Re: [PATCH] fs/proc: Expose mm_cpumask in /proc/[pid]/status

["David Hildenbrand (Red Hat)" <david@kernel.org>]

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