[PATCH v14 14/24] x86,fs/resctrl: Handle systems where AET is the only monitoring feature

[Tony Luck]

Application Energy Telemetry (AET) is not enumerated via CPUID. Its presence
is discovered on the first mount of the resctrl file system by querying the
pmt_telemetry driver. resctrl is initialized at boot only if CPUID
enumeration finds allocation or monitoring features.

On a system that supports monitoring (X86_FEATURE_CQM) but no L3 monitoring
features, get_rdt_mon_resources() reports that no monitoring is supported.
If the system also does not support allocation, resctrl is not initialized
and AET can never be used.

Assume that AET may be supported whenever the system supports monitoring.

If AET is not supported either, the mount finds neither allocation nor
monitoring support. rdt_get_tree() then lets the mount succeed with nothing
to allocate or monitor, but does not mark resctrl as mounted. Fail the mount
with an error message instead, before any of the file system is set up.

Signed-off-by: Tony Luck <tony.luck@xxxxxxxxx>
---
v14:
	New commit message.
---
 arch/x86/kernel/cpu/resctrl/internal.h |  2 +-
 arch/x86/kernel/cpu/resctrl/core.c     | 22 +++++++++++++---------
 arch/x86/kernel/cpu/resctrl/monitor.c  |  4 +---
 fs/resctrl/rdtgroup.c                  |  8 ++++++--
 4 files changed, 21 insertions(+), 15 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
index 086282a82fca..c038b7d80ce3 100644
--- a/arch/x86/kernel/cpu/resctrl/internal.h
+++ b/arch/x86/kernel/cpu/resctrl/internal.h
@@ -226,7 +226,7 @@ union l3_qos_abmc_cfg {
 
 void rdt_ctrl_update(void *arg);
 
-int rdt_get_l3_mon_config(struct rdt_resource *r);
+void rdt_get_l3_mon_config(struct rdt_resource *r);
 
 bool rdt_cpu_has(int flag);
 
diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
index b32fa143283e..0262174df7ad 100644
--- a/arch/x86/kernel/cpu/resctrl/core.c
+++ b/arch/x86/kernel/cpu/resctrl/core.c
@@ -991,7 +991,7 @@ static __init bool get_rdt_alloc_resources(void)
 static __init bool get_rdt_mon_resources(void)
 {
 	struct rdt_resource *r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
-	bool ret = false;
+	bool l3_mon_found = false;
 
 	/* Any monitoring at all? */
 	if (!cpu_feature_enabled(X86_FEATURE_CQM))
@@ -1001,27 +1001,31 @@ static __init bool get_rdt_mon_resources(void)
 
 	/* Any of the L3 monitoring features? */
 	if (!cpu_feature_enabled(X86_FEATURE_CQM_LLC))
-		return false;
+		goto out;
 
 	if (rdt_cpu_has(X86_FEATURE_CQM_OCCUP_LLC)) {
 		resctrl_enable_mon_event(QOS_L3_OCCUP_EVENT_ID, false, 0, NULL);
-		ret = true;
+		l3_mon_found = true;
 	}
 	if (rdt_cpu_has(X86_FEATURE_CQM_MBM_TOTAL)) {
 		resctrl_enable_mon_event(QOS_L3_MBM_TOTAL_EVENT_ID, false, 0, NULL);
-		ret = true;
+		l3_mon_found = true;
 	}
 	if (rdt_cpu_has(X86_FEATURE_CQM_MBM_LOCAL)) {
 		resctrl_enable_mon_event(QOS_L3_MBM_LOCAL_EVENT_ID, false, 0, NULL);
-		ret = true;
+		l3_mon_found = true;
 	}
 	if (rdt_cpu_has(X86_FEATURE_ABMC))
-		ret = true;
+		l3_mon_found = true;
 
-	if (!ret)
-		return false;
+	if (l3_mon_found)
+		rdt_get_l3_mon_config(r);
+	else
+		pr_info("CPUID reports L3 monitoring support, but no L3 monitoring features found\n");
 
-	return !rdt_get_l3_mon_config(r);
+out:
+	/* Non-L3 features, e.g. AET, may be supported */
+	return true;
 }
 
 static __init void __check_quirks_intel(void)
diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index 82a555855c1b..bd45d72d1d05 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -431,7 +431,7 @@ static void __init intel_rdt_mbm_apply_quirk(u32 num_rmid)
 	mbm_cf = mbm_cf_table[cf_index].cf;
 }
 
-int __init rdt_get_l3_mon_config(struct rdt_resource *r)
+void __init rdt_get_l3_mon_config(struct rdt_resource *r)
 {
 	struct rdt_hw_resource *hw_res = resctrl_to_arch_res(r);
 	unsigned int mbm_offset;
@@ -519,8 +519,6 @@ int __init rdt_get_l3_mon_config(struct rdt_resource *r)
 		intel_rdt_mbm_apply_quirk(num_rmid);
 
 	r->mon_capable = true;
-
-	return 0;
 }
 
 static void resctrl_abmc_set_one_amd(void *arg)
diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
index 79d4ddc3d64d..ecdb5da50179 100644
--- a/fs/resctrl/rdtgroup.c
+++ b/fs/resctrl/rdtgroup.c
@@ -3193,6 +3193,11 @@ static int rdt_get_tree(struct fs_context *fc)
 		goto out;
 	}
 
+	if (!resctrl_alloc_capable() && !resctrl_mon_capable()) {
+		ret = invalfc(fc, "No allocation or monitoring features are available or enabled");
+		goto out;
+	}
+
 	ret = setup_rmid_lru_list();
 	if (ret)
 		goto out;
@@ -3251,8 +3256,7 @@ static int rdt_get_tree(struct fs_context *fc)
 	if (resctrl_mon_capable())
 		resctrl_arch_enable_mon();
 
-	if (resctrl_alloc_capable() || resctrl_mon_capable())
-		resctrl_mounted = true;
+	resctrl_mounted = true;
 
 	if (resctrl_is_mbm_enabled()) {
 		r = resctrl_arch_get_resource(RDT_RESOURCE_L3);
-- 
2.56.0