From owner-freebsd-virtualization@FreeBSD.ORG Fri Aug 23 21:57:12 2013 Return-Path: Delivered-To: freebsd-virtualization@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTP id 18317D0D; Fri, 23 Aug 2013 21:57:12 +0000 (UTC) (envelope-from grehan@freebsd.org) Received: from alto.onthenet.com.au (alto.OntheNet.com.au [203.13.68.12]) by mx1.freebsd.org (Postfix) with ESMTP id CD29826F2; Fri, 23 Aug 2013 21:57:11 +0000 (UTC) Received: from dommail.onthenet.com.au (dommail.OntheNet.com.au [203.13.70.57]) by alto.onthenet.com.au (Postfix) with ESMTPS id 8361B123F4; Sat, 24 Aug 2013 07:57:09 +1000 (EST) Received: from Peter-Grehans-MacBook-Pro-2.local ([64.245.0.210]) by dommail.onthenet.com.au (MOS 4.2.4-GA) with ESMTP id BOD97667 (AUTH peterg@ptree32.com.au); Sat, 24 Aug 2013 07:57:08 +1000 Message-ID: <5217DAB2.3020204@freebsd.org> Date: Fri, 23 Aug 2013 14:57:06 -0700 From: Peter Grehan User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.6; rv:17.0) Gecko/20130801 Thunderbird/17.0.8 MIME-Version: 1.0 To: Ivan Voras Subject: Re: CFT: nested page table integration with amd64/pmap References: In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: freebsd-virtualization@freebsd.org X-BeenThere: freebsd-virtualization@freebsd.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: "Discussion of various virtualization techniques FreeBSD supports." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 23 Aug 2013 21:57:12 -0000 > I always wondered about virtualization environments which have pageable > guest memory - how does the guest kernel handle situations where it > really needs non-pageable memory? Does is simply "not care" because for > it the memory access looks just like it isn't paged but is simply very, > very slow? Yes - from the guest's point of view, what it thinks is physical memory appears wired. > What about time-sensitive situations (like the originally > mentioned PCI-passthrough)? PCI passthru is a special case since the h/w requires that the target of a DMA transfer is present - there is currently no way for the IOMMU to generate the equivalent of page faults. So, for PCI passthru, all of guest memory has to be wired host memory. For time-sensitive situations, there's not a lot of options other than forcing guest memory to be wired, since there isn't visibility into the host without having o/s-specific "tools" that could communicate this information to the hypervisor. later, Peter.