linux-kernel - Re: [PATCH v2] NOMMU: add support for Memory Protection Units (MPU)

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Message-ID: <4A5CFFD8.7020106@t-online.de>
Date:	Tue, 14 Jul 2009 22:59:52 +0100
From:	Bernd Schmidt <bernds_cb1@...nline.de>
To:	David Howells <dhowells@...hat.com>
CC:	Mike Frysinger <vapier@...too.org>, linux-kernel@...r.kernel.org,
	uclinux-dist-devel@...ckfin.uclinux.org,
	Bryan Wu <cooloney@...nel.org>
Subject: Re: [PATCH v2] NOMMU: add support for Memory Protection Units (MPU)

David Howells wrote:
> Mike Frysinger <vapier@...too.org> wrote:
> 
>> Some architectures (like the Blackfin arch) implement some of the
>> "simpler" features that one would expect out of a MMU such as memory
>> protection.  In our case, we actually get read/write/exec protection
>> down to the page boundary so processes can't stomp on each other let
>> alone the kernel.  There is a performance decrease (which depends greatly
>> on the workload) however as the hardware/software interaction was not
>> optimized at design time.
> 
> It occurs to me that I could probably test this on FRV by using the MMU in a
> limited way.  How do you actually keep track of the protections applied?  Do
> you have a single global page table that is managed by the mmap code on a
> per-VMA basis?

No page table, just three bitmaps (r/w/x), with one bit per page, per mm.


Bernd
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