linux-kernel - Re: [RFC][PATCH] nmi watchdog: handle NMI_IO_APIC on nmi

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Message-ID: <20081022215008.GE28317@cathedrallabs.org>
Date:	Wed, 22 Oct 2008 17:50:08 -0400
From:	Aristeu Rozanski <aris@...vo.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Vivek Goyal <vgoyal@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH] nmi watchdog: handle NMI_IO_APIC on nmi_watchdog

> > > stop_apic_nmi_watchdog() doesnt currently properly disable the 
> > > generation of NMIs when they come from an IO-APIC, so this will need 
> > > more fixes i believe. One approach would be to save the IO-APIC id and 
> > > pin when the watchdog is set up, and use it later on to poke that 
> > > IO-APIC register to disable NMI generation there.
> > the patch I sent has this change:
> > 
> > @@ -270,6 +270,8 @@ void stop_apic_nmi_watchdog(void *unused
> >                 return;
> >         if (nmi_watchdog == NMI_LOCAL_APIC)
> >                 lapic_watchdog_stop();
> > +       else
> > +               __acpi_nmi_disable(NULL);
> >         __get_cpu_var(wd_enabled) = 0;
> >         atomic_dec(&nmi_active);
> >  }
> > 
> > and:
> > static void __acpi_nmi_disable(void *__unused)
> > {       
> >         apic_write(APIC_LVT0, APIC_DM_NMI | APIC_LVT_MASKED);
> > }
> > 
> > do you think this isn't enough?
> 
> but this stops all NMIs, not just the IO-APIC generated ones, doesnt it? 
external NMIs would come by LINT1, no?
after reading a lot and talking with Vivek, what I understood was that 8259 is
also connected to LINT0, so timer interrupts would be reported both in
IOAPIC and on LINT0. LVT0 is being configured on setup_nmi() to generate
an NMI. Also, the same timer interrupt would generate an regular interrupt
coming from IOAPIC. Clearing the APIC_DM_NMI on LVT0 would disable the
NMI delivery, but not the regular interrupt.
or am I missing something here?

-- 
Aristeu

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