Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755880AbZGNVAg (ORCPT ); Tue, 14 Jul 2009 17:00:36 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755298AbZGNVAf (ORCPT ); Tue, 14 Jul 2009 17:00:35 -0400 Received: from mailout11.t-online.de ([194.25.134.85]:58110 "EHLO mailout11.t-online.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755100AbZGNVAf (ORCPT ); Tue, 14 Jul 2009 17:00:35 -0400 Message-ID: <4A5CFFD8.7020106@t-online.de> Date: Tue, 14 Jul 2009 22:59:52 +0100 From: Bernd Schmidt User-Agent: Thunderbird 2.0.0.22 (X11/20090709) MIME-Version: 1.0 To: David Howells CC: Mike Frysinger , linux-kernel@vger.kernel.org, uclinux-dist-devel@blackfin.uclinux.org, Bryan Wu Subject: Re: [PATCH v2] NOMMU: add support for Memory Protection Units (MPU) References: <1247591665-12000-1-git-send-email-vapier@gentoo.org> <20090714161416.GA19147@cmpxchg.org> <6206.1247592126@redhat.com> In-Reply-To: <6206.1247592126@redhat.com> X-Enigmail-Version: 0.95.7 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-ID: EwwjnrZ-YhxKuegdN3-mTAAuml0IFJlZgmeQnOG83yRRsNLJfbKBdbgfJraqhVzg4g X-TOI-MSGID: 13f5056e-24b8-43bf-99ec-cfceb2393870 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1376 Lines: 30 David Howells wrote: > Mike Frysinger 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 -- This footer brought to you by insane German lawmakers. Analog Devices GmbH Wilhelm-Wagenfeld-Str. 6 80807 Muenchen Sitz der Gesellschaft Muenchen, Registergericht Muenchen HRB 40368 Geschaeftsfuehrer Thomas Wessel, William A. Martin, Margaret Seif -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/