linux-kernel - Re: [PATCH 00/10] Enhance /dev/mem to allow read/write of arbitrary physical addresses

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Date:	Sun, 3 Jul 2011 21:46:18 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Petr Tesarik <ptesarik@...e.cz>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Christoph Hellwig <hch@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Fenghua Yu <fenghua.yu@...el.com>,
	Ingo Molnar <mingo@...hat.com>,
	Paul Mundt <lethal@...ux-sh.org>,
	Russell King <linux@....linux.org.uk>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tony Luck <tony.luck@...el.com>, x86@...nel.org,
	linux-arm-kernel@...ts.infradead.org, linux-ia64@...r.kernel.org,
	linux-sh@...r.kernel.org, linux-kernel@...r.kernel.org,
	Arjan van de Ven <arjan@...radead.org>,
	Dave Jones <davej@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 00/10] Enhance /dev/mem to allow read/write of arbitrary
 physical addresses


* Petr Tesarik <ptesarik@...e.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
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