linux-kernel - Re: [PATCH v11 06/31] x86,fs/resctrl: Use struct rdt_domain

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Message-ID: <f5a80f3a-1aaa-4831-a9f1-7f3eca748dfe@intel.com>
Date: Fri, 3 Oct 2025 08:34:01 -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 v11 06/31] x86,fs/resctrl: Use struct rdt_domain_hdr when
 reading counters

Hi Tony,

On 9/25/25 1:03 PM, Tony Luck wrote:
> Use a generic struct rdt_domain_hdr representing a generic domain
> header in struct rmid_read in order to support other telemetry events'
> domains besides an L3 one. Adjust the code interacting with it to the
> new struct layout.

I'd propose a small amend to be more specific and not assume reader knows
what rmid_read is used for:

	struct rmid_read contains data passed around to read event counts. Use the
	generic domain header struct rdt_domain_hdr in struct rmid_read in order to
	support other telemetry events' domains besides an L3 one. Adjust the code
	interacting with it to the new struct layout.


> diff --git a/fs/resctrl/ctrlmondata.c b/fs/resctrl/ctrlmondata.c
> index 3ceef35208be..7b9fc5d3bdc8 100644
> --- a/fs/resctrl/ctrlmondata.c
> +++ b/fs/resctrl/ctrlmondata.c
> @@ -550,13 +550,8 @@ void mon_event_read(struct rmid_read *rr, struct rdt_resource *r,
>  		    struct rdt_domain_hdr *hdr, struct rdtgroup *rdtgrp,
>  		    cpumask_t *cpumask, int evtid, int first)
>  {
> -	struct rdt_mon_domain *d;
>  	int cpu;
>  
> -	if (!domain_header_is_valid(hdr, RESCTRL_MON_DOMAIN, RDT_RESOURCE_L3))
> -		return;
> -	d = container_of(hdr, struct rdt_mon_domain, hdr);
> -

Problematic snippet removed here ...

>  	/* When picking a CPU from cpu_mask, ensure it can't race with cpuhp */
>  	lockdep_assert_cpus_held();
>  
> @@ -566,7 +561,7 @@ void mon_event_read(struct rmid_read *rr, struct rdt_resource *r,
>  	rr->rgrp = rdtgrp;
>  	rr->evtid = evtid;
>  	rr->r = r;
> -	rr->d = d;
> +	rr->hdr = hdr;
>  	rr->first = first;
>  	if (resctrl_arch_mbm_cntr_assign_enabled(r) &&
>  	    resctrl_is_mbm_event(evtid)) {
> diff --git a/fs/resctrl/monitor.c b/fs/resctrl/monitor.c
> index 4076336fbba6..32116361a5f6 100644
> --- a/fs/resctrl/monitor.c
> +++ b/fs/resctrl/monitor.c
> @@ -159,7 +159,7 @@ void __check_limbo(struct rdt_mon_domain *d, bool force_free)
>  			break;
>  
>  		entry = __rmid_entry(idx);
> -		if (resctrl_arch_rmid_read(r, d, entry->closid, entry->rmid,
> +		if (resctrl_arch_rmid_read(r, &d->hdr, entry->closid, entry->rmid,
>  					   QOS_L3_OCCUP_EVENT_ID, &val,
>  					   arch_mon_ctx)) {
>  			rmid_dirty = true;
> @@ -424,8 +424,12 @@ static int __mon_event_count(struct rdtgroup *rdtgrp, struct rmid_read *rr)
>  	int err, ret;
>  	u64 tval = 0;
>  
> +	if (!domain_header_is_valid(rr->hdr, RESCTRL_MON_DOMAIN, RDT_RESOURCE_L3))
> +		return -EINVAL;
> +	d = container_of(rr->hdr, struct rdt_mon_domain, hdr);
> +

... but now the problem is moved to __mon_event_count() where rr->hdr can be NULL and the
domain_header_is_valid() check is referencing NULL pointer when SNC is enabled?
Am I missing something here? Does this work on SNC?

Reinette