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

[Greg KH <gregkh@linuxfoundation.org>]

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-ass.net/
> 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