linux-kernel - Re: [PATCH -tip] perf, x86: fix unknown NMIs on a Pentium4 box

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Date:	Thu, 14 Apr 2011 23:43:25 +0400
From:	Cyrill Gorcunov <gorcunov@...nvz.org>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Don Zickus <dzickus@...hat.com>, Lin Ming <ming.m.lin@...el.com>,
	Shaun Ruffell <sruffell@...ium.com>,
	Maciej Rutecki <maciej.rutecki@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Stephane Eranian <eranian@...gle.com>,
	Robert Richter <robert.richter@....com>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -tip] perf, x86: fix unknown NMIs on a Pentium4 box

On 04/14/2011 10:46 PM, Ingo Molnar wrote:
> 
> btw., the bug went away once i removed your patch so it's 100% sure caused by 
> this change.
> 
> Thanks,
> 
> 	Ingo

Ingo if you have a chance mind to give this patch a shot please? Seems we might miss unmasking
for inflight nmis.
-- 
Index: linux-2.6.git/arch/x86/kernel/cpu/perf_event.c
=====================================================================
--- linux-2.6.git.orig/arch/x86/kernel/cpu/perf_event.c
+++ linux-2.6.git/arch/x86/kernel/cpu/perf_event.c
@@ -1365,14 +1365,15 @@ perf_event_nmi_handler(struct notifier_b
 		 * will be empty and daze the CPU. So, we drop it to
 		 * avoid false-positive 'unknown nmi' messages.
 		 */
+		apic_write(APIC_LVTPC, APIC_DM_NMI);
 		return NOTIFY_STOP;
 	default:
 		return NOTIFY_DONE;
 	}

-	apic_write(APIC_LVTPC, APIC_DM_NMI);

 	handled = x86_pmu.handle_irq(args->regs);
+	apic_write(APIC_LVTPC, APIC_DM_NMI);
 	if (!handled)
 		return NOTIFY_DONE;

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