linux-kernel - Re: [PATCH v6 05/30] x86,fs/resctrl: Improve domain type checking

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Message-ID: <fd40240d-353e-4c0c-9613-572df66e0055@intel.com>
Date: Tue, 8 Jul 2025 14:01:14 -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>, Anil Keshavamurthy <anil.s.keshavamurthy@...el.com>,
	Chen Yu <yu.c.chen@...el.com>
CC: <x86@...nel.org>, <linux-kernel@...r.kernel.org>,
	<patches@...ts.linux.dev>
Subject: Re: [PATCH v6 05/30] x86,fs/resctrl: Improve domain type checking

Hi Tony,

On 6/26/25 9:49 AM, Tony Luck wrote:
> The rdt_domain_hdr structure is used in both control and monitor
> domain structures to provide common methods for operations such as
> adding a CPU to a domain, removing a CPU from a domain, accessing
> the mask of all CPUs in a domain.
> 
> The "type" field provides a simple check whether a domain is a
> control or monitor domain so that programming errors operating
> on domains will be quickly caught.
> 
> To prepare for additional domain types that depend on the rdt_resource
> to which they are connected add the resource id into the header
> and check that in addition to the type.
> 
> At this point all monitoring events are tied to the RDT_RESOURCE_L3
> resource. So hard code the check in rdtgroup_mondata_show() to
> that resource id.

Comment about this hardcoding below ...

> 
> Signed-off-by: Tony Luck <tony.luck@...el.com>
> ---
>  include/linux/resctrl.h            |  9 +++++++++
>  arch/x86/kernel/cpu/resctrl/core.c | 10 ++++++----
>  fs/resctrl/ctrlmondata.c           |  2 +-
>  3 files changed, 16 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
> index 478d7a935ca3..dc7ccd60e8c2 100644
> --- a/include/linux/resctrl.h
> +++ b/include/linux/resctrl.h
> @@ -131,15 +131,24 @@ enum resctrl_domain_type {
>   * @list:		all instances of this resource
>   * @id:			unique id for this instance
>   * @type:		type of this instance
> + * @rid:		index of resource for this domain

Similar comment as in patch #1 about use of "index" in resctrl fs.

>   * @cpu_mask:		which CPUs share this resource
>   */
>  struct rdt_domain_hdr {
>  	struct list_head		list;
>  	int				id;
>  	enum resctrl_domain_type	type;
> +	enum resctrl_res_level		rid;
>  	struct cpumask			cpu_mask;
>  };
>  

...

> diff --git a/fs/resctrl/ctrlmondata.c b/fs/resctrl/ctrlmondata.c
> index ad7ffc6acf13..cdb4bc8baa99 100644
> --- a/fs/resctrl/ctrlmondata.c
> +++ b/fs/resctrl/ctrlmondata.c
> @@ -643,7 +643,7 @@ int rdtgroup_mondata_show(struct seq_file *m, void *arg)
>  		 * the resource to find the domain with "domid".
>  		 */
>  		hdr = resctrl_find_domain(&r->mon_domains, domid, NULL);
> -		if (!hdr || WARN_ON_ONCE(hdr->type != RESCTRL_MON_DOMAIN)) {
> +		if (!hdr || !domain_header_is_valid(hdr, RESCTRL_MON_DOMAIN, RDT_RESOURCE_L3)) {
>  			ret = -ENOENT;
>  			goto out;
>  		}

I do not see why this hardcoding is required since the resource ID is available via the
struct mon_data associated with the file. Looks like this is undone in patch #9 anyway
so the explicit handling by this patch is unclear.

Reinette