linux-kernel - Re: RFC: banning device driver reserved resources from /dev/mem

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Message-ID: <20081006070543.23b14828@infradead.org>
Date:	Mon, 6 Oct 2008 07:05:43 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Maxim Levitsky <maximlevitsky@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: RFC: banning device driver reserved resources from /dev/mem

On Mon, 6 Oct 2008 15:01:22 +0100
Alan Cox <alan@...rguk.ukuu.org.uk> wrote:

> > > Only a tiny fraction of devices in the world are PCI, and those
> > > platforms where you most what /dev/mem type debugging tools are
> > > often those without PCI
> > 
> > if you looked at the patch it's x86 only, and only active if you set
> > CONFIG_STRICT_DEVMEM.
> > (if you don't select CONFIG_STRICT_DEVMEM, which is off by default,
> > you get unlimited access as usualy)
> 
> Lots of non PCI devices on x86 systems as well.
> 
> And the video problem is a big one for the x86 case as the VGA ISA
> window is used by both the kernel and X without a helper driver.

no argument, except that the kernel doesn't do request_region() on it
to expect exclusivity (so the patch doesn't do anything on this region)

Now having said that, if the DRM layer does request_region on the MMIO
bars, we might need a flag that explicitly says "this is intended for
sharing with userspace" for this known case; not too hard, I'll check
with Dave Airlie.


-- 
Arjan van de Ven 	Intel Open Source Technology Centre
For development, discussion and tips for power savings, 
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