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Re: [Xen-devel] [PATCH 15/22] vixen: pass through version hypercalls to parent Xen

On Sun, Jan 7, 2018 at 12:31 AM, Roger Pau Monné <roger.pau@xxxxxxxxxx> wrote:
> On Sat, Jan 06, 2018 at 02:54:30PM -0800, Anthony Liguori wrote:
>> From: Anthony Liguori <aliguori@xxxxxxxxxx>
>> This is necessary to trigger event channel upcalls but it is also
> I'm lost here, what does version have to do with upcalls?

In Linux, xen_force_evtchn_callback() does HYPERVISOR_xen_version(0,
NULL).  This is done when IRQs are re-enabled after being disabled to
trigger checking pending.

I'm not 100% confident that it's necessary to pass this all the way
through to the parent Xen but it seemed like the right thing to do
since we need the parent to update pending events in order for the
events in Vixen to get updated.

>> useful to passthrough the full version information such that the
>> guest believes it is running on the parent Xen.
> In any case, I think this is wrong. The interface the guest sees is
> the interface from vixen, not the interface of the L0. Hence reporting
> the L0 version is not appropriate.

I think it depends on what you want.  We were aiming for maximum
compatibility and many users trigger behavior from Xen version for
better or worse.

Happy to make this optional if this isn't universally desired.


Anthony Liguori

> Thanks, Roger.
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