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Date: Sun, 3 Jul 2011 21:46:18 +0200
From: Ingo Molnar <mingo@elte.hu>
To: Petr Tesarik <ptesarik@suse.cz>
Cc: "H. Peter Anvin" <hpa@zytor.com>, Christoph Hellwig <hch@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Fenghua Yu <fenghua.yu@intel.com>, Ingo Molnar <mingo@redhat.com>,
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        Dave Jones <davej@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH 00/10] Enhance /dev/mem to allow read/write of arbitrary
 physical addresses
Message-ID: <20110703194618.GB27022@elte.hu>
References: <201106171038.25988.ptesarik@suse.cz>
 <201107012134.45881.ptesarik@suse.cz>
 <20110701195629.GA19057@elte.hu>
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* Petr Tesarik <ptesarik@suse.cz> wrote:

> > Do you expect distros to enable this boot option by default? I.e. 
> > would SuSE be willing to ship with a restrictive /dev/mem by 
> > default? That's really the wider goal we want to work towards.
> 
> I'm not really the decision-maker on this, but even though I don't 
> need it for crash, there are several other users which would have 
> to be fixed:
> 
> 1. hwinfo (EFI, MPTABLE and ACPI table parsing, analyzing video BIOS)
> 2. dmidecode (SMBIOS, DMI)
> 3. possibly others

But those tables wont be in regular RAM (they will be in ROM or in 
RAM marked non-RAM in a special way in the e820 tables).

dmidecode certainly works on Fedora.

> > Hm, why would the ability "dirty and/or flush an arbitrary 
> > physical cache line for testing purposes" be a DoS?
> 
> Effectively switching off CPU caches can slow things down quite a 
> bit... especially on a large SMP system. ;)

Flushing a cacheline isnt switching it off. You can already 'flush' 
the cache from user-space as well, by trashing it for example. So i 
don't see the DoS angle.

Thanks,

	Ingo