linux-kernel - Re: UML fails to locate address space

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Message-ID: <20080520161047.GA9598@c2.user-mode-linux.org>
Date:	Tue, 20 May 2008 12:10:47 -0400
From:	Jeff Dike <jdike@...toit.com>
To:	Tom Spink <tspink@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: UML fails to locate address space

On Tue, May 20, 2008 at 02:59:14PM +0100, Tom Spink wrote:
> Attached.  I guess the line of interest is:
> 
> mmap2(NULL, 4096, PROT_READ|PROT_WRITE,
> MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = -1 EACCES (Permission
> denied)

Yup.

Can you try three things:
	check the maps file for any arbitrary process
(i.e. /proc/$$/maps) and see if there's anything mapped at 0
	gdb UML, stop it at that mmap, check its maps file and see if
there's anything mapped at 0
	send me a pointer to the patches that Ubuntu has applied on
top of the stock kernel - I'm suspicious that they special-cased page
zero in order to ensure that NULL pointer dereferences cause faults.

You can test this last theory by initializing bottom to 4096 instead
of 0.

     	      	 	Jeff

-- 
Work email - jdike at linux dot intel dot com
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