Re: [PATCH 6.12.y] perf/x86/intel: Don't clear perf metrics overflow bit unconditionally

On Sat, Sep 06, 2025 at 10:38:26AM -0400, Sasha Levin wrote:

From: Dapeng Mi dapeng1.mi@linux.intel.com

[ Upstream commit a5f5e1238f4ff919816f69e77d2537a48911767b ]

The below code would always unconditionally clear other status bits like perf metrics overflow bit once PEBS buffer overflows:

    status &= intel_ctrl | GLOBAL_STATUS_TRACE_TOPAPMI;

This is incorrect. Perf metrics overflow bit should be cleared only when fixed counter 3 in PEBS counter group. Otherwise perf metrics overflow could be missed to handle.

Closes: https://lore.kernel.org/all/20250225110012.GK31462@noisy.programming.kicks-a... Fixes: 7b2c05a15d29 ("perf/x86/intel: Generic support for hardware TopDown metrics") Signed-off-by: Dapeng Mi dapeng1.mi@linux.intel.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Signed-off-by: Ingo Molnar mingo@kernel.org Reviewed-by: Kan Liang kan.liang@linux.intel.com Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20250415104135.318169-1-dapeng1.mi@linux.intel.com Signed-off-by: Sasha Levin sashal@kernel.org

---

arch/x86/events/intel/core.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c index 5e43d390f7a3d..063147d7161b6 100644 --- a/arch/x86/events/intel/core.c +++ b/arch/x86/events/intel/core.c @@ -3029,7 +3029,6 @@ static int handle_pmi_common(struct pt_regs *regs, u64 status) struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events); int bit; int handled = 0;

• u64 intel_ctrl = hybrid(cpuc->pmu, intel_ctrl);

inc_irq_stat(apic_perf_irqs); @@ -3073,7 +3072,6 @@ static int handle_pmi_common(struct pt_regs *regs, u64 status) handled++; x86_pmu_handle_guest_pebs(regs, &data); static_call(x86_pmu_drain_pebs)(regs, &data);

• status &= intel_ctrl | GLOBAL_STATUS_TRACE_TOPAPMI;
  

/* * PMI throttle may be triggered, which stops the PEBS event. @@ -3084,6 +3082,15 @@ static int handle_pmi_common(struct pt_regs *regs, u64 status) */ if (pebs_enabled != cpuc->pebs_enabled) wrmsrl(MSR_IA32_PEBS_ENABLE, cpuc->pebs_enabled);

• /*
  

•  * Above PEBS handler (PEBS counters snapshotting) has updated fixed
  

•  * counter 3 and perf metrics counts if they are in counter group,
  

•  * unnecessary to update again.
  

•  */
  

• if (cpuc->events[INTEL_PMC_IDX_FIXED_SLOTS] &&
  

•     is_pebs_counter_event_group(cpuc->events[INTEL_PMC_IDX_FIXED_SLOTS]))
  

• 	status &= ~GLOBAL_STATUS_PERF_METRICS_OVF_BIT;
  

  }

/* @@ -3103,6 +3110,8 @@ static int handle_pmi_common(struct pt_regs *regs, u64 status) static_call(intel_pmu_update_topdown_event)(NULL); }

• status &= hybrid(cpuc->pmu, intel_ctrl);
• /*
  • Checkpointed counters can lead to 'spurious' PMIs because the
  • rollback caused by the PMI will have cleared the overflow status

-- 2.51.0

This breaks the build:

arch/x86/events/intel/core.c: In function ‘handle_pmi_common’: arch/x86/events/intel/core.c:3092:21: error: implicit declaration of function ‘is_pebs_counter_event_group’ [-Wimplicit-function-declaration] 3092 | is_pebs_counter_event_group(cpuc->events[INTEL_PMC_IDX_FIXED_SLOTS])) | ^~~~~~~~~~~~~~~~~~~~~~~~~~~

so I'll not apply it.

thanks,

greg k-h