linux-kernel - Re: [PATCH] fs/proc: Expose mm

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Message-ID: <060edde3-7cc4-4a36-b9aa-824e607d954c@kernel.org>
Date: Thu, 18 Dec 2025 09:30:53 +0100
From: "David Hildenbrand (Red Hat)" <david@...nel.org>
To: Aaron Tomlin <atomlin@...mlin.com>, oleg@...hat.com,
 akpm@...ux-foundation.org, gregkh@...uxfoundation.org, brauner@...nel.org,
 mingo@...nel.org
Cc: sean@...e.io, linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] fs/proc: Expose mm_cpumask in /proc/[pid]/status

On 12/17/25 03:46, Aaron Tomlin wrote:
> This patch introduces two new fields to /proc/[pid]/status to display the
> set of CPUs, representing the CPU affinity of the process's active
> memory context, in both mask and list format: "Cpus_active_mm" and
> "Cpus_active_mm_list". The mm_cpumask is primarily used for TLB and
> cache synchronisation.
> 
> Exposing this information allows userspace to easily identify
> memory-task affinity, insight to NUMA alignment, CPU isolation and
> real-time workload placement.
> 
> Frequent mm_cpumask changes may indicate instability in placement
> policies or excessive task migration overhead.

I agree with Oleg's comments.

Given that everybody has read access to /proc/$PID/status IIUC, I wonder 
if that information could somehow help an attacker to better attack a 
target program (knowing which CPUs have dirty TLB etc). As you saise, 
it's primarily for TLB and cache sync ...

Just a thought, have nothing concrete in mind.

-- 
Cheers

David