From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759037AbZEKSEQ (ORCPT ); Mon, 11 May 2009 14:04:16 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752250AbZEKSD5 (ORCPT ); Mon, 11 May 2009 14:03:57 -0400 Received: from mx2.redhat.com ([66.187.237.31]:35527 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754220AbZEKSD4 (ORCPT ); Mon, 11 May 2009 14:03:56 -0400 Message-ID: <4A086835.5020400@redhat.com> Date: Mon, 11 May 2009 21:02:29 +0300 From: Avi Kivity User-Agent: Thunderbird 2.0.0.21 (X11/20090320) MIME-Version: 1.0 To: Anthony Liguori CC: Hollis Blanchard , Gregory Haskins , Gregory Haskins , Chris Wright , linux-kernel@vger.kernel.org, kvm@vger.kernel.org Subject: Re: [RFC PATCH 0/3] generic hypercall support References: <20090505132005.19891.78436.stgit@dev.haskins.net> <4A0040C0.1080102@redhat.com> <4A0041BA.6060106@novell.com> <4A004676.4050604@redhat.com> <4A0049CD.3080003@gmail.com> <20090505231718.GT3036@sequoia.sous-sol.org> <4A010927.6020207@novell.com> <20090506072212.GV3036@sequoia.sous-sol.org> <4A018DF2.6010301@novell.com> <4A02D40D.7060307@redhat.com> <4A0448DF.90705@codemonkey.ws> <4A0570B1.30401@novell.com> <4A071F1A.1090702@codemonkey.ws> <4A0824C2.4000109@gmail.com> <1242059712.29194.12.camel@slate.austin.ibm.com> <4A085B06.4080803@redhat.com> <4A086590.4040602@codemonkey.ws> In-Reply-To: <4A086590.4040602@codemonkey.ws> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Anthony Liguori wrote: >> >> It's a question of cost vs. benefit. It's clear the benefit is low >> (but that doesn't mean it's not worth having). The cost initially >> appeared to be very low, until the nested virtualization wrench was >> thrown into the works. Not that nested virtualization is a reality >> -- even on svm where it is implemented it is not yet production >> quality and is disabled by default. >> >> Now nested virtualization is beginning to look interesting, with >> Windows 7's XP mode requiring virtualization extensions. Desktop >> virtualization is also something likely to use device assignment >> (though you probably won't assign a virtio device to the XP instance >> inside Windows 7). >> >> Maybe we should revisit the mmio hypercall idea again, it might be >> workable if we find a way to let the guest know if it should use the >> hypercall or not for a given memory range. >> >> mmio hypercall is nice because >> - it falls back nicely to pure mmio >> - it optimizes an existing slow path, not just new device models >> - it has preexisting semantics, so we have less ABI to screw up >> - for nested virtualization + device assignment, we can drop it and >> get a nice speed win (or rather, less speed loss) > > If it's a PCI device, then we can also have an interrupt which we > currently lack with vmcall-based hypercalls. This would give us > guestcalls, upcalls, or whatever we've previously decided to call them. Sorry, I totally failed to understand this. Please explain. -- Do not meddle in the internals of kernels, for they are subtle and quick to panic.