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Tsirkin" To: Jason Gunthorpe Subject: Re: [PATCH vfio 11/11] vfio/virtio: Introduce a vfio driver over virtio devices Message-ID: <20230925143708-mutt-send-email-mst@kernel.org> References: <20230921101509-mutt-send-email-mst@kernel.org> <20230921164139.GP13733@nvidia.com> <20230921124331-mutt-send-email-mst@kernel.org> <20230921183926.GV13733@nvidia.com> <20230921150448-mutt-send-email-mst@kernel.org> <20230921194946.GX13733@nvidia.com> <20230922121132.GK13733@nvidia.com> <20230925122607.GW13733@nvidia.com> MIME-Version: 1.0 In-Reply-To: <20230925122607.GW13733@nvidia.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Disposition: inline Cc: kvm@vger.kernel.org, maorg@nvidia.com, virtualization@lists.linux-foundation.org, jiri@nvidia.com, leonro@nvidia.com X-BeenThere: virtualization@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Linux virtualization List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: virtualization-bounces@lists.linux-foundation.org Sender: "Virtualization" On Mon, Sep 25, 2023 at 09:26:07AM -0300, Jason Gunthorpe wrote: > > > So, as I keep saying, in this scenario the goal is no mediation in the > > > hypervisor. > > > > That's pretty fine, but I don't think trapping + relying is not > > mediation. Does it really matter what happens after trapping? > > It is not mediation in the sense that the kernel driver does not in > any way make decisions on the behavior of the device. It simply > transforms an IO operation into a device command and relays it to the > device. The device still fully controls its own behavior. > > VDPA is very different from this. You might call them both mediation, > sure, but then you need another word to describe the additional > changes VPDA is doing. Sorry about hijacking the thread a little bit, but could you call out some of the changes that are the most problematic for you? > > > It is pointless, everything you think you need to do there > > > is actually already being done in the DPU. > > > > Well, migration or even Qemu could be offloaded to DPU as well. If > > that's the direction that's pretty fine. > > That's silly, of course qemu/kvm can't run in the DPU. > > However, we can empty qemu and the hypervisor out so all it does is > run kvm and run vfio. In this model the DPU does all the OVS, storage, > "VPDA", etc. qemu is just a passive relay of the DPU PCI functions > into VM's vPCI functions. > > So, everything VDPA was doing in the environment is migrated into the > DPU. > > In this model the DPU is an extension of the hypervisor/qemu > environment and we shift code from x86 side to arm side to increase > security, save power and increase total system performance. > > Jason I think I begin to understand. On the DPU you have some virtio devices but also some non-virtio devices. So you have to use VFIO to talk to the DPU. Reusing VFIO to talk to virtio devices too, simplifies things for you. If guests will see vendor-specific devices from the DPU anyway, it will be impossible to migrate such guests away from the DPU so the cross-vendor migration capability is less important in this use-case. Is this a good summary? -- MST _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization