Re: [PATCH 00/10] Enhance /dev/mem to allow read/write of arbitrary physical addresses
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- To: Ingo Molnar <mingo@xxxxxxx>
- Subject: Re: [PATCH 00/10] Enhance /dev/mem to allow read/write of arbitrary physical addresses
- From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
- Date: Fri, 1 Jul 2011 09:47:05 -0400
- Cc: Petr Tesarik <ptesarik@xxxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, Fenghua Yu <fenghua.yu@xxxxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Paul Mundt <lethal@xxxxxxxxxxxx>, Russell King <linux@xxxxxxxxxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, Tony Luck <tony.luck@xxxxxxxxx>, x86@xxxxxxxxxx, linux-arm-kernel@xxxxxxxxxxxxxxxxxxx, linux-ia64@xxxxxxxxxxxxxxx, linux-sh@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, Arjan van de Ven <arjan@xxxxxxxxxxxxx>, Dave Jones <davej@xxxxxxxxxx>, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
- In-reply-to: <20110701125802.GE12605@elte.hu>
- List-id: <linux-ia64.vger.kernel.org>
- References: <201106171038.25988.ptesarik@suse.cz> <20110617093032.GA19235@elte.hu> <201106291106.00070.ptesarik@suse.cz> <20110701125802.GE12605@elte.hu>
- User-agent: Mutt/1.5.21 (2010-09-15)
On Fri, Jul 01, 2011 at 02:58:02PM +0200, Ingo Molnar wrote:
> So what was not mentioned in your series, what is *your* motivation
> and your usecase? Enabling closed-source userspace drivers? Enabling
> the crash utility?
He stated it pretty clearly in the thread, it's the crash utility.
>
> If the former then shame on you, if the latter then how do you
> explain that distros appear to disable the RAM aspect of /dev/mem:
>
> $ grep DEVMEM $(rpm -ql kernel-2.6.38-0.rc7.git2.3.fc16.x86_64 | grep config-2.6 )
> CONFIG_STRICT_DEVMEM=y
>
> So the crash utility use-case does not work on unpatched, default
> kernels, right?
Not if you have highmem. That's why Redhat or Fedora to quote your
example patch in the /dev/crash driver, which totally defeats the
CONFIG_STRICT_DEVMEM setting. But apparently it's good enough that no
one either noticed or at least doesn't care.
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