From owner-freebsd-hackers@FreeBSD.ORG  Tue Jul 28 16:33:00 2009
Return-Path: <owner-freebsd-hackers@FreeBSD.ORG>
Delivered-To: freebsd-hackers@freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34])
	by hub.freebsd.org (Postfix) with ESMTP id F34D5106564A
	for <freebsd-hackers@freebsd.org>; Tue, 28 Jul 2009 16:32:59 +0000 (UTC)
	(envelope-from simon@comsys.ntu-kpi.kiev.ua)
Received: from comsys.ntu-kpi.kiev.ua (comsys.ntu-kpi.kiev.ua [77.47.192.42])
	by mx1.freebsd.org (Postfix) with ESMTP id 6C3A98FC0A
	for <freebsd-hackers@freebsd.org>; Tue, 28 Jul 2009 16:32:56 +0000 (UTC)
	(envelope-from simon@comsys.ntu-kpi.kiev.ua)
Received: from pm513-1.comsys.ntu-kpi.kiev.ua (pm513-1.comsys.ntu-kpi.kiev.ua
	[10.18.52.101]) (authenticated bits=0)
	by comsys.ntu-kpi.kiev.ua (8.13.7/8.13.7) with ESMTP id n6SFtqYD080117
	(version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO);
	Tue, 28 Jul 2009 18:55:52 +0300 (EEST)
Received: by pm513-1.comsys.ntu-kpi.kiev.ua (Postfix, from userid 1001)
	id 7092F1CC39; Tue, 28 Jul 2009 18:55:38 +0300 (EEST)
Date: Tue, 28 Jul 2009 18:55:38 +0300
From: Andrey Simonenko <simon@comsys.ntu-kpi.kiev.ua>
To: Andrew Brampton <brampton+freebsd-hackers@gmail.com>
Message-ID: <20090728155538.GA77306@pm513-1.comsys.ntu-kpi.kiev.ua>
References: <d41814900907200814w4371871cp3529a1e97239e1b9@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <d41814900907200814w4371871cp3529a1e97239e1b9@mail.gmail.com>
User-Agent: Mutt/1.5.20 (2009-06-14)
X-Virus-Scanned: ClamAV version 0.93.1,
	clamav-milter version 0.93.1 on comsys.ntu-kpi.kiev.ua
X-Virus-Status: Clean
X-Spam-Status: No, score=-4.4 required=5.0 tests=ALL_TRUSTED,BAYES_00 
	autolearn=ham version=3.1.4
X-Spam-Checker-Version: SpamAssassin 3.1.4 (2006-07-25) on 
	comsys.ntu-kpi.kiev.ua
Cc: freebsd-hackers@freebsd.org
Subject: Re: vm_map_protect / pmap_protect Can't lower protection
X-BeenThere: freebsd-hackers@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: Technical Discussions relating to FreeBSD
	<freebsd-hackers.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-hackers>, 
	<mailto:freebsd-hackers-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-hackers>
List-Post: <mailto:freebsd-hackers@freebsd.org>
List-Help: <mailto:freebsd-hackers-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-hackers>,
	<mailto:freebsd-hackers-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Tue, 28 Jul 2009 16:33:00 -0000

Hello Andrew,

On Mon, Jul 20, 2009 at 04:14:02PM +0100, Andrew Brampton wrote:

> However, memguard_unguard doesn't work correctly. It first calls
> vm_map_protect with a read-write flag.
> vm_map_protect correctly updates the vm_map_entry, and then calls
> pmap_protect to set the actual pte.
> pmap_protect is lazy and notices that we are reducing the protection
> on the page and therefore does nothing. It assumes that later that a
> page fault will occur, call vm_fault, and then fix up the pte then.

As I remember, pmap_protect() is used for removing permissions, it
cannot be used (even in initial versions of pmap code) for lowering
permissions.  pmap_enter() can be used to lower permissions, this
is even written in its comments.