Re: [PATCH v7 26/51] hw/xen: Add xen_evtchn device for event channel emulation

[David Woodhouse]

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.

smime.p7s
Description: S/MIME cryptographic signature