From owner-freebsd-arch@FreeBSD.ORG Fri Sep 15 20:44:43 2006 Return-Path: X-Original-To: freebsd-arch@freebsd.org Delivered-To: freebsd-arch@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 3AC8716A407 for ; Fri, 15 Sep 2006 20:44:43 +0000 (UTC) (envelope-from jhb@freebsd.org) Received: from server.baldwin.cx (66-23-211-162.clients.speedfactory.net [66.23.211.162]) by mx1.FreeBSD.org (Postfix) with ESMTP id 843BF43D46 for ; Fri, 15 Sep 2006 20:44:42 +0000 (GMT) (envelope-from jhb@freebsd.org) Received: from localhost.corp.yahoo.com (john@localhost [127.0.0.1]) (authenticated bits=0) by server.baldwin.cx (8.13.6/8.13.6) with ESMTP id k8FKiNst053364; Fri, 15 Sep 2006 16:44:24 -0400 (EDT) (envelope-from jhb@freebsd.org) From: John Baldwin To: LI Xin Date: Fri, 15 Sep 2006 16:44:26 -0400 User-Agent: KMail/1.9.1 References: <450AB80B.1050100@delphij.net> <200609151251.16371.jhb@freebsd.org> <450AE7FE.5000905@delphij.net> In-Reply-To: <450AE7FE.5000905@delphij.net> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200609151644.27040.jhb@freebsd.org> X-Greylist: Sender succeeded SMTP AUTH authentication, not delayed by milter-greylist-2.0.2 (server.baldwin.cx [127.0.0.1]); Fri, 15 Sep 2006 16:44:24 -0400 (EDT) X-Virus-Scanned: ClamAV 0.88.3/1885/Fri Sep 15 07:19:10 2006 on server.baldwin.cx X-Virus-Status: Clean X-Spam-Status: No, score=-4.4 required=4.2 tests=ALL_TRUSTED,AWL,BAYES_00 autolearn=ham version=3.1.3 X-Spam-Checker-Version: SpamAssassin 3.1.3 (2006-06-01) on server.baldwin.cx Cc: freebsd-arch@freebsd.org Subject: Re: How to map a page with userland program? X-BeenThere: freebsd-arch@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussion related to FreeBSD architecture List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 15 Sep 2006 20:44:43 -0000 On Friday 15 September 2006 13:50, LI Xin wrote: > John Baldwin wrote: > > On Friday 15 September 2006 11:21, LI Xin wrote: > >> John Baldwin wrote: > >>> On Friday 15 September 2006 10:26, LI Xin wrote: > >>>> Dear folks, > >>>> > >>>> Is there a continent and MI way to map a kernel page into userland > >>>> address space under the same virtual address? It seems that this can be > >>>> implemented through some routines in MD part of pmap, but is it possible > >>>> to use higher level VM routines to do the job? > >>> Not to the same userland virtual address. Why do you need the same > >>> virtual address anyway? If it's for pointers use offsets relative to > >>> the start of the page instead. > >> That would make it easier to implement some sort of VSYSCALL, which is > >> in fact executed in userland. Or, is there any better way? :-) > > > > If you want to stick code in the page, make the code PIC, the same as is done > > for shared libraries. Alternatively, if you wanted to be very, very evil and > > can have the page read-only once it is initialized, flip the user/supervisor > > bit in the kernel PTE for that page such that it is treated as a user page > > rather than a kernel page (even though it's in KVA), and then userland > > processes can access that page via it's kernel VA. Making the code PIC would > > probably be better though. > > I see... So, what if I want to make some data available to userland? > Is flipping the user/supervisor bit the only way? Well, it's a quicker hack than the much more complicated way. Otherwise, you have to make sure everyone agrees on the same address. Hmm, I suppose actually you could just use a simple dummy device driver that creates a /dev/foo and mmap it using MMAP_FIXED with your chosen userland virtual address. Then in your driver you just need to malloc a page and use vtophys() to get a phys_addr to hand back in your d_mmap() routine. -- John Baldwin