linux-kernel - Re: [RFC PATCH 19/26] x86/alternatives: NMI safe runtime patching

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Date:   Wed, 8 Apr 2020 13:36:31 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Ankur Arora <ankur.a.arora@...cle.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org, hpa@...or.com,
        jpoimboe@...hat.com, namit@...are.com, mhiramat@...nel.org,
        jgross@...e.com, bp@...en8.de, vkuznets@...hat.com,
        pbonzini@...hat.com, boris.ostrovsky@...cle.com,
        mihai.carabas@...cle.com, kvm@...r.kernel.org,
        xen-devel@...ts.xenproject.org,
        virtualization@...ts.linux-foundation.org
Subject: Re: [RFC PATCH 19/26] x86/alternatives: NMI safe runtime patching

On Tue, Apr 07, 2020 at 10:03:16PM -0700, Ankur Arora wrote:
> @@ -1807,12 +1911,20 @@ static int __maybe_unused text_poke_late(patch_worker_t worker, void *stage)
>  	text_poke_state.state = PATCH_SYNC_DONE; /* Start state */
>  	text_poke_state.primary_cpu = smp_processor_id();
>  
> +	text_poke_state.nmi_context = nmi;
> +
> +	if (nmi)
> +		register_nmi_handler(NMI_LOCAL, text_poke_nmi,
> +				     NMI_FLAG_FIRST, "text_poke_nmi");
>  	/*
>  	 * Run the worker on all online CPUs. Don't need to do anything
>  	 * for offline CPUs as they come back online with a clean cache.
>  	 */
>  	ret = stop_machine(patch_worker, &text_poke_state, cpu_online_mask);
>  
> +	if (nmi)
> +		unregister_nmi_handler(NMI_LOCAL, "text_poke_nmi");
> +
>  	return ret;
>  }

This is completely bonghits crazy.