linux-kernel - Re: [PATCH v12 18/31] fs/resctrl: Split L3 dependent parts out of __mon_event

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <c6a929dc-0362-499b-bdf8-7f0cb43e8402@intel.com>
Date: Wed, 22 Oct 2025 21:37:22 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Tony Luck <tony.luck@...el.com>, Fenghua Yu <fenghuay@...dia.com>, "Maciej
 Wieczor-Retman" <maciej.wieczor-retman@...el.com>, Peter Newman
	<peternewman@...gle.com>, James Morse <james.morse@....com>, Babu Moger
	<babu.moger@....com>, Drew Fustini <dfustini@...libre.com>, Dave Martin
	<Dave.Martin@....com>, Chen Yu <yu.c.chen@...el.com>
CC: <x86@...nel.org>, <linux-kernel@...r.kernel.org>,
	<patches@...ts.linux.dev>
Subject: Re: [PATCH v12 18/31] fs/resctrl: Split L3 dependent parts out of
 __mon_event_count()

Hi Tony,

On 10/13/25 3:33 PM, Tony Luck wrote:
> Almost all of the code in __mon_event_count() is specific to the RDT_RESOURCE_L3
> resource.
> 
> Split it out into __l3_mon_event_count().

Missing a "why". We could perhaps write it similar to an earlier commit message:
	Carve out the L3 resource specific event reading code into a separate
	helper to support reading event data from a new monitoring resource.

> 
> Suggested-by: Reinette Chatre <reinette.chatre@...el.com>
> Signed-off-by: Tony Luck <tony.luck@...el.com>
> ---


> @@ -529,6 +499,44 @@ static int __mon_event_count(struct rdtgroup *rdtgrp, struct rmid_read *rr)
>  	return ret;
>  }
>  
> +/*
> + * Called from preemptible context via a direct call of mon_event_count() for
> + * events that can be read on any CPU.
> + * Called from preemptible but non-migratable process context (mon_event_count()
> + * via smp_call_on_cpu()) OR non-preemptible context (mon_event_count() via
> + * smp_call_function_any()) for events that need to be read on a specific CPU.
> + */
> +static bool cpu_on_correct_domain(struct rmid_read *rr)
> +{
> +	int cpu;
> +
> +	/* Any CPU is OK for this event */
> +	if (rr->evt->any_cpu)
> +		return true;
> +
> +	cpu = smp_processor_id();
> +
> +	/* Single domain. Must be on a CPU in that domain. */
> +	if (rr->hdr)
> +		return cpumask_test_cpu(cpu, &rr->hdr->cpu_mask);
> +
> +	/* Summing domains that share a cache, must be on a CPU for that cache. */
> +	return cpumask_test_cpu(cpu, &rr->ci->shared_cpu_map);
> +}
> +
> +static int __mon_event_count(struct rdtgroup *rdtgrp, struct rmid_read *rr)
> +{
> +	if (!cpu_on_correct_domain(rr))
> +		return -EINVAL;

It is a bit subtle how cpu_on_correct_domain() contains L3 specific code.
This may be ok if one rather thinks of it as a sanity check of struct rmid_read.

Reinette