From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [Qemu-devel] Re: [PATCH 2 of 5] add can_dma/post_dma for direct IO Date: Mon, 22 Dec 2008 21:46:00 +0200 Message-ID: <494FEE78.6020006@redhat.com> References: <4942B841.6010900@codemonkey.ws> <20081213143944.GD30537@random.random> <4943E6F9.1050001@codemonkey.ws> <20081213165306.GE30537@random.random> <4944251D.8080109@codemonkey.ws> <20081214164751.GF30537@random.random> <49453BF2.9070304@redhat.com> <20081214171558.GH30537@random.random> <494565A1.6030306@redhat.com> <18767.50158.909778.205969@mariner.uk.xensource.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Andrea Arcangeli , chrisw@redhat.com, Gerd Hoffmann , kvm@vger.kernel.org To: qemu-devel@nongnu.org Return-path: Received: from mx2.redhat.com ([66.187.237.31]:53843 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752130AbYLVTqQ (ORCPT ); Mon, 22 Dec 2008 14:46:16 -0500 In-Reply-To: <18767.50158.909778.205969@mariner.uk.xensource.com> Sender: kvm-owner@vger.kernel.org List-ID: Ian Jackson wrote: > Avi Kivity writes ("[Qemu-devel] Re: [PATCH 2 of 5] add can_dma/post_dma for direct IO"): > >> Newer Xen shouldn't have this problem though; it runs qemu in kernel >> mode in a dedicated 64-bit domain. >> > > I think there is continued value in being able to emulate a guest > whose physical address space exceeds the virtual address space in the > host. The whole assumption that all guest accessible RAM is mapped at > once, contiguously, is I think wrong. > I agree that we shouldn't expect memory to be contiguous, in order to properly support hotplug. But I see zero value in trying to support large memory configurations on 32-bit in 2008. This is what 64-bit systems are for! If Xen has a problem with 64-bit hosts, we can try to accommodate it, but to have 32-bit qemu/tcg or qemu/kvm support large address spaces is pointless IMO. -- Do not meddle in the internals of kernels, for they are subtle and quick to panic.