Re: [Patch v3 5/8] perf/x86/intel: Validate the return value of intel_pmu_init_hybrid()

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Relocating `intel_pmu_arch_lbr_init()` below `intel_pmu_check_event_constraints_all()` bypasses the dynamic constraint validation for branch counters.
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commit 4ceb25a65fdf63fe8fa33e932139cf0a5d28e924
Author: Dapeng Mi <dapeng1.mi@linux.intel.com>

perf/x86/intel: Validate the return value of intel_pmu_init_hybrid()

This patch validates the return value of intel_pmu_init_hybrid() to avoid a
null-pointer dereference. It also defers intel_pmu_arch_lbr_init() until after
hybrid PMU initialization succeeds to avoid destroying the kmem cache on
failure.

> diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
> index db52e7e53a6cd..74dbf24b0ab63 100644
> --- a/arch/x86/events/intel/core.c
> +++ b/arch/x86/events/intel/core.c
[ ... ]
> @@ -8829,6 +8842,9 @@ __init int intel_pmu_init(void)
>  
>  	intel_pmu_check_event_constraints_all(NULL);
>  
> +	if (boot_cpu_has(X86_FEATURE_ARCH_LBR))
> +		intel_pmu_arch_lbr_init();
> +
[Severity: Medium]
Does moving intel_pmu_arch_lbr_init() below
intel_pmu_check_event_constraints_all() bypass the dynamic constraint
validation for branch counters?

When intel_pmu_check_event_constraints_all() runs, it eventually calls
intel_pmu_check_dyn_constr(). This check relies on the PMU_FL_BR_CNTR flag
and the x86_pmu.lbr_counters mask:

arch/x86/events/intel/core.c:intel_pmu_check_dyn_constr() {
    ...
		case DYN_CONSTR_BR_CNTR:
			if (x86_pmu.flags & PMU_FL_BR_CNTR)
				mask = x86_pmu.lbr_counters;
			break;
    ...
}

Because intel_pmu_arch_lbr_init() is now deferred until after this validation,
the PMU_FL_BR_CNTR flag hasn't been set yet. Will this cause the dynamic
constraint check for branch counters to evaluate to false and be skipped?

>  	/*
>  	 * Access LBR MSR may cause #GP under certain circumstances.
>  	 * Check all LBR MSR here.

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Sashiko AI review · https://sashiko.dev/#/patchset/20260612090114.3188886-1-dapeng1.mi@linux.intel.com?part=5