[PATCH v13 15/25] x86,fs/resctrl: Handle systems where AET is the only resource

[Tony Luck]

Application Energy Telemetry (AET) is not enumerated by CPUID its
presence/absence is discovered at file system mount time by querying the
pmt_telemetry driver. This results in two issues:

1) On a platform with no L3 monitoring features rdt_get_l3_mon_config()
   will report that the system does not support any monitoring at all.

   Handle this by optimistically assuming that AET may be supported.

2) If this optimism is unfounded, rdt_get_tree() may find that neither
   allocation, nor monitoring is supported. In this case it allows the
   mount to succeed, but does not set "resctrl_mounted".

   Move the feature test earlier and fail the mount with a diagnostic
   message to the console.

Signed-off-by: Tony Luck <tony.luck@xxxxxxxxx>
---
v13:
	Add a pr_info() if no L3 features are enabled on a
	"X86_FEATURE_CQM_LLC" system.

	Add a comment for the "return true" from get_rdt_mon_resources()

	Rewrite commit message with context for the change.
---
 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);
-- 
2.55.0