linux-kernel - Re: [PATCH] kmemleak: Ignore the aperture memory hole on x86

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Message-ID: <20090815141716.GA15941@elte.hu>
Date:	Sat, 15 Aug 2009 16:17:16 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Catalin Marinas <catalin.marinas@....com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kmemleak: Ignore the aperture memory hole on x86_64


* Catalin Marinas <catalin.marinas@....com> wrote:

> This block is allocated with alloc_bootmem() and scanned by 
> kmemleak but the kernel direct mapping may no longer exist. This 
> patch tells kmemleak to ignore this memory hole.
> 
> Signed-off-by: Catalin Marinas <catalin.marinas@....com>
> Cc: Ingo Molnar <mingo@...e.hu>
> ---
>  arch/x86/kernel/aperture_64.c |    5 +++++
>  1 files changed, 5 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/x86/kernel/aperture_64.c b/arch/x86/kernel/aperture_64.c
> index 676debf..cb690b3 100644
> --- a/arch/x86/kernel/aperture_64.c
> +++ b/arch/x86/kernel/aperture_64.c
> @@ -94,6 +94,11 @@ static u32 __init allocate_aperture(void)
>  	 * code for safe
>  	 */
>  	p = __alloc_bootmem_nopanic(aper_size, aper_size, 512ULL<<20);
> +	/*
> +	 * Kmemleak should not scan this block as it may not be mapped via the
> +	 * kernel direct mapping.
> +	 */
> +	kmemleak_ignore(p);

More importantly, kmemleak should _never_ do the garbage collection 
scan for device memory (such as the agp aperture above). All the 
aperture areas are in that category - PCI aperture, IOMMU areas, 
etc. etc.

Please double check that kmemleak does not check those - there are 
devices where pure reading of that address space can have 
side-effects.

	Ingo
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