From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeremy Fitzhardinge Subject: Re: PV guest + shadow paging Date: Wed, 24 Oct 2007 11:59:07 -0700 Message-ID: <471F95FB.8000309@goop.org> References: Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Keir Fraser Cc: Tim Deegan , Ian Pratt , xen-devel@lists.xensource.com, Levin Johnson , Ian Campbell List-Id: xen-devel@lists.xenproject.org Keir Fraser wrote: > On 24/10/07 11:00, "Jeremy Fitzhardinge" wrote: > > >> Tim Deegan wrote: >> >>> The joy of NPT(VMI?)/EPT is that you don't need shadow pagetables at >>> all. :) >>> >>> >> Sure, but from a guest interface perspective they look the same. >> > > Would you want to take advantage of NPT/EPT once you've pv'ed your mmu > interfaces? > I think so. NPT/EPT would seem to have all the advantages of shadow paging and direct paging without the disadvantages. We would avoid taking faults/hypercalls on pagetable updates, and have the secondary benefit of not needing to worry about page permissions on pagetables, making it easier to use superpages for the kernel and in general. Perhaps the initial implementations will be sufficiently poor that it isn't worth doing now, but I think it will in time. J