linux-kernel - Re: /dev/mem "unbounded?"

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Message-ID: <1927751307.356328.1320878326756.JavaMail.root@zimbra-prod-mbox-2.vmware.com>
Date:	Wed, 9 Nov 2011 14:38:46 -0800 (PST)
From:	Andrei Warkentin <awarkentin@...are.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: /dev/mem "unbounded?"

Hi Peter,

----- Original Message -----
> 
> That would be incorrect behavior, though, except perhaps for the
> range
> that cannot be addressed by the processor.  It is explicitly
> permitted
> to address ranges that does not have addresses mapped to it.

There is a current mechanism for restricting access to a subset
of addresses, and it is used to enforce < 1MB accesses on x86
if CONFIG_STRICT_DEVMEM. This could be extended.

Do you think there is any value in specifying something like
CONFIG_DEV_MEM_ONLY_CLAIMED, which would only allow accesses
until the end of the last range claimed with request_region (but
could, of course, well be unmapped). This will allow accesses to
any unclaimed "holes" in between. I.e., if you have 0-100m claimed,
followed by 300-700m claimed, then reading /dev/mem will work up
until you reach 700m.

> 
> -EFAULT would also be wrong.  If anything it should be -EIO.
> 

Ok, I'll submit a patch for that.

A
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