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Re: can read/write to mprotect(PROT_NONE) region with 2.6.14 on au1550

To: Clem Taylor <clem.taylor@gmail.com>
Subject: Re: can read/write to mprotect(PROT_NONE) region with 2.6.14 on au1550
From: Ralf Baechle <ralf@linux-mips.org>
Date: Thu, 2 Feb 2006 16:54:36 +0000
Cc: linux-mips <linux-mips@linux-mips.org>
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On Wed, Dec 07, 2005 at 04:51:23PM -0500, Clem Taylor wrote:

> I was trying to use mprotect(PROT_NONE) to help debug a problem, and
> it seems that mprotect() isn't actually doing anything with my 2.6.14
> linux-mips kernel on an au1550. Attached is a simple test program that
> segfaults as expected on x86 (2.6.12), but does not segfault on mips
> (2.6.14). I can both read and write PROT_NONE memory without problem,
> which should result in a segfault. Originally, I was trying to
> mprotect() a mmaped GFP_DMA region which wasn't working and then I
> tried a simpler test that also wasn't working.
> 
> Shouldn't mprotect() work? Could I be missing a config option, or is
> this just broken?

That's a defect in CONFIG_64BIT_PHYS_ADDR which unfortunately is need
on Alchemy SOCs due to the silly address space layout.

  Ralf

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