[PATCH v8 09/16] x86/resctrl: Drop global 'rdt_mon_capable' flag

[Tony Luck]

File system code calls resctrl_arch_mon_capable() to determine if the
system supports any monitoring features.

x86 architecture code sets a global flag to support implementation of
resctrl_arch_mon_capable() but the upcoming change to enumerate AET
(Application Energy Telemetry) features on each mount introduces a new
corner case.

Specifically when AET is the only monitoring feature, loading and
unloading the pmt_telemetry module between resctrl mounts may result
in monitoring support enabled on some mounts, but not on others.

Replace the global flag with a scan of resources to check if any are
marked mon_capable.

Signed-off-by: Tony Luck <tony.luck@xxxxxxxxx>

---
v8:
	Change from a count of monitor features to a scan of the
	rdt_resources checking for any that are mon_capable.

 arch/x86/include/asm/resctrl.h        |  6 +-----
 arch/x86/kernel/cpu/resctrl/core.c    | 18 +++++++++++++++---
 arch/x86/kernel/cpu/resctrl/monitor.c |  6 ------
 3 files changed, 16 insertions(+), 14 deletions(-)

diff --git a/arch/x86/include/asm/resctrl.h b/arch/x86/include/asm/resctrl.h
index 575f8408a9e7..a9f481b7a8ed 100644
--- a/arch/x86/include/asm/resctrl.h
+++ b/arch/x86/include/asm/resctrl.h
@@ -43,7 +43,6 @@ struct resctrl_pqr_state {
 DECLARE_PER_CPU(struct resctrl_pqr_state, pqr_state);
 
 extern bool rdt_alloc_capable;
-extern bool rdt_mon_capable;
 
 DECLARE_STATIC_KEY_FALSE(rdt_enable_key);
 DECLARE_STATIC_KEY_FALSE(rdt_alloc_enable_key);
@@ -66,10 +65,7 @@ static inline void resctrl_arch_disable_alloc(void)
 	static_branch_dec_cpuslocked(&rdt_enable_key);
 }
 
-static inline bool resctrl_arch_mon_capable(void)
-{
-	return rdt_mon_capable;
-}
+bool resctrl_arch_mon_capable(void);
 
 static inline void resctrl_arch_enable_mon(void)
 {
diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
index 7667cf7c4e94..fb6d52ea3406 100644
--- a/arch/x86/kernel/cpu/resctrl/core.c
+++ b/arch/x86/kernel/cpu/resctrl/core.c
@@ -50,6 +50,20 @@ DEFINE_PER_CPU(struct resctrl_pqr_state, pqr_state);
  */
 bool rdt_alloc_capable;
 
+/*
+ * Need to re-evaluate on each mount whether any mon_capable resources
+ * are enabled.
+ */
+bool resctrl_arch_mon_capable(void)
+{
+	struct rdt_resource *r;
+
+	for_each_mon_capable_rdt_resource(r)
+		return true;
+
+	return false;
+}
+
 static void mba_wrmsr_intel(struct msr_param *m);
 static void cat_wrmsr(struct msr_param *m);
 static void mba_wrmsr_amd(struct msr_param *m);
@@ -779,7 +793,6 @@ void resctrl_arch_pre_mount(void)
 	cpus_read_lock();
 	mutex_lock(&domain_list_lock);
 	r->mon_capable = true;
-	rdt_mon_capable = true;
 	for_each_online_cpu(cpu)
 		domain_add_cpu_mon(cpu, r);
 	mutex_unlock(&domain_list_lock);
@@ -1013,9 +1026,8 @@ static __init void check_quirks(void)
 static __init bool get_rdt_resources(void)
 {
 	rdt_alloc_capable = get_rdt_alloc_resources();
-	rdt_mon_capable = get_rdt_mon_resources();
 
-	return (rdt_mon_capable || rdt_alloc_capable);
+	return get_rdt_mon_resources() || rdt_alloc_capable;
 }
 
 static __init void rdt_init_res_defs_intel(void)
diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index 59215fef3924..682585fffe46 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -25,12 +25,6 @@
 
 #include "internal.h"
 
-/*
- * Global boolean for rdt_monitor which is true if any
- * resource monitoring is enabled.
- */
-bool rdt_mon_capable;
-
 #define CF(cf)	((unsigned long)(1048576 * (cf) + 0.5))
 
 static int snc_nodes_per_l3_cache = 1;
-- 
2.54.0