linux-kernel - Re: [PATCH v3 x86 1/2] fix page faults by nmiaction in nmi if kmemcheck is enabled

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Date:	Tue, 6 Mar 2012 10:00:00 -0500
From:	Don Zickus <dzickus@...hat.com>
To:	Li Zhong <zhong@...ux.vnet.ibm.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	LKML <linux-kernel@...r.kernel.org>, tglx@...utronix.de,
	mingo@...hat.com, hpa@...or.com, x86@...nel.org, paulus@...ba.org,
	mingo@...e.hu, acme@...stprotocols.net,
	Vegard Nossum <vegardno@....uio.no>, tony.luck@...el.com,
	bp@...64.org, robert.richter@....com, lenb@...nel.org,
	minyard@....org, wim@...ana.be, linux-edac@...r.kernel.org,
	oprofile-list@...ts.sf.net, linux-acpi@...r.kernel.org,
	openipmi-developer@...ts.sourceforge.net,
	linux-watchdog@...r.kernel.org
Subject: Re: [PATCH v3 x86 1/2]  fix page faults by nmiaction in nmi if
 kmemcheck is enabled

On Tue, Mar 06, 2012 at 06:09:43PM +0800, Li Zhong wrote:
> This patch tries to fix the problem of page fault exception caused by
> accessing nmiaction structure in nmi if kmemcheck is enabled. 
> 
> If kmemcheck is enabled, the memory allocated through slab are in pages
> that are marked non-present, so that some checks could be done in the
> page fault handling code ( e.g. whether the memory is read before
> written to ). 
> As nmiaction is allocated in this way, so it resides in a non-present
> page. Then there is a page fault while the nmi code accessing the
> nmiaction structure, which would then cause a warning by
> WARN_ON_ONCE(in_nmi()) in kmemcheck_fault(), called by do_page_fault().
> 
> v2: as Peter suggested, changed the nmiaction to use static storage.
> 
> v3: as Peter suggested, use macro to shorten the codes. Also keep the
> original usage of register_nmi_handler, so users of this call doesn't
> need change. 

Thanks Li!  Looks fine to me.  I'll run some tests to make sure things
still work correctly.

Cheers,
Don
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