Avi Kivity wrote: > Gregory Haskins wrote: >>> Don't - it's broken. It will also catch device assignment mmio and >>> hypercall them. >>> >>> >> Ah. Crap. >> >> Would you be conducive if I continue along with the dynhc() approach >> then? >> > > Oh yes. But don't call it dynhc - like Chris says it's the wrong > semantic. > > Since we want to connect it to an eventfd, call it HC_NOTIFY or > HC_EVENT or something along these lines. You won't be able to pass > any data, but that's fine. Registers are saved to memory anyway. Ok, but how would you access the registers since you would presumably only be getting a waitq::func callback on the eventfd. Or were you saying that more data, if required, is saved in a side-band memory location? I can see the latter working. I can't wrap my head around the former. > > And btw, given that eventfd and the underlying infrastructure are so > flexible, it's probably better to go back to your original "irqfd gets > fd from userspace" just to be consistent everywhere. > > (no, I'm not deliberately making you rewrite that patch again and > again... it's going to be a key piece of infrastructure so I want to > get it right) Ok, np. Actually now that Davide showed me the waitq::func trick, the fd technically doesn't even need to be an eventfd per se. We can just plain-old "fget()" it and attach via the f_ops->poll() as I do in v5. Ill submit this later today. > > > Just to make sure we have everything plumbed down, here's how I see > things working out (using qemu and virtio, use sed to taste): > > 1. qemu starts up, sets up the VM > 2. qemu creates virtio-net-server > 3. qemu allocates six eventfds: irq, stopirq, notify (one set for tx > ring, one set for rx ring) > 4. qemu connects the six eventfd to the data-available, > data-not-available, and kick ports of virtio-net-server > 5. the guest starts up and configures virtio-net in pci pin mode > 6. qemu notices and decides it will manage interrupts in user space > since this is complicated (shared level triggered interrupts) > 7. the guest OS boots, loads device driver > 8. device driver switches virtio-net to msix mode > 9. qemu notices, plumbs the irq fds as msix interrupts, plumbs the > notify fds as notifyfd > 10. look ma, no hands. > > Under the hood, the following takes place. > > kvm wires the irqfds to schedule a work item which fires the > interrupt. One day the kvm developers get their act together and > change it to inject the interrupt directly when the irqfd is signalled > (which could be from the net softirq or somewhere similarly nasty). > > virtio-net-server wires notifyfd according to its liking. It may > schedule a thread, or it may execute directly. > > And they all lived happily ever after. Ack. I hope when its all said and done I can convince you that the framework to code up those virtio backends in the kernel is vbus ;) But even if not, this should provide enough plumbing that we can all coexist together peacefully. Thanks, -Greg
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