[Patch v7 23/24] perf/x86: Activate back-to-back NMI detection for arch-PEBS induced NMIs

Dapeng Mi
2026-03-24T00:47:40Z

When two or more identical PEBS events with the same sampling period are
programmed on a mix of PDIST and non-PDIST counters, multiple
back-to-back NMIs can be triggered.

The Linux PMI handler processes the first NMI and clears the
GLOBAL_STATUS MSR. If a second NMI is triggered immediately after
the first, it is recognized as a "suspicious NMI" because no bits are set
in the GLOBAL_STATUS MSR (cleared by the first NMI).

This issue does not lead to PEBS data corruption or data loss, but it
does result in an annoying warning message.

The current NMI handler supports back-to-back NMI detection, but it
requires the PMI handler to return the count of actually processed events,
which the PEBS handler does not currently do.

This patch modifies the PEBS handlers to return the count of actually
processed events, thereby activating back-to-back NMI detection and
avoiding the "suspicious NMI" warning.

Suggested-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
---
arch/x86/events/intel/core.c | 6 ++----
arch/x86/events/intel/ds.c | 40 ++++++++++++++++++++++++------------
arch/x86/events/perf_event.h | 2 +-
3 files changed, 30 insertions(+), 18 deletions(-)

diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index e0dd57906bca..9da0a1354045 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -3558,9 +3558,8 @@ static int handle_pmi_common(struct pt_regs *regs, u64 status)
if (__test_and_clear_bit(GLOBAL_STATUS_BUFFER_OVF_BIT, (unsigned long *)&status)) {
u64 pebs_enabled = cpuc->pebs_enabled;

- handled++;
x86_pmu_handle_guest_pebs(regs, &data);
- static_call(x86_pmu_drain_pebs)(regs, &data);
+ handled += static_call(x86_pmu_drain_pebs)(regs, &data);

/*
* PMI throttle may be triggered, which stops the PEBS event.
@@ -3587,8 +3586,7 @@ static int handle_pmi_common(struct pt_regs *regs, u64 status)
*/
if (__test_and_clear_bit(GLOBAL_STATUS_ARCH_PEBS_THRESHOLD_BIT,
(unsigned long *)&status)) {
- handled++;
- static_call(x86_pmu_drain_pebs)(regs, &data);
+ handled += static_call(x86_pmu_drain_pebs)(regs, &data);

if (cpuc->events[INTEL_PMC_IDX_FIXED_SLOTS] &&
is_pebs_counter_event_group(cpuc->events[INTEL_PMC_IDX_FIXED_SLOTS]))
diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c
index 4743bdfb4ed4..6e1c516122c0 100644
--- a/arch/x86/events/intel/ds.c
+++ b/arch/x86/events/intel/ds.c
@@ -3035,7 +3035,7 @@ __intel_pmu_pebs_events(struct perf_event *event,
__intel_pmu_pebs_last_event(event, iregs, regs, data, at, count, setup_sample);
}

-static void intel_pmu_drain_pebs_core(struct pt_regs *iregs, struct perf_sample_data *data)
+static int intel_pmu_drain_pebs_core(struct pt_regs *iregs, struct perf_sample_data *data)
{
struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
struct debug_store *ds = cpuc->ds;
@@ -3044,7 +3044,7 @@ static void intel_pmu_drain_pebs_core(struct pt_regs *iregs, struct perf_sample_
int n;

if (!x86_pmu.pebs_active)
- return;
+ return 0;

at = (struct pebs_record_core *)(unsigned long)ds->pebs_buffer_base;
top = (struct pebs_record_core *)(unsigned long)ds->pebs_index;
@@ -3055,22 +3055,24 @@ static void intel_pmu_drain_pebs_core(struct pt_regs *iregs, struct perf_sample_
ds->pebs_index = ds->pebs_buffer_base;

if (!test_bit(0, cpuc->active_mask))
- return;
+ return 0;

WARN_ON_ONCE(!event);

if (!event->attr.precise_ip)
- return;
+ return 0;

n = top - at;
if (n <= 0) {
if (event->hw.flags & PERF_X86_EVENT_AUTO_RELOAD)
intel_pmu_save_and_restart_reload(event, 0);
- return;
+ return 0;
}

__intel_pmu_pebs_events(event, iregs, data, at, top, 0, n,
setup_pebs_fixed_sample_data);
+
+ return 1; /* PMC0 only*/
}

static void intel_pmu_pebs_event_update_no_drain(struct cpu_hw_events *cpuc, u64 mask)
@@ -3093,7 +3095,7 @@ static void intel_pmu_pebs_event_update_no_drain(struct cpu_hw_events *cpuc, u64
}
}

-static void intel_pmu_drain_pebs_nhm(struct pt_regs *iregs, struct perf_sample_data *data)
+static int intel_pmu_drain_pebs_nhm(struct pt_regs *iregs, struct perf_sample_data *data)
{
struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
struct debug_store *ds = cpuc->ds;
@@ -3102,11 +3104,12 @@ static void intel_pmu_drain_pebs_nhm(struct pt_regs *iregs, struct perf_sample_d
short counts[INTEL_PMC_IDX_FIXED + MAX_FIXED_PEBS_EVENTS] = {};
short error[INTEL_PMC_IDX_FIXED + MAX_FIXED_PEBS_EVENTS] = {};
int max_pebs_events = intel_pmu_max_num_pebs(NULL);
+ u64 events_bitmap = 0;
int bit, i, size;
u64 mask;

if (!x86_pmu.pebs_active)
- return;
+ return 0;

base = (struct pebs_record_nhm *)(unsigned long)ds->pebs_buffer_base;
top = (struct pebs_record_nhm *)(unsigned long)ds->pebs_index;
@@ -3122,7 +3125,7 @@ static void intel_pmu_drain_pebs_nhm(struct pt_regs *iregs, struct perf_sample_d

if (unlikely(base >= top)) {
intel_pmu_pebs_event_update_no_drain(cpuc, mask);
- return;
+ return 0;
}

for (at = base; at < top; at += x86_pmu.pebs_record_size) {
@@ -3186,6 +3189,7 @@ static void intel_pmu_drain_pebs_nhm(struct pt_regs *iregs, struct perf_sample_d
if ((counts[bit] == 0) && (error[bit] == 0))
continue;

