Re: [Xen-devel] [PATCH 23/25] argo: signal x86 HVM and ARM via VIRQ

[Christopher Clark <christopher.w.clark@xxxxxxxxx>]

On Thu, Dec 13, 2018 at 6:16 AM Jan Beulich <JBeulich@xxxxxxxx> wrote:
>
> >>> On 01.12.18 at 02:33, <christopher.w.clark@xxxxxxxxx> wrote:
> > * x86 PV domains are notified via event channel.
> >
> > PV guests are known to have the event channel software present in the guest
> > kernel, so it is fine to depend on and use it.
> >
> > * x86 HVM domains and all ARM domains are notified via VIRQ.
> >
> > The intent is to remove the requirement for event channel software to be
> > installed within these guests in order to use Argo. VIRQ signalling is also
> > the method that has been in use for the longest period with this hypercall
> > in both XenClient and OpenXT.
>
> I'm afraid I don't follow: send_guest_global_virq() uses, well,
> evtchn_port_set_pending(), just like evtchn_send() does.
> Therefore how does sending a vIRQ help with a guest without
> event channel awareness?

On this topic, signal delivery to guests, I'm simplifying the next version of
the patch series: I'm just going to use VIRQs.

It doesn't remove the dependency on event channel software in the guest,
and it doesn't optimize efficiency of notifications with HVM guests
but I'd like to come back and address that in a subsequent patch once
this series has been accepted. It'll follow from the explanation
that James's message provides.

Christopher

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