linux-kernel - Re: [PATCH v2] x86,nmi: Fix page faults by nmiaction if kmemcheck is enabled

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Date:	Thu, 08 Mar 2012 22:04:34 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Don Zickus <dzickus@...hat.com>
Cc:	x86@...nel.org, LKML <linux-kernel@...r.kernel.org>,
	Li Zhong <zhong@...ux.vnet.ibm.com>
Subject: Re: [PATCH v2] x86,nmi: Fix page faults by nmiaction if kmemcheck
 is enabled

On Thu, 2012-03-08 at 16:02 -0500, Don Zickus wrote:
> From: Li Zhong <zhong@...ux.vnet.ibm.com>
> 
> 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.
> 
> [simplified wrappers -dcz]
> 
> Signed-off-by: Li Zhong <zhong@...ux.vnet.ibm.com>
> Signed-off-by: Don Zickus <dzickus@...hat.com> 

Thanks!

Acked-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
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