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[79.182.97.190]) by smtp.gmail.com with ESMTPSA id y2sm21976969wrh.0.2020.11.02.02.35.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 02 Nov 2020 02:35:05 -0800 (PST) Date: Mon, 2 Nov 2020 05:34:50 -0500 From: "Michael S. Tsirkin" To: Stefan Hajnoczi Subject: Re: Out-of-Process Device Emulation session at KVM Forum 2020 Message-ID: <20201102053142-mutt-send-email-mst@kernel.org> References: <20201029083130.0617a28f@w520.home> <20201029094603.15382476@w520.home> <20201029210407.33d6f008@x1.home> <04179584-3324-994e-d793-04be18d2dab2@redhat.com> <0cabda60-f10d-fb74-f3eb-d21be7db7334@redhat.com> <20201102102754.GB42093@stefanha-x1.localdomain> MIME-Version: 1.0 In-Reply-To: <20201102102754.GB42093@stefanha-x1.localdomain> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mst@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=mst@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/11/02 01:33:03 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Elena Ufimtseva , John G Johnson , Janosch Frank , Stefan Hajnoczi , Jason Wang , qemu-devel , Kirti Wankhede , Gerd Hoffmann , Yan Vugenfirer , Jag Raman , Christian Borntraeger , Anup Patel , Claudio Imbrenda , Eugenio =?iso-8859-1?Q?P=E9rez?= , Roman Kagan , Felipe Franciosi , =?iso-8859-1?Q?Marc-Andr=E9?= Lureau , Jens Freimann , Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= , Stefano Garzarella , Eduardo Habkost , Sergio Lopez , Kashyap Chamarthy , Darren Kenny , Alex Williamson , Liran Alon , Paolo Bonzini , Alex =?iso-8859-1?Q?Benn=E9e?= , David Gibson , Kevin Wolf , Halil Pasic , "Daniel P. Berrange" , Christophe de Dinechin , Thanos Makatos , fam Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, Nov 02, 2020 at 10:27:54AM +0000, Stefan Hajnoczi wrote: > On Mon, Nov 02, 2020 at 11:00:12AM +0800, Jason Wang wrote: > > > > On 2020/10/30 下午7:13, Stefan Hajnoczi wrote: > > > > I still don't get why it must be opaque. > > > If the device state format needs to be in the VMM then each device > > > needs explicit enablement in each VMM (QEMU, cloud-hypervisor, etc). > > > > > > Let's invert the question: why does the VMM need to understand the > > > device state of a_passthrough_ device? > > > > > > It's not a 100% passthrough device if you want to support live migration. > > E.g the device state save and restore is not under the control of drivers in > > the guest. > > VFIO devices are already not pure passthrough (even without mdev) since > the PCI bus is emulated and device-specific quirks may be implemented. So since it's not a pure passthrough anyway, let's try to introduce some standards even if we can not always enforce them. > Adding device state save/load does not change anything here. It's as good a time as any to try to standardize things and not just let each driver do whatever it wants. In particular if you consider things like cross version support it's a hard problem where vendors are sure to get it wrong without guidance. -- MST