perf/x86/intel: Disable PMI for self-reloaded ACR events

[ Upstream commit 1271aeccc307066315b2d3b0d5af2510e27018b5 ]

On platforms with Auto Counter Reload (ACR) support, such as NVL, a
"NMI received for unknown reason 30" warning is observed when running
multiple events in a group with ACR enabled:

  $ perf record -e '{instructions/period=20000,acr_mask=0x2/u,\
    cycles/period=40000,acr_mask=0x3/u}' ./test

The warning occurs because the Performance Monitoring Interrupt (PMI)
is enabled for the self-reloaded event (the cycles event in this case).
According to the Intel SDM, the overflow bit
(IA32_PERF_GLOBAL_STATUS.PMCn_OVF) is never set for self-reloaded events.
Since the bit is not set, the perf NMI handler cannot identify the source
of the interrupt, leading to the "unknown reason" message.

Furthermore, enabling PMI for self-reloaded events is unnecessary and
can lead to extraneous records that pollute the user's requested data.

Disable the interrupt bit for all events configured with ACR self-reload.

Fixes: ec980e4 ("perf/x86/intel: Support auto counter reload")
Reported-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260430002558.712334-4-dapeng1.mi@linux.intel.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Dapeng Mi

arch/x86/events/intel/core.c

@@ -2866,11 +2866,11 @@ static void intel_pmu_enable_fixed(struct perf_event *event)
 	intel_set_masks(event, idx);
 
 	/*
-	 * Enable IRQ generation (0x8), if not PEBS,
-	 * and enable ring-3 counting (0x2) and ring-0 counting (0x1)
-	 * if requested:
+	 * Enable IRQ generation (0x8), if not PEBS or self-reloaded
+	 * ACR event, and enable ring-3 counting (0x2) and ring-0
+	 * counting (0x1) if requested:
 	 */
-	if (!event->attr.precise_ip)
+	if (!event->attr.precise_ip && !is_acr_self_reload_event(event))
 		bits |= INTEL_FIXED_0_ENABLE_PMI;
 	if (hwc->config & ARCH_PERFMON_EVENTSEL_USR)
 		bits |= INTEL_FIXED_0_USER;
@@ -2955,6 +2955,15 @@ static void intel_pmu_enable_event(struct perf_event *event)
 			enable_mask |= ARCH_PERFMON_EVENTSEL_BR_CNTR;
 		intel_set_masks(event, idx);
 		static_call_cond(intel_pmu_enable_acr_event)(event);
+		/*
+		 * For self-reloaded ACR event, don't enable PMI since
+		 * HW won't set overflow bit in GLOBAL_STATUS. Otherwise,
+		 * the PMI would be recognized as a suspicious NMI.
+		 */
+		if (is_acr_self_reload_event(event))
+			hwc->config &= ~ARCH_PERFMON_EVENTSEL_INT;
+		else if (!event->attr.precise_ip)
+			hwc->config |= ARCH_PERFMON_EVENTSEL_INT;
 		__x86_pmu_enable_event(hwc, enable_mask);
 		break;
 	case INTEL_PMC_IDX_FIXED ... INTEL_PMC_IDX_FIXED_BTS - 1:

arch/x86/events/perf_event.h

@@ -133,6 +133,16 @@ static inline bool is_acr_event_group(struct perf_event *event)
 	return check_leader_group(event->group_leader, PERF_X86_EVENT_ACR);
 }
 
+static inline bool is_acr_self_reload_event(struct perf_event *event)
+{
+	struct hw_perf_event *hwc = &event->hw;
+
+	if (hwc->idx < 0)
+		return false;
+
+	return test_bit(hwc->idx, (unsigned long *)&hwc->config1);
+}
+
 struct amd_nb {
 	int nb_id;  /* NorthBridge id */
 	int refcnt; /* reference count */