Michael S. Tsirkin <mst@xxxxxxxxxx> writes: > On Mon, Jul 27, 2020 at 11:30:24AM +0100, Alex Bennée wrote: >> >> Stefan Hajnoczi <stefanha@xxxxxxxxxx> writes: >> >> > On Tue, Jul 21, 2020 at 11:49:04AM +0100, Alex Bennée wrote: >> >> Stefan Hajnoczi <stefanha@xxxxxxxxx> writes: <snip> >> >> 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 enabling >> >> virtio for Type-1 hypervisors like Xen and the various safety certified >> >> proprietary ones. It is unlikely that QEMU would be used as the VMM for >> >> 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. >> >> 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. >> >> > I'm sure there is room for improvement, but it seems like an incremental >> > step given that vhost-user already tries to cater for this scenario. >> > >> > Are there any specific gaps you have identified? >> >> 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. >> >> > >> > Stefan >> >> >> -- >> Alex Bennée -- Alex Bennée
