[RFC PATCH 1/4] x86/resctrl: Check if monitoring features are enabled

[Tony Luck]

Both Intel and AMD manuals say that software must first check
CPUID(0x7,0x0).EBX[12] to see if any monitoring features are enabled
before checking for specific features enabled in subleaves.

Add the check for X86_FEATURE_CQM.

Fixes: cbc82b172638 ("x86: Add support for Intel Cache QoS Monitoring (CQM) detection")
Signed-off-by: Tony Luck <tony.luck@xxxxxxxxx>
---
 arch/x86/kernel/cpu/resctrl/core.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
index 55214d6fdc49..2677b8a6c15b 100644
--- a/arch/x86/kernel/cpu/resctrl/core.c
+++ b/arch/x86/kernel/cpu/resctrl/core.c
@@ -968,6 +968,9 @@ static __init bool get_rdt_mon_resources(void)
 	struct rdt_resource *r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
 	bool ret = false;
 
+	if (!cpu_feature_enabled(X86_FEATURE_CQM))
+		return false;
+
 	if (rdt_cpu_has(X86_FEATURE_CQM_OCCUP_LLC)) {
 		resctrl_enable_mon_event(QOS_L3_OCCUP_EVENT_ID, false, 0, NULL);
 		ret = true;
-- 
2.55.0