+ events_bitmap |= bit;
event = cpuc->events[bit];
if (WARN_ON_ONCE(!event))
continue;
@@ -3207,6 +3211,8 @@ static void intel_pmu_drain_pebs_nhm(struct pt_regs *iregs, struct perf_sample_d
setup_pebs_fixed_sample_data);
}
}
+
+ return hweight64(events_bitmap);
}

static __always_inline void
@@ -3262,7 +3268,7 @@ __intel_pmu_handle_last_pebs_record(struct pt_regs *iregs,

static DEFINE_PER_CPU(struct x86_perf_regs, x86_pebs_regs);

-static void intel_pmu_drain_pebs_icl(struct pt_regs *iregs, struct perf_sample_data *data)
+static int intel_pmu_drain_pebs_icl(struct pt_regs *iregs, struct perf_sample_data *data)
{
short counts[INTEL_PMC_IDX_FIXED + MAX_FIXED_PEBS_EVENTS] = {};
void *last[INTEL_PMC_IDX_FIXED + MAX_FIXED_PEBS_EVENTS];
@@ -3272,10 +3278,11 @@ static void intel_pmu_drain_pebs_icl(struct pt_regs *iregs, struct perf_sample_d
struct pt_regs *regs = &perf_regs->regs;
struct pebs_basic *basic;
void *base, *at, *top;
+ u64 events_bitmap = 0;
u64 mask;

if (!x86_pmu.pebs_active)
- return;
+ return 0;

base = (struct pebs_basic *)(unsigned long)ds->pebs_buffer_base;
top = (struct pebs_basic *)(unsigned long)ds->pebs_index;
@@ -3288,7 +3295,7 @@ static void intel_pmu_drain_pebs_icl(struct pt_regs *iregs, struct perf_sample_d

if (unlikely(base >= top)) {
intel_pmu_pebs_event_update_no_drain(cpuc, mask);
- return;
+ return 0;
}

if (!iregs)
@@ -3303,6 +3310,7 @@ static void intel_pmu_drain_pebs_icl(struct pt_regs *iregs, struct perf_sample_d
continue;

pebs_status = mask & basic->applicable_counters;
+ events_bitmap |= pebs_status;
__intel_pmu_handle_pebs_record(iregs, regs, data, at,
pebs_status, counts, last,
setup_pebs_adaptive_sample_data);
@@ -3310,9 +3318,11 @@ static void intel_pmu_drain_pebs_icl(struct pt_regs *iregs, struct perf_sample_d

__intel_pmu_handle_last_pebs_record(iregs, regs, data, mask, counts, last,
setup_pebs_adaptive_sample_data);
+
+ return hweight64(events_bitmap);
}

-static void intel_pmu_drain_arch_pebs(struct pt_regs *iregs,
+static int intel_pmu_drain_arch_pebs(struct pt_regs *iregs,
struct perf_sample_data *data)
{
short counts[INTEL_PMC_IDX_FIXED + MAX_FIXED_PEBS_EVENTS] = {};
@@ -3322,13 +3332,14 @@ static void intel_pmu_drain_arch_pebs(struct pt_regs *iregs,
struct x86_perf_regs *perf_regs = this_cpu_ptr(&x86_pebs_regs);
struct pt_regs *regs = &perf_regs->regs;
void *base, *at, *top;
+ u64 events_bitmap = 0;
u64 mask;

rdmsrq(MSR_IA32_PEBS_INDEX, index.whole);

if (unlikely(!index.wr)) {
intel_pmu_pebs_event_update_no_drain(cpuc, X86_PMC_IDX_MAX);
- return;
+ return 0;
}

base = cpuc->pebs_vaddr;
@@ -3367,6 +3378,7 @@ static void intel_pmu_drain_arch_pebs(struct pt_regs *iregs,

basic = at + sizeof(struct arch_pebs_header);
pebs_status = mask & basic->applicable_counters;
+ events_bitmap |= pebs_status;
__intel_pmu_handle_pebs_record(iregs, regs, data, at,
pebs_status, counts, last,
setup_arch_pebs_sample_data);
@@ -3386,6 +3398,8 @@ static void intel_pmu_drain_arch_pebs(struct pt_regs *iregs,
__intel_pmu_handle_last_pebs_record(iregs, regs, data, mask,
counts, last,
setup_arch_pebs_sample_data);
+
+ return hweight64(events_bitmap);
}

static void __init intel_arch_pebs_init(void)
diff --git a/arch/x86/events/perf_event.h b/arch/x86/events/perf_event.h
index 36688d28407f..e6bf786728eb 100644
--- a/arch/x86/events/perf_event.h
+++ b/arch/x86/events/perf_event.h
@@ -1014,7 +1014,7 @@ struct x86_pmu {
int pebs_record_size;
int pebs_buffer_size;
u64 pebs_events_mask;
- void (*drain_pebs)(struct pt_regs *regs, struct perf_sample_data *data);
+ int (*drain_pebs)(struct pt_regs *regs, struct perf_sample_data *data);
struct event_constraint *pebs_constraints;
void (*pebs_aliases)(struct perf_event *event);
u64 (*pebs_latency_data)(struct perf_event *event, u64 status);
--
2.34.1