linux-kernel - Re: [PATCH] x86: introduce /dev/mem restrictions with a config option

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Message-Id: <200801311402.46833.jbarnes@virtuousgeek.org>
Date:	Thu, 31 Jan 2008 14:02:46 -0800
From:	Jesse Barnes <jbarnes@...tuousgeek.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Arjan van de Ven <arjan@...radead.org>,
	Jan Engelhardt <jengelh@...putergmbh.de>,
	linux-kernel@...r.kernel.org, davej@...hat.com, mingo@...e.hu,
	tglx@...x.de
Subject: Re: [PATCH] x86: introduce /dev/mem restrictions with a config option

On Thursday, January 31, 2008 9:42 am H. Peter Anvin wrote:
> Arjan van de Ven wrote:
> > On Thu, 31 Jan 2008 17:53:04 +0100 (CET)
> >
> > Jan Engelhardt <jengelh@...putergmbh.de> wrote:
> >> On Jan 30 2008 12:48, Arjan van de Ven wrote:
> >>> Subject: [PATCH] x86: introduce /dev/mem restrictions with a
> >>> config option
> >>>
> >>> This patch introduces a restriction on /dev/mem: Only non-memory
> >>> can be read or written unless the newly introduced config option
> >>> is set.
> >>
> >> Would not it be nicer to add a /dev/pcimem that implements the
> >> given restrictive semantics?
> >>
> >> Maybe it's just wishful thinking, but I am dreaming of an
> >> unprivileged X, and /dev/pcimem (owned by an 'x11' user or so)
> >> would be a step in that direction.
> >
> > /dev/pcimem is wrong; X can use the exact bar in sysfs already.
> > This is more for compatibility with legacy X
>
> Legacy X, and non-BAR X memory (originally ISA, of course; now
> probably more often "stolen system memory").

For legacy memory, we actually have /sys/bus/pci/<busno>/legacy_mem 
(though ia64 may be the only supported platform).  It's actually 
required on some arches due to the way this space is allocated across 
the system.

Jesse
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