From owner-freebsd-ppc@FreeBSD.ORG Tue Apr 15 16:51:29 2008 Return-Path: Delivered-To: freebsd-ppc@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id E5D1A1065671 for ; Tue, 15 Apr 2008 16:51:29 +0000 (UTC) (envelope-from grehan@freebsd.org) Received: from alto.onthenet.com.au (alto.OntheNet.com.au [203.13.68.12]) by mx1.freebsd.org (Postfix) with ESMTP id A1D0C8FC22 for ; Tue, 15 Apr 2008 16:51:29 +0000 (UTC) (envelope-from grehan@freebsd.org) Received: from dommail.onthenet.com.au (dommail.OntheNet.com.au [203.13.70.57]) by alto.onthenet.com.au (Postfix) with ESMTP id 46001120E1; Wed, 16 Apr 2008 02:51:25 +1000 (EST) Received: from peter-grehans-power-mac-g5.local (dsl-63-249-90-35.cruzio.com [63.249.90.35]) by dommail.onthenet.com.au (MOS 3.7.5a-GA) with ESMTP id DVX13406 (AUTH peterg@ptree32.com.au); Wed, 16 Apr 2008 02:51:25 +1000 (EST) Message-ID: <4804DD02.10304@freebsd.org> Date: Tue, 15 Apr 2008 09:51:14 -0700 From: Peter Grehan User-Agent: Thunderbird 2.0.0.12 (Macintosh/20080213) MIME-Version: 1.0 To: Marcel Moolenaar References: <4804AE13.2060600@uchicago.edu> <4804C9E9.6010303@freebsd.org> <5CC81F06-7B59-4163-9AB8-2ACE4235A5AA@mac.com> In-Reply-To: <5CC81F06-7B59-4163-9AB8-2ACE4235A5AA@mac.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: freebsd-ppc@freebsd.org Subject: Re: G5 Bridge-mode MMU X-BeenThere: freebsd-ppc@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list Reply-To: grehan@freebsd.org List-Id: Porting FreeBSD to the PowerPC List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 15 Apr 2008 16:51:30 -0000 Hi Marcel, > There's a bigger problem though: the current AIM pmap code and > exception handling is broken for kernel stacks. I've not seen any evidence of this. Granted, I've only tested with psim, but I can safely access all of kstack0's virtual address space. All of the stack pages are wired, as are the mappings. Where are the DSI exceptions occurring ? Stack *overflow* exception handling may be busted, but that is a challenging problem to get right. > Also, with process address space limited to 2G Where's that limitation ? If so, that's a bug: it should be 4G. > I wonder why we > keep swapping all segment registers and not just the lower 8? As above. That was taken from NetBSD to give the full 4G address space for users. It used to be the high 8 seg regs, since the lower 2G was either 1:1 BAT-mapped memory or PCI mem space. > Related: how hard would it be to map the kernel above 2G and > eliminate the SR swap in the exception handlers (but do it on > context switches)? You would have to eliminate the 1:1 mapping. I know this was done in the bookE port, and it is painful to have two kernel ABIs. How about the corollary: how hard is it to get the bookE port to use a separate address space for the kernel ? later, Peter.