linux-kernel - Re: x86: Allow vmalloc faults from NMI context

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Message-ID: <20140410154051.4d709272@gandalf.local.home>
Date:	Thu, 10 Apr 2014 15:40:51 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Jiri Olsa <jolsa@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org
Subject: Re: x86: Allow vmalloc faults from NMI context

On Thu, 10 Apr 2014 16:40:03 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> Jiri reported he hit vmalloc_faults()'s:
> 
>   WARN_ON_ONCE(in_nmi());
> 
> The patch that added this ebc8827f75954 ("x86: Barf when vmalloc and
> kmemcheck faults happen in NMI") explains that this was done in order to
> avoid faults from NMI to cause nested NMIs.
> 
> We have, however, completely fixed this issue and can now safely take
> faults from NMI context.
> 
> Therefore remove this warning. We must still leave the kmemcheck warn in
> place since kmemcheck itself can't deal with NMI context yet.
> 

Yay, finally....

Link: http://lkml.kernel.org/p/20131015163906.342d8ffa@gandalf.local.home

-- Steve

> Signed-off-by: Peter Zijlstra <peterz@...radead.org>
> ---
>  arch/x86/mm/fault.c | 4 ----
>  1 file changed, 4 deletions(-)
> 
> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> index 8e5722992677..d0234cdf70f1 100644
> --- a/arch/x86/mm/fault.c
> +++ b/arch/x86/mm/fault.c
> @@ -271,8 +271,6 @@ static noinline __kprobes int vmalloc_fault(unsigned long address)
>  	if (!(address >= VMALLOC_START && address < VMALLOC_END))
>  		return -1;
>  
> -	WARN_ON_ONCE(in_nmi());
> -
>  	/*
>  	 * Synchronize this task's top level page-table
>  	 * with the 'reference' page table.
> @@ -369,8 +367,6 @@ static noinline __kprobes int vmalloc_fault(unsigned long address)
>  	if (!(address >= VMALLOC_START && address < VMALLOC_END))
>  		return -1;
>  
> -	WARN_ON_ONCE(in_nmi());
> -
>  	/*
>  	 * Copy kernel mappings over when needed. This can also
>  	 * happen within a race in page table update. In the later

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