linux-kernel - Re: [PATCH v17 25/33] fs/resctrl: Provide interface to update the event configurations

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Message-ID: <c5f97d82-bb87-47e8-bbf0-e9dfca332313@intel.com>
Date: Tue, 2 Sep 2025 19:41:25 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Babu Moger <babu.moger@....com>, <corbet@....net>, <tony.luck@...el.com>,
	<tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
	<dave.hansen@...ux.intel.com>
CC: <Dave.Martin@....com>, <james.morse@....com>, <x86@...nel.org>,
	<hpa@...or.com>, <akpm@...ux-foundation.org>, <rostedt@...dmis.org>,
	<paulmck@...nel.org>, <pawan.kumar.gupta@...ux.intel.com>, <kees@...nel.org>,
	<arnd@...db.de>, <fvdl@...gle.com>, <seanjc@...gle.com>,
	<thomas.lendacky@....com>, <yosry.ahmed@...ux.dev>, <xin@...or.com>,
	<sohil.mehta@...el.com>, <kai.huang@...el.com>, <xiaoyao.li@...el.com>,
	<peterz@...radead.org>, <mario.limonciello@....com>, <xin3.li@...el.com>,
	<perry.yuan@....com>, <chang.seok.bae@...el.com>,
	<linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<peternewman@...gle.com>, <eranian@...gle.com>, <gautham.shenoy@....com>
Subject: Re: [PATCH v17 25/33] fs/resctrl: Provide interface to update the
 event configurations

Hi Babu,

On 8/14/25 7:25 PM, Babu Moger wrote:

> diff --git a/fs/resctrl/monitor.c b/fs/resctrl/monitor.c
> index 25fec9bf2d61..9201fedd2796 100644
> --- a/fs/resctrl/monitor.c
> +++ b/fs/resctrl/monitor.c
> @@ -1029,6 +1029,125 @@ int event_filter_show(struct kernfs_open_file *of, struct seq_file *seq, void *v
>  	return ret;
>  }
>  
> +static int resctrl_parse_mem_transactions(char *tok, u32 *val)
> +{
> +	u32 temp_val = 0;
> +	char *evt_str;
> +	bool found;
> +	int i;
> +
> +next_config:
> +	if (!tok || tok[0] == '\0') {
> +		*val = temp_val;
> +		return 0;
> +	}

Looks like resctrl_parse_mem_transactions() can return "success" with a parsed
return value of "0" (*val = 0) ... (follow-up comment in event_filter_write()).

> +
> +	/* Start processing the strings for each memory transaction type */
> +	evt_str = strim(strsep(&tok, ","));
> +	found = false;
> +	for (i = 0; i < NUM_MBM_TRANSACTIONS; i++) {
> +		if (!strcmp(mbm_transactions[i].name, evt_str)) {
> +			temp_val |= mbm_transactions[i].val;
> +			found = true;
> +			break;
> +		}
> +	}
> +
> +	if (!found) {
> +		rdt_last_cmd_printf("Invalid memory transaction type %s\n", evt_str);
> +		return -EINVAL;
> +	}
> +
> +	goto next_config;
> +}
> +
> +/*
> + * rdtgroup_update_cntr_event - Update the counter assignments for the event
> + *				in a group.
> + * @r:		Resource to which update needs to be done.
> + * @rdtgrp:	Resctrl group.
> + * @evtid:	MBM monitor event.
> + */
> +static void rdtgroup_update_cntr_event(struct rdt_resource *r, struct rdtgroup *rdtgrp,
> +				       enum resctrl_event_id evtid)
> +{
> +	struct rdt_mon_domain *d;
> +	struct mbm_state *m;
> +	int cntr_id;
> +
> +	list_for_each_entry(d, &r->mon_domains, hdr.list) {
> +		cntr_id = mbm_cntr_get(r, d, rdtgrp, evtid);
> +		if (cntr_id >= 0) {
> +			resctrl_arch_config_cntr(r, d, evtid, rdtgrp->mon.rmid,
> +						 rdtgrp->closid, cntr_id, true);
> +			m = get_mbm_state(d, rdtgrp->closid, rdtgrp->mon.rmid, evtid);
> +			if (m)
> +				memset(m, 0, sizeof(*m));

This looks like open code of rdtgroup_assign_cntr()?

> +		}
> +	}
> +}
> +

...

> +
> +ssize_t event_filter_write(struct kernfs_open_file *of, char *buf, size_t nbytes,
> +			   loff_t off)
> +{
> +	struct mon_evt *mevt = rdt_kn_parent_priv(of->kn);
> +	struct rdt_resource *r;
> +	u32 evt_cfg = 0;
> +	int ret = 0;
> +
> +	/* Valid input requires a trailing newline */
> +	if (nbytes == 0 || buf[nbytes - 1] != '\n')
> +		return -EINVAL;
> +
> +	buf[nbytes - 1] = '\0';
> +
> +	cpus_read_lock();
> +	mutex_lock(&rdtgroup_mutex);
> +
> +	rdt_last_cmd_clear();
> +
> +	r = resctrl_arch_get_resource(mevt->rid);
> +	if (!resctrl_arch_mbm_cntr_assign_enabled(r)) {
> +		rdt_last_cmd_puts("mbm_event counter assignment mode is not enabled\n");
> +		ret = -EINVAL;
> +		goto out_unlock;
> +	}
> +
> +	ret = resctrl_parse_mem_transactions(buf, &evt_cfg);
> +	if (!ret && mevt->evt_cfg != evt_cfg) {

... is evt_cfg of 0 (a) a valid value (that will not cause hardware to fault) and
(b) a reasonable value to allow? 

Reinette