linux-kernel - [PATCH v10 20/28] x86/resctrl: Add energy/perf choices to rdt boot option

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Message-ID: <20250912221053.11349-21-tony.luck@intel.com>
Date: Fri, 12 Sep 2025 15:10:41 -0700
From: Tony Luck <tony.luck@...el.com>
To: Fenghua Yu <fenghuay@...dia.com>,
	Reinette Chatre <reinette.chatre@...el.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,
	Tony Luck <tony.luck@...el.com>
Subject: [PATCH v10 20/28] x86/resctrl: Add energy/perf choices to rdt boot option

Legacy resctrl features are enumerated by X86_FEATURE_* flags. These
may be overridden by quirks to disable features in the case of errata.
Users can use kernel command line options to either disable a feature,
or to force enable a feature that was disabled by a quirk.

Provide similar functionality for hardware features that do not have an
X86_FEATURE_* flag.  Unlike other features that are tied to X86_FEATURE_*
flags, these must be queried by name. Add rdt_is_feature_enabled()
to check whether quirks or kernel command line have disabled a feature.

Users may force a feature to be disabled. E.g. "rdt=!perf" will ensure
that none of the perf telemetry events are enabled.

Resctrl architecture code may disable a feature that does not provide
full functionality. Users may override that decision.  E.g. "rdt=energy"
will enable any available energy telemetry events even if they do not
provide full functionality.

Signed-off-by: Tony Luck <tony.luck@...el.com>
---
 .../admin-guide/kernel-parameters.txt         |  2 +-
 arch/x86/kernel/cpu/resctrl/internal.h        |  2 ++
 arch/x86/kernel/cpu/resctrl/core.c            | 29 +++++++++++++++++++
 3 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 5bab2eff81eb..70b04e8198b7 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -6154,7 +6154,7 @@
 	rdt=		[HW,X86,RDT]
 			Turn on/off individual RDT features. List is:
 			cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
-			mba, smba, bmec, abmc.
+			mba, smba, bmec, abmc, energy, perf.
 			E.g. to turn on cmt and turn off mba use:
 				rdt=cmt,!mba
 
diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
index 592c7cf8e354..db71ce336af3 100644
--- a/arch/x86/kernel/cpu/resctrl/internal.h
+++ b/arch/x86/kernel/cpu/resctrl/internal.h
@@ -225,6 +225,8 @@ void __init intel_rdt_mbm_apply_quirk(void);
 void rdt_domain_reconfigure_cdp(struct rdt_resource *r);
 void resctrl_arch_mbm_cntr_assign_set_one(struct rdt_resource *r);
 
+bool rdt_is_feature_enabled(char *name);
+
 #ifdef CONFIG_X86_CPU_RESCTRL_INTEL_AET
 bool intel_aet_get_events(void);
 void __exit intel_aet_exit(void);
diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
index f493f9a2fdf5..2f789d8bd970 100644
--- a/arch/x86/kernel/cpu/resctrl/core.c
+++ b/arch/x86/kernel/cpu/resctrl/core.c
@@ -766,6 +766,8 @@ enum {
 	RDT_FLAG_SMBA,
 	RDT_FLAG_BMEC,
 	RDT_FLAG_ABMC,
+	RDT_FLAG_ENERGY,
+	RDT_FLAG_PERF,
 };
 
 #define RDT_OPT(idx, n, f)	\
@@ -792,6 +794,8 @@ static struct rdt_options rdt_options[]  __ro_after_init = {
 	RDT_OPT(RDT_FLAG_SMBA,	    "smba",	X86_FEATURE_SMBA),
 	RDT_OPT(RDT_FLAG_BMEC,	    "bmec",	X86_FEATURE_BMEC),
 	RDT_OPT(RDT_FLAG_ABMC,	    "abmc",	X86_FEATURE_ABMC),
+	RDT_OPT(RDT_FLAG_ENERGY,    "energy",	0),
+	RDT_OPT(RDT_FLAG_PERF,	    "perf",	0),
 };
 #define NUM_RDT_OPTIONS ARRAY_SIZE(rdt_options)
 
@@ -841,6 +845,31 @@ bool rdt_cpu_has(int flag)
 	return ret;
 }
 
+/*
+ * Hardware features that do not have X86_FEATURE_* bits. There is no
+ * "hardware does not support this at all" case. Assume that the caller
+ * has already determined that hardware support is present and just needs
+ * to check if the feature has been disabled by a quirk that has not been
+ * overridden by a command line option.
+ */
+bool rdt_is_feature_enabled(char *name)
+{
+	struct rdt_options *o;
+	bool ret = true;
+
+	for (o = rdt_options; o < &rdt_options[NUM_RDT_OPTIONS]; o++) {
+		if (!strcmp(name, o->name)) {
+			if (o->force_off)
+				ret = false;
+			if (o->force_on)
+				ret = true;
+			break;
+		}
+	}
+
+	return ret;
+}
+
 bool resctrl_arch_is_evt_configurable(enum resctrl_event_id evt)
 {
 	if (!rdt_cpu_has(X86_FEATURE_BMEC))
-- 
2.51.0