Re: [PATCH v4 8/9] x86/nmi: Simplify offline microcode handler invocation

[Chang S. Bae]

On 11/4/2026 10:23 AM, Chang S. Bae wrote:
> diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c
> index e3660b8b8f38..11c965445bdc 100644
> --- a/arch/x86/kernel/nmi.c
> +++ b/arch/x86/kernel/nmi.c
> @@ -553,7 +553,7 @@ DEFINE_IDTENTRY_RAW(exc_nmi)
>   		raw_atomic_long_inc(&nsp->idt_calls);
>   
>   	if (arch_cpu_is_offline(smp_processor_id())) {
> -		if (microcode_nmi_handler_enabled())
> +		if (IS_ENABLED(CONFIG_MICROCODE_LATE_LOADING))
>   			microcode_offline_nmi_handler();
>   		return;
>   	}
> @@ -715,7 +715,7 @@ DEFINE_FREDENTRY_NMI(exc_nmi)
>   	irqentry_state_t irq_state;
>   
>   	if (arch_cpu_is_offline(smp_processor_id())) {
> -		if (microcode_nmi_handler_enabled())
> +		if (IS_ENABLED(CONFIG_MICROCODE_LATE_LOADING))
>   			microcode_offline_nmi_handler();
>   		return;
>   	}

There is a Sashiko comment on this:
https://sashiko.dev/#/patchset/20261104182322.578066-1-chang.seok.bae%40intel.com

I thought waking up soft-offlined SMT siblings with an NMI was benign. 
Right now the path is not explicitly gated by the use_nmi flag even 
though the underlying mechanism is NMI-based.

So perhaps it's better to have this reassurance ahead:

diff --git a/arch/x86/kernel/cpu/microcode/core.c 
b/arch/x86/kernel/cpu/microcode/core.c
index 330c62f6dd32..cf3c02622dc1 100644
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -502,8 +502,11 @@ static void load_primary(unsigned int cpu)
        unsigned int nr_offl = cpumask_weight(&cpu_offline_mask);
        bool proceed = true;

-       /* Kick soft-offlined SMT siblings if required */
-       if (!cpu && nr_offl)
+       /*
+        * Kick soft-offlined SMT siblings if required.
+        * Note the mechanism is NMI base.
+        */
+       if (microcode_ops->use_nmi && !cpu && nr_offl)
                proceed = kick_offline_cpus(nr_offl);

        /* If the soft-offlined CPUs did not respond, abort */
@@ -511,7 +514,7 @@ static void load_primary(unsigned int cpu)
                __load_primary(cpu);

        /* Unconditionally release soft-offlined SMT siblings if 
required */
-       if (!cpu && nr_offl)
+       if (microcode_ops->use_nmi && !cpu && nr_offl)
                release_offline_cpus();
 }

Thanks,
Chang