From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1JL0BX-0001JC-7Z for qemu-devel@nongnu.org; Fri, 01 Feb 2008 13:00:19 -0500 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1JL0BV-0001Hu-6o for qemu-devel@nongnu.org; Fri, 01 Feb 2008 13:00:18 -0500 Received: from [199.232.76.173] (helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1JL0BV-0001Hp-1W for qemu-devel@nongnu.org; Fri, 01 Feb 2008 13:00:17 -0500 Received: from mx1.redhat.com ([66.187.233.31]) by monty-python.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1JL0BU-0008LM-K3 for qemu-devel@nongnu.org; Fri, 01 Feb 2008 13:00:16 -0500 Date: Fri, 1 Feb 2008 17:57:50 +0000 From: "Daniel P. Berrange" Subject: Re: [kvm-devel] [Qemu-devel] Re: [PATCH 1/6] Use correct types to enable > 2G support Message-ID: <20080201175750.GD22981@redhat.com> References: <1201818980-27534-1-git-send-email-aliguori@us.ibm.com> <1201818980-27534-2-git-send-email-aliguori@us.ibm.com> <47A2F3C7.6060409@bellard.org> <47A32E40.3000204@us.ibm.com> <47A33721.4020600@qumranet.com> <47A33BC6.3060705@us.ibm.com> <18339.15712.411486.395238@mariner.uk.xensource.com> <47A35C7E.8050309@codemonkey.ws> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <47A35C7E.8050309@codemonkey.ws> Reply-To: "Daniel P. Berrange" , qemu-devel@nongnu.org List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Anthony Liguori Cc: kvm-devel@lists.sourceforge.net, Ian Jackson , qemu-devel@nongnu.org, Paul Brook On Fri, Feb 01, 2008 at 11:53:02AM -0600, Anthony Liguori wrote: > Ian Jackson wrote: > > Anthony Liguori writes ("[Qemu-devel] Re: [kvm-devel] [PATCH 1/6] Use correct types to enable > 2G support"): > > > >> The alternative is to change all the places that assume phys_ram_base + > >> PA which I don't like very much. > >> > > > > We would ideally like to do this for Xen, at least in the places we > > care about. (Xen uses less of the qemu tree than KVM, I think.) > > > > Support for the map cache in the Xen tree is a rather big change that > I'm not going to attempt to support it in this patch series. > > I'd rather preserve the phys_ram_base + PA assumption because it allows > us to be able to do support > 1 page DMA operations for our virtual IO > drivers. If you break the assumption that physically contiguous memory > in the guest is virtual contiguous memory in the host, things get pretty > ugly. Well Xen i386 has no choice but to use the map cache, since PAE lets i386 guests have as much as 100 GB of memory & there's no way you can map that into QEMU's 32-bit userspace. So if virt IO has a dependancy on contigious memory access in QEMU its not going to play nice with Xen. Dan. -- |=- Red Hat, Engineering, Emerging Technologies, Boston. +1 978 392 2496 -=| |=- Perl modules: http://search.cpan.org/~danberr/ -=| |=- Projects: http://freshmeat.net/~danielpb/ -=| |=- GnuPG: 7D3B9505 F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505 -=|