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Tsirkin" Subject: Re: Inter-VM device emulation (call on Mon 20th July 2020) In-reply-to: <20200727073311-mutt-send-email-mst@kernel.org> Date: Mon, 27 Jul 2020 13:22:29 +0100 Message-ID: <87eeox406y.fsf@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=2a00:1450:4864:20::432; envelope-from=alex.bennee@linaro.org; helo=mail-wr1-x432.google.com X-detected-operating-system: by eggs.gnu.org: No matching host in p0f cache. That's all we know. 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, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, 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: "John G. Johnson" , Jag Raman , Andra-Irina Paraschiv , kvm , Jean-Philippe Brucker , Stefan Hajnoczi , qemu-devel , Eric Auger , Maxime Coquelin , Alexander Graf , Stefan Hajnoczi , Jan Kiszka , Thanos Makatos , Nikos Dragazis , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Michael S. Tsirkin writes: > On Mon, Jul 27, 2020 at 11:30:24AM +0100, Alex Benn=C3=83=C2=A9e wrote: >>=20 >> Stefan Hajnoczi writes: >>=20 >> > On Tue, Jul 21, 2020 at 11:49:04AM +0100, Alex Benn=C3=83=C2=A9e wrote: >> >> Stefan Hajnoczi writes: >> >> Another thing that came across in the call was quite a lot of >> >> assumptions about QEMU and Linux w.r.t virtio. While our project will >> >> likely have Linux as a guest OS we are looking specifically at enabli= ng >> >> virtio for Type-1 hypervisors like Xen and the various safety certifi= ed >> >> proprietary ones. It is unlikely that QEMU would be used as the VMM f= or >> >> these deployments. We want to work out what sort of common facilities >> >> hypervisors need to support to enable virtio so the daemons can be >> >> re-usable and maybe setup with a minimal shim for the particular >> >> hypervisor in question. >> > >> > The vhost-user protocol together with the backend program conventions >> > define the wire protocol and command-line interface (see >> > docs/interop/vhost-user.rst). >> > >> > vhost-user is already used by other VMMs today. For example, >> > cloud-hypervisor implements vhost-user. >>=20 >> Ohh that's a new one for me. I see it is a KVM only project but it's >> nice to see another VMM using the common rust-vmm backend. There is >> interest in using rust-vmm to implement VMMs for type-1 hypervisors but >> we need to work out if there are two many type-2 concepts backed into >> the lower level rust crates. >>=20 >> > I'm sure there is room for improvement, but it seems like an increment= al >> > step given that vhost-user already tries to cater for this scenario. >> > >> > Are there any specific gaps you have identified? >>=20 >> Aside from the desire to limit the shared memory footprint between the >> backend daemon and a guest not yet. > > So it's certainly nice for security but not really a requirement for a > type-1 HV, right? Not a requirement per-se but type-1 setups don't assume a "one userspace to rule them all" approach. >> I suspect the eventfd mechanism might just end up being simulated by the >> VMM as a result of whatever comes from the type-1 interface indicating a >> doorbell has been rung. It is after all just a FD you consume numbers >> over right? > > Does not even have to be numbers. We need a way to be woken up, a way to > stop/start listening for wakeups and a way to detect that there was a > wakeup while we were not listening. > > Though there are special tricks for offloads where we poke through > layers in order to map things directly to hardware. > >> Not all setups will have an equivalent of a Dom0 "master" guest to do >> orchestration. Highly embedded are likely to have fixed domains created >> as the firmware/hypervisor start up. >>=20 >> > >> > Stefan >>=20 >>=20 >> --=20 >> Alex Benn=C3=83=C2=A9e --=20 Alex Benn=C3=A9e