Re: [Qemu-devel] [PATCH v3 1/2] s390x/pci: Introduce unplug requests and split unplug handler

[Pierre Morel]

On 29/01/2019 16:14, David Hildenbrand wrote:
> On 29.01.19 14:31, Pierre Morel wrote:
> > On 21/01/2019 14:42, David Hildenbrand wrote:
> > > PCI on s390x is really weird and how it was modeled in QEMU might not have
> > > been the right choice. Anyhow, right now it is the case that:
> > > - Hotplugging a PCI device will silently create a zPCI device
> > >     (if none is provided)
> > > - Hotunplugging a zPCI device will unplug the PCI device (if any)
> > > - Hotunplugging a PCI device will unplug also the zPCI device
> > > As far as I can see, we can no longer change this behavior. But we
> > > should fix it.


> > So unplugging PCI first will deny the guest any possibility to smoothly
> > relinquish a device.
> >
> >
> > Is it possible the other way around?
>
> Maybe, but it does not really matter. We unplug both devices
> synchronously, without the guest recognizing the order. We always have
> the unplug request first that notifies the guest. When we get an ACK
> from the guest, we can unpplug both devices in any order.
>
> (and if we want to change the order, we should do it in a separate
> patch, this patch does not change the order, just refactors the code)


If it is done atomically, then I have no objection.

Regards,
Pierre



--
Pierre Morel
Linux/KVM/QEMU in Böblingen - Germany