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From: Neil Horman <nhorman@tuxdriver.com>
To: Ingo Molnar <mingo@elte.hu>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>,
	"H. Peter Anvin" <hpa@zytor.com>, Vivek Goyal <vgoyal@redhat.com>,
	tglx@linutronix.de, mingo@redhat.com, kexec@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH], issue EOI to APIC prior to calling crash_kexec in die_nmi path
Date: Fri, 8 Feb 2008 11:14:22 -0500	[thread overview]
Message-ID: <20080208161422.GA32204@hmsreliant.think-freely.org> (raw)
In-Reply-To: <20080207122404.GA8195@elte.hu>

On Thu, Feb 07, 2008 at 01:24:04PM +0100, Ingo Molnar wrote:
> 
> * Neil Horman <nhorman@tuxdriver.com> wrote:
> 
> > Ingo noted a few posts down the nmi_exit doesn't actually write to the 
> > APIC EOI register, so yeah, I agree, its bogus (and I apologize, I 
> > should have checked that more carefully).  Nevertheless, this patch 
> > consistently allowed a hangning machine to boot through an Nmi lockup.  
> > So I'm forced to wonder whats going on then that this patch helps 
> > with.  perhaps its a just a very fragile timing issue, I'll need to 
> > look more closely.
> 
> try a dummy iret, something like:
> 
>   asm volatile ("pushf; push $1f; iret; 1: \n");
> 
> to get the CPU out of its 'nested NMI' state. (totally untested)
> 
> the idea is to push down an iret frame to the kernel stack that will 
> just jump to the next instruction and gets it out of the NMI nesting. 
> Note: interrupts will/must still be disabled, despite the iret. (the 
> ordering of the pushes might be wrong, we might need more than that for 
> a valid iret, etc. etc.)
> 
> 	Ingo

Just tried this experiment and it met with success.  Executing a dummy iret
instruction got us to boot the kdump kernel successfully.  

Thoughts on how we should handle this from here?


Regards
Neil

-- 
/****************************************************
 * Neil Horman <nhorman@tuxdriver.com>
 * Software Engineer, Red Hat
 ****************************************************/

  parent reply	other threads:[~2008-02-08 16:16 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-02-06 19:25 Neil Horman
2008-02-06 19:40 ` Vivek Goyal
2008-02-06 20:12   ` Neil Horman
2008-02-06 20:21     ` H. Peter Anvin
2008-02-06 21:04       ` Neil Horman
2008-02-06 20:35     ` Vivek Goyal
2008-02-06 22:00 ` Ingo Molnar
2008-02-06 22:48   ` Vivek Goyal
2008-02-06 22:53     ` Ingo Molnar
2008-02-06 22:56     ` H. Peter Anvin
2008-02-06 23:36       ` Ingo Molnar
2008-02-06 23:50         ` Vivek Goyal
2008-02-07  0:31         ` Eric W. Biederman
2008-02-07  0:39           ` Ingo Molnar
2008-02-07  1:30             ` Eric W. Biederman
2008-02-07 12:17           ` Neil Horman
2008-02-07 12:24             ` Ingo Molnar
2008-02-07 20:37               ` Neil Horman
2008-02-08 16:14               ` Neil Horman [this message]
2008-02-08 16:45                 ` Vivek Goyal
2008-02-08 17:26                   ` Neil Horman
2008-02-12 21:08                   ` Neil Horman
2008-02-15 14:02                     ` Eric W. Biederman
2008-02-20 14:57                     ` Neil Horman
2008-02-08 16:54               ` Andi Kleen

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