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

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Date:	Wed, 15 Jul 2009 18:24:46 +0900
From:	Paul Mundt <lethal@...ux-sh.org>
To:	David Howells <dhowells@...hat.com>
Cc:	Mike Frysinger <vapier@...too.org>, linux-kernel@...r.kernel.org,
	uclinux-dist-devel@...ckfin.uclinux.org,
	Bernd Schmidt <bernds_cb1@...nline.de>,
	Bryan Wu <cooloney@...nel.org>
Subject: Re: [PATCH v2] NOMMU: add support for Memory Protection Units (MPU)

On Tue, Jul 14, 2009 at 06:22:06PM +0100, 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?
> 
SH can do this as well for the single-address-space mode in the MMU, but
in that case I would still use a global page table.
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