+Stewart On Fri, 8 Dec 2023, Mykyta Poturai wrote: > Hello everyone, > > I am currently working on adding MSI support to virtio-pci on ARM with Xen.
Excellent! > As far as I understand QEMU Xen ARM machine that is used for virtio-pci > device emulation does not initialize any interrupt controllers. And that > makes it somewhat unclear what is the best approach to adding the MSI > support. So, I would appreciate some thoughts on this. > To trigger the MSI interrupt in Xen guests we basically need to call a single > DMOP, which I am also implementing. You should be able to call xen_inject_msi > So far, I have come up with 3 possible approaches: > 1. Hooking up the existing GIC code to the Xen Arm machine and extending it > with the DMOP call. No, I would rather avoid this for a couple of reasons. In reality, the GIC is emulated by Xen, not QEMU. So letting QEMU think that QEMU is emulating a GIC is more error prone than the alternatives and also it would allocate resources needlessly. > 2. Writing some new barebones GIC implementation with only the required > methods (something similar to xen_apic.c). > 3. Just hooking up the DMOP call to the existing PCI code based on > xen_enabled() check. I would rather not introduce any more if (xen_enabled()) checks beyond the ones we already have unless it is the only option. So I would go with option 2). Even better if we could reuse xen_apic.c. xen_apic.c is just a stub, which is basically the same thing that we need here.
