From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: paravirtualization structure Date: Tue, 20 Feb 2007 09:14:21 +0200 Message-ID: <45DA9FCD.60009@qumranet.com> References: <45D9C127.9050201@qumranet.com> <64F9B87B6B770947A9F8391472E032160A8186EE@ehost011-8.exch011.intermedia.net> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org To: Omar Khan Return-path: In-Reply-To: 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 Omar Khan wrote: > Dor Laor writes: > > > >> Theoretically speaking the answer is yes, vmcall is a special >> instruction that it one and only purpose is the exit from the guest. >> While mov cr3 instruction might be bound to other actions of the >> processor and might have more effects on the pipeline, this harder to >> optimize for vmexit purposes. >> >> > > I guess what is confusing me is that the vmcall causes an vmexit in VMX non-root > mode (the one in which a paravirtualized guest is operating), but Avi says that > a hypercal (made using a vmcall) 'avoids' a vmentry/vmexit and Ingo comments in > his patch that : > > "This utilizes the cr3 filter capability of the hardware - if this works out > then no VM exit happens" > > NO VM-exits happen. hmmmm... maybe I need to go over the intel manuals more > thoroughly, however any hints will be most welcomed. > Using the cr3 filter does not involve a hypercall. Instead, it allows the guest to context switch without trapping on the mov %cr3 instruction, by providing a set of pre-prepared cr3s. -- Do not meddle in the internals of kernels, for they are subtle and quick to panic. ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys-and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV