| Subject | Re: [PATCH RFC 11/39] KVM: x86/xen: evtchn signaling via eventfd | From | David Woodhouse <> | Date | Mon, 30 Nov 2020 09:41:16 +0000 |
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On Wed, 2019-02-20 at 20:15 +0000, Joao Martins wrote: > userspace registers a @port to an @eventfd, that is bound to a > @vcpu. This information is then used when the guest does an > EVTCHNOP_send with a port registered with the kernel.
Why do I want this part?
> EVTCHNOP_send short-circuiting happens by marking the event as pending > in the shared info and vcpu info pages and doing the upcall. For IPIs > and interdomain event channels, we do the upcall on the assigned vcpu.
This part I understand, 'peeking' at the EVTCHNOP_send hypercall so that we can short-circuit IPI delivery without it having to bounce through userspace.
But why would I then want then short-circuit the short-circuit, providing an eventfd for it to signal... so that I can then just receive the event in userspace in a *different* form to the original hypercall exit I would have got?
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