry Vyukov <dvyukov@...gle.com>, kasan-dev@...glegroups.com,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org, kernel-team@...a.com
Subject: Re: [PATCH] mm/kfence: add reboot notifier to disable KFENCE on
 shutdown

On Wed, 26 Nov 2025 09:46:18 -0800 Breno Leitao <leitao@...ian.org> wrote:

> During system shutdown, KFENCE can cause IPI synchronization issues if
> it remains active through the reboot process. To prevent this, register
> a reboot notifier that disables KFENCE and cancels any pending timer
> work early in the shutdown sequence.
> 
> This is only necessary when CONFIG_KFENCE_STATIC_KEYS is enabled, as
> this configuration sends IPIs that can interfere with shutdown. Without
> static keys, no IPIs are generated and KFENCE can safely remain active.
> 
> The notifier uses maximum priority (INT_MAX) to ensure KFENCE shuts
> down before other subsystems that might still depend on stable memory
> allocation behavior.
> 
> This fixes a late kexec CSD lockup[1] when kfence is trying to IPI a CPU
> that is busy in a IRQ-disabled context printing characters to the
> console.
> 
> Link: https://lore.kernel.org/all/sqwajvt7utnt463tzxgwu2yctyn5m6bjwrslsnupfexeml6hkd@v6sqmpbu3vvu/ [1]

6.13 kernels and earlier, so I assume we'll want a cc:stable on this. 
And I assume there's really no identifiable Fixes: target.