On Tue, 2023-01-17 at 10:56 +0000, Paul Durrant wrote:
>
> I'm just having a hard time seeing why passing 0 to
> xen_evtchn_set_callback_param() does anything useful...
>
> + switch (param >> CALLBACK_VIA_TYPE_SHIFT) {
> + case HVM_PARAM_CALLBACK_TYPE_VECTOR: {
> + struct kvm_xen_hvm_attr xa = {
> + .type = KVM_XEN_ATTR_TYPE_UPCALL_VECTOR,
> + .u.vector = (uint8_t)param,
> + };
>
> HVM_PARAM_CALLBACK_TYPE_VECTOR is 2 AFAICT, so it won't hit that case.
> Also, you appear to be passing the unshifted param to kernel anyway.
>
> What is the call trying to achieve?Zero is HVM_PARAM_CALLBACK_TYPE_GSI, with GSI==0. It's basically disabling event channel delivery for the new kernel.
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