perf/x86/intel: Prevent drain_pebs() reentry

The PEBS buffer is shared by all events on a CPU, so drain_pebs() must
not be reentered. If so, one instance may observe stale buffer state and
potentially access out-of-bound memory.

Most invocations happen in NMI context, which naturally prevents reentry.
However, drain_pebs() is also reachable from process context via
intel_pmu_drain_pebs_buffer().

In those paths, the PMU is often already disabled, but not guaranteed.
For example, __intel_pmu_pebs_disable() only disables the target counter,
so other active counters can still raise a PMI and interrupt an in-flight
drain_pebs(). Here is an example,

__perf_addr_filters_adjust()
  perf_event_stop()
    __perf_event_stop()
      x86_pmu_stop() (event->pmu->stop)
        intel_pmu_disable_event()
          intel_pmu_pebs_disable()
            __intel_pmu_pebs_disable()
              intel_pmu_drain_large_pebs()
                intel_pmu_drain_pebs_buffer()

Introduce __intel_pmu_quiesce() and __intel_pmu_resume() helpers and
use them in intel_pmu_drain_large_pebs() to disable the full PMU
around the intel_pmu_drain_pebs_buffer() call, preventing reentry.

Also add a warning in intel_pmu_drain_pebs_buffer() when the full PMU is
not disabled.

Fixes: b752ea0c28 ("perf/x86/intel/ds: Flush PEBS DS when changing PEBS_DATA_CFG")
Signed-off-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260813064346.335458-1-dapeng1.mi@linux.intel.com

arch/x86/events/intel/core.c

@@ -3125,6 +3125,27 @@ static void intel_pmu_del_event(struct perf_event *event)
 		this_cpu_ptr(&cpu_hw_events)->n_late_setup--;
 }
 
+int __intel_pmu_quiesce(void)
+{
+	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
+	int pmu_enabled = cpuc->enabled;
+
+	cpuc->enabled = 0;
+	if (pmu_enabled)
+		intel_pmu_disable_all();
+
+	return pmu_enabled;
+}
+
+void __intel_pmu_resume(int pmu_enabled)
+{
+	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
+
+	cpuc->enabled = pmu_enabled;
+	if (pmu_enabled)
+		intel_pmu_enable_all(0);
+}
+
 static int icl_set_topdown_event_period(struct perf_event *event)
 {
 	struct hw_perf_event *hwc = &event->hw;
@@ -3316,16 +3337,13 @@ static void intel_pmu_read_event(struct perf_event *event)
 	if (event->hw.flags & (PERF_X86_EVENT_AUTO_RELOAD | PERF_X86_EVENT_TOPDOWN) ||
 	    is_pebs_counter_event_group(event)) {
 		struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
-		bool pmu_enabled = cpuc->enabled;
+		int pmu_enabled;
 
 		/* Only need to call update_topdown_event() once for group read. */
 		if (is_metric_event(event) && (cpuc->txn_flags & PERF_PMU_TXN_READ))
 			return;
 
-		cpuc->enabled = 0;
-		if (pmu_enabled)
-			intel_pmu_disable_all();
-
+		pmu_enabled = __intel_pmu_quiesce();
 		/*
 		 * If the PEBS counters snapshotting is enabled,
 		 * the topdown event is available in PEBS records.
@@ -3334,10 +3352,7 @@ static void intel_pmu_read_event(struct perf_event *event)
 			static_call(intel_pmu_update_topdown_event)(event, NULL);
 		else
 			intel_pmu_drain_pebs_buffer();
-
-		cpuc->enabled = pmu_enabled;
-		if (pmu_enabled)
-			intel_pmu_enable_all(0);
+		__intel_pmu_resume(pmu_enabled);
 
 		return;
 	}

arch/x86/events/intel/ds.c

@@ -1242,8 +1242,11 @@ int intel_pmu_drain_bts_buffer(void)
 
 void intel_pmu_drain_pebs_buffer(void)
 {
+	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
 	struct perf_sample_data data;
 
+	WARN_ON_ONCE(cpuc->enabled);
+
 	static_call(x86_pmu_drain_pebs)(NULL, &data);
 }
 
@@ -1864,8 +1867,11 @@ static void intel_pmu_pebs_via_pt_enable(struct perf_event *event)
 static inline void intel_pmu_drain_large_pebs(struct cpu_hw_events *cpuc)
 {
 	if (cpuc->n_pebs == cpuc->n_large_pebs &&
-	    cpuc->n_pebs != cpuc->n_pebs_via_pt)
+	    cpuc->n_pebs != cpuc->n_pebs_via_pt) {
+		int enabled = __intel_pmu_quiesce();
 		intel_pmu_drain_pebs_buffer();
+		__intel_pmu_resume(enabled);
+	}
 }
 
 static void __intel_pmu_pebs_enable(struct perf_event *event)

arch/x86/events/perf_event.h

@@ -1638,6 +1638,9 @@ static __always_inline void __intel_pmu_lbr_disable(void)
 	wrmsrq(MSR_IA32_DEBUGCTLMSR, debugctl);
 }
 
+extern int __intel_pmu_quiesce(void);
+extern void __intel_pmu_resume(int pmu_enabled);
+
 int intel_pmu_save_and_restart(struct perf_event *event);
 
 struct event_constraint *