Hi Alex, On Mon, 13 Dec 2021 11:40:41 +0000, Alex Bennée <alex.bennee@xxxxxxxxxx> wrote: > > Hi GIC experts, > > This came up last week in the Stratos sync call when we were discussing > Vincent's SCMI setup: > > https://linaro.atlassian.net/wiki/spaces/STR/pages/28665741503/2021-12-09+Project+Stratos+Meeting+Notes > > with the shared memory between the two guests the only reason we > currently exit to the guest userspace (QEMU) is to forward notifications > of virtqueue kicks from one guest to the other. I'm vaguely aware from > my time looking at GIC code that it can be configured for IPI IRQs > between two cores. Do we have that ability between two vCPUs from > different guests? > > If not what would it take to enable such a feature? SGIs (the interrupt type used to implement IPIs) are by definition local to a system (be it physical or virtual), and the idea of being able to route these outside the system doesn't hold. So as far as KVM is concerned, this is a strong *never*. The per-CPU nature of these interrupts is also pretty bad. It means that the guest cannot suspend some CPUs without also losing access to the device/shared memory. Bad. If you want to generate a signal that is used between VMs, why not use a global interrupt (SPI), where each VM treats the other one as a device rather than a peer? At least the semantics are manageable, and all you need to implement is some irqfd plumbing in both direction, much along the lines of what vfio (and probably vhost) already does for the exact same purpose (signalling in-kernel events to a VM). M. -- Without deviation from the norm, progress is not possible. _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
