linux-kernel - Re: [PATCH v4 07/21] x86/resctrl: Create mba_sc configuration in the rdt

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Date:   Tue, 17 May 2022 09:18:53 -0700
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     James Morse <james.morse@....com>, <x86@...nel.org>,
        <linux-kernel@...r.kernel.org>
CC:     Fenghua Yu <fenghua.yu@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        H Peter Anvin <hpa@...or.com>,
        Babu Moger <Babu.Moger@....com>,
        <shameerali.kolothum.thodi@...wei.com>,
        D Scott Phillips OS <scott@...amperecomputing.com>,
        <lcherian@...vell.com>, <bobo.shaobowang@...wei.com>,
        <tan.shaopeng@...itsu.com>, Jamie Iles <quic_jiles@...cinc.com>,
        Cristian Marussi <cristian.marussi@....com>,
        "Xin Hao" <xhao@...ux.alibaba.com>, <xingxin.hx@...nanolis.org>,
        <baolin.wang@...ux.alibaba.com>
Subject: Re: [PATCH v4 07/21] x86/resctrl: Create mba_sc configuration in the
 rdt_domain

Hi James,

On 4/12/2022 5:44 AM, James Morse wrote:

...

> @@ -3263,6 +3295,7 @@ void resctrl_offline_domain(struct rdt_resource *r, struct rdt_domain *d)
>  		cancel_delayed_work(&d->cqm_limbo);
>  	}
>  
> +	mba_sc_domain_destroy(r, d);
>  	domain_destroy_mon_state(d);
>  }

It is not clear to me how rdt_domain->mbps_val will be released via the above call.

After patch 3/21 and the hunk below resctrl_online_domain() would look like:

resctrl_online_domain() {
	
	int err;

	lockdep_assert_held(&rdtgroup_mutex);

	if (is_mbm_enabled() && r->rid == RDT_RESOURCE_MBA) {
		err = mba_sc_domain_allocate(r, d);
		if (err)
			return err;
	}
	
	if (!r->mon_capable)
		return 0;

	...
}
	
If I understand the above correctly, if MBM is enabled then all domains
of resource RDT_RESOURCE_MBA will have rdt_domain->mbps_val allocated via
resctrl_online_domain().

RDT_RESOURCE_MBA is not mon_capable, so at the time its domains go
offline, the freeing of rdt_domain->mbps_val will be skipped because	
after patch 5/21 resctrl_offline_domain() would look like below so
I do not see how the hunk added above will ever end up cleaning up
allocated memory:

resctrl_offline_domain() {

	lockdep_assert_held(&rdtgroup_mutex);

	if (!r->mon_capable) /* RDT_RESOURCE_MBA is not mon_capable */
		return 0;

	...

	
	mba_sc_domain_destroy(r, d); /* Not reached for rdt_domains of RDT_RESOURCE_MBA */
	domain_destroy_mon_state(d);
}

>  
> @@ -3302,12 +3335,20 @@ int resctrl_online_domain(struct rdt_resource *r, struct rdt_domain *d)
>  
>  	lockdep_assert_held(&rdtgroup_mutex);
>  
> +	if (is_mbm_enabled() && r->rid == RDT_RESOURCE_MBA) {

This introduces only half of the checks that are later replaced in
patch 10 "x86/resctrl: Abstract and use supports_mba_mbps()". Could the
full check be used here for that patch to be cleaner or perhaps patch 10
could be moved to be before this patch?

> +		err = mba_sc_domain_allocate(r, d);
> +		if (err)
> +			return err;
> +	}
> +
>  	if (!r->mon_capable)
>  		return 0;
>  
>  	err = domain_setup_mon_state(r, d);
> -	if (err)
> +	if (err) {
> +		mba_sc_domain_destroy(r, d);
>  		return err;
> +	}

Cleaning up after the error is reasonable but this allocation would only
ever happen if the resource is RDT_RESOURCE_MBA and it is not mon_capable.
Something would thus have gone really wrong if this cleanup is necessary.
Considering that only mon_capable resources are initialized at this point,
why not just exit right after calling mba_sc_domain_allocate()?


>  
>  	if (is_mbm_enabled()) {
>  		INIT_DELAYED_WORK(&d->mbm_over, mbm_handle_overflow);
> diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
> index 5d283bdd6162..46ab9fb5562e 100644
> --- a/include/linux/resctrl.h
> +++ b/include/linux/resctrl.h
> @@ -15,6 +15,9 @@ int proc_resctrl_show(struct seq_file *m,
>  
>  #endif
>  
> +/* max value for struct rdt_domain's mbps_val */
> +#define MBA_MAX_MBPS   U32_MAX
> +
>  /**
>   * enum resctrl_conf_type - The type of configuration.
>   * @CDP_NONE:	No prioritisation, both code and data are controlled or monitored.
> @@ -53,6 +56,9 @@ struct resctrl_staged_config {
>   * @cqm_work_cpu:	worker CPU for CQM h/w counters
>   * @plr:		pseudo-locked region (if any) associated with domain
>   * @staged_config:	parsed configuration to be applied
> + * @mbps_val:		When mba_sc is enabled, this holds the array of user
> + * 			specified control values for mba_sc in MBps, indexed
> + *			by closid
>   */
>  struct rdt_domain {
>  	struct list_head		list;
> @@ -67,6 +73,7 @@ struct rdt_domain {
>  	int				cqm_work_cpu;
>  	struct pseudo_lock_region	*plr;
>  	struct resctrl_staged_config	staged_config[CDP_NUM_TYPES];
> +	u32				*mbps_val;
>  };
>  
>  /**

Reinette