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From: David Howells <dhowells@redhat.com>
In-Reply-To: <1247591665-12000-1-git-send-email-vapier@gentoo.org>
References: <1247591665-12000-1-git-send-email-vapier@gentoo.org> <20090714161416.GA19147@cmpxchg.org>
To: Mike Frysinger <vapier@gentoo.org>
Cc: dhowells@redhat.com, linux-kernel@vger.kernel.org,
       uclinux-dist-devel@blackfin.uclinux.org,
       Bernd Schmidt <bernds_cb1@t-online.de>, Bryan Wu <cooloney@kernel.org>
Subject: Re: [PATCH v2] NOMMU: add support for Memory Protection Units (MPU)
Date: Tue, 14 Jul 2009 18:22:06 +0100
Message-ID: <6206.1247592126@redhat.com>
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 996
Lines: 21

Mike Frysinger <vapier@gentoo.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?

David
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