From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from bombadil.infradead.org (bombadil.infradead.org [IPv6:2607:7c80:54:e::133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 41l4Cl29RPzDqMh for ; Tue, 7 Aug 2018 16:21:23 +1000 (AEST) Date: Mon, 6 Aug 2018 23:21:17 -0700 From: Christoph Hellwig To: Benjamin Herrenschmidt Cc: Christoph Hellwig , "Michael S. Tsirkin" , Will Deacon , Anshuman Khandual , virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, aik@ozlabs.ru, robh@kernel.org, joe@perches.com, elfring@users.sourceforge.net, david@gibson.dropbear.id.au, jasowang@redhat.com, mpe@ellerman.id.au, linuxram@us.ibm.com, haren@linux.vnet.ibm.com, paulus@samba.org, srikar@linux.vnet.ibm.com, robin.murphy@arm.com, jean-philippe.brucker@arm.com, marc.zyngier@arm.com Subject: Re: [RFC 0/4] Virtio uses DMA API for all devices Message-ID: <20180807062117.GD32709@infradead.org> References: <20180803070507.GA1344@infradead.org> <20180803160246.GA13794@infradead.org> <22310f58605169fe9de83abf78b59f593ff7fbb7.camel@kernel.crashing.org> <20180804082120.GB4421@infradead.org> <20180805072930.GB23288@infradead.org> <20180806094243.GA16032@infradead.org> <6c707d6d33ac25a42265c2e9b521c2416d72c739.camel@kernel.crashing.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <6c707d6d33ac25a42265c2e9b521c2416d72c739.camel@kernel.crashing.org> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Tue, Aug 07, 2018 at 05:52:12AM +1000, Benjamin Herrenschmidt wrote: > > It is your job to write a coherent interface specification that does > > not depend on the used components. The hypervisor might be PAPR, > > Linux + qemu, VMware, Hyperv or something so secret that you'd have > > to shoot me if you had to tell me. The guest might be Linux, FreeBSD, > > AIX, OS400 or a Hipster project of the day in Rust. As long as we > > properly specify the interface it simplify does not matter. > > That's the point Christoph. The interface is today's interface. It does > NOT change. That information is not part of the interface. > > It's the VM itself that is stashing away its memory in a secret place, > and thus needs to do bounce buffering. There is no change to the virtio > interface per-se. Any guest that doesn't know about your magic limited adressing is simply not going to work, so we need to communicate that fact.