linux-kernel - [PATCH v7 19/24] x86/resctrl: Report "Unassigned" for MBM events in mbm_cntr

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Message-ID: <1c5b054d8fbc3f7ad22c686d0d5e21e6573187bd.1725488488.git.babu.moger@amd.com>
Date: Wed, 4 Sep 2024 17:21:34 -0500
From: Babu Moger <babu.moger@....com>
To: <corbet@....net>, <fenghua.yu@...el.com>, <reinette.chatre@...el.com>,
	<tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
	<dave.hansen@...ux.intel.com>
CC: <x86@...nel.org>, <hpa@...or.com>, <paulmck@...nel.org>,
	<rdunlap@...radead.org>, <tj@...nel.org>, <peterz@...radead.org>,
	<yanjiewtw@...il.com>, <babu.moger@....com>, <kim.phillips@....com>,
	<lukas.bulwahn@...il.com>, <seanjc@...gle.com>, <jmattson@...gle.com>,
	<leitao@...ian.org>, <jpoimboe@...nel.org>, <rick.p.edgecombe@...el.com>,
	<kirill.shutemov@...ux.intel.com>, <jithu.joseph@...el.com>,
	<kai.huang@...el.com>, <kan.liang@...ux.intel.com>,
	<daniel.sneddon@...ux.intel.com>, <pbonzini@...hat.com>,
	<sandipan.das@....com>, <ilpo.jarvinen@...ux.intel.com>,
	<peternewman@...gle.com>, <maciej.wieczor-retman@...el.com>,
	<linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<eranian@...gle.com>, <james.morse@....com>
Subject: [PATCH v7 19/24] x86/resctrl: Report "Unassigned" for MBM events in mbm_cntr_assign mode

In mbm_cntr_assign mode, the hardware counter should be assigned to read
the MBM events.

Report "Unassigned" in case the user attempts to read the events without
assigning the counter.

Signed-off-by: Babu Moger <babu.moger@....com>
---
v7: Moved the documentation under "mon_data".
    Updated the text little bit.

v6: Added more explaination in the resctrl.rst
    Added checks to detect "Unassigned" before reading RMID.

v5: New patch.
---
 Documentation/arch/x86/resctrl.rst        | 10 ++++++++++
 arch/x86/kernel/cpu/resctrl/ctrlmondata.c | 13 ++++++++++++-
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst
index 3e9302971faf..ff5397d19704 100644
--- a/Documentation/arch/x86/resctrl.rst
+++ b/Documentation/arch/x86/resctrl.rst
@@ -417,6 +417,16 @@ When monitoring is enabled all MON groups will also contain:
 	for the L3 cache they occupy). These are named "mon_sub_L3_YY"
 	where "YY" is the node number.
 
+	The mbm_cntr_assign mode allows users to assign a hardware counter
+	to an RMID-event pair, enabling bandwidth monitoring for as long
+	as the counter remains assigned. The hardware will continue tracking
+	the assigned RMID until the user manually unassigns it, ensuring
+	that counters are not reset during this period. With a limited number
+	of counters, the system may run out of assignable resources. In
+	mbm_cntr_assign mode, MBM event counters will return "Unassigned"
+	if the counter is not allocated to the event when read. Users must
+	manually assign a counter to read the events.
+
 "mon_hw_id":
 	Available only with debug option. The identifier used by hardware
 	for the monitor group. On x86 this is the RMID.
diff --git a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
index 50fa1fe9a073..fc19b1d131b2 100644
--- a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
+++ b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
@@ -562,7 +562,7 @@ int rdtgroup_mondata_show(struct seq_file *m, void *arg)
 	struct rdtgroup *rdtgrp;
 	struct rdt_resource *r;
 	union mon_data_bits md;
-	int ret = 0;
+	int ret = 0, index;
 
 	rdtgrp = rdtgroup_kn_lock_live(of->kn);
 	if (!rdtgrp) {
@@ -576,6 +576,15 @@ int rdtgroup_mondata_show(struct seq_file *m, void *arg)
 	evtid = md.u.evtid;
 	r = &rdt_resources_all[resid].r_resctrl;
 
+	if (resctrl_arch_mbm_cntr_assign_enabled(r) && evtid != QOS_L3_OCCUP_EVENT_ID) {
+		index = mon_event_config_index_get(evtid);
+		if (index != INVALID_CONFIG_INDEX &&
+		    rdtgrp->mon.cntr_id[index] == MON_CNTR_UNSET) {
+			rr.err = -ENOENT;
+			goto checkresult;
+		}
+	}
+
 	if (md.u.sum) {
 		/*
 		 * This file requires summing across all domains that share
@@ -613,6 +622,8 @@ int rdtgroup_mondata_show(struct seq_file *m, void *arg)
 		seq_puts(m, "Error\n");
 	else if (rr.err == -EINVAL)
 		seq_puts(m, "Unavailable\n");
+	else if (rr.err == -ENOENT)
+		seq_puts(m, "Unassigned\n");
 	else
 		seq_printf(m, "%llu\n", rr.val);
 
-- 
2.34.1