From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: KVM & VMX root mode Date: Mon, 03 Sep 2007 14:34:19 +0300 Message-ID: <46DBF13B.9080005@qumranet.com> References: <46D81156.8050100@innotek.de> <46D97669.7050609@qumranet.com> <46D980C2.3040501@innotek.de> <46D98C53.4070604@qumranet.com> <46D9A030.1020904@innotek.de> <46D9B297.5070502@qumranet.com> <20070903031403.GA16190@redhat.com> <46DBB7C1.60708@innotek.de> <46DBBB65.3020406@qumranet.com> <46DBC120.3050301@innotek.de> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org To: Sander van Leeuwen Return-path: In-Reply-To: <46DBC120.3050301-2taLTamkYL2ELgA04lAiVw@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Errors-To: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: kvm.vger.kernel.org Sander van Leeuwen wrote: > Avi Kivity wrote: >> Sander van Leeuwen wrote: >> >>> You are mistaken. VT-x allows multiple clients to work concurrently. >>> There's only one catch: all those >>> clients should follow certain guidelines. >>> >> >> Currently, kvm assumes that it is the only user that issues vmptrld >> instructions. There may me other such assumptions in the code. >> >> There is also the question of who issues the vmxon/vmxoff instructions >> and set the magic msr bits that enable kvm. You can't have two >> hypervisors doing that; that would be racy. It should be possible to >> abstract those bits out to something outside kvm, but I don't see that >> happening. >> >> > VirtualBox currently always executes vmxon when it wants to execute > some guest code. When leaving > ring 0 it issues the corresponding vmxoff. While that may increase > world switch overhead, it has not turned > out to be an issue for us. The overhead will increase with newer hardware, as more state is cached on-chip. It's probably okay when deploying to a desktop but i don't think it is good enough for a server. > I think it's a bit risky to use somebody else's vmxon pointer. > > You have a point with the msr updates though. I think the easiest way forward is for you to unload kvm-intel (or kvm-amd) when you load, and to reload it when you unload. -- error compiling committee.c: too many arguments to function ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/