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Date: Wed, 23 Jan 2019 12:05:39 +0100
From: Cornelia Huck <cohuck@redhat.com>
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	<20190121134249.16615-3-david@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v3 2/2] s390x/pci: Unplug remaining devices
 on pcihost reset
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To: David Hildenbrand <david@redhat.com>
Cc: qemu-devel@nongnu.org, qemu-s390x@nongnu.org, Collin Walling <walling@linux.ibm.com>, Thomas Huth <thuth@redhat.com>, Christian Borntraeger <borntraeger@de.ibm.com>, Richard Henderson <rth@twiddle.net>

On Mon, 21 Jan 2019 14:42:49 +0100
David Hildenbrand <david@redhat.com> wrote:

> When resetting the guest we should unplug and remove all devices that
> are still pending. Otherwise the fresh guest will see devices that will
> suddenly vanish.
> 
> Can be triggered e.g. via
> (hmp) device_add virtio-mouse-pci,id=test
> (hmp) stop
> (hmp) device_del test
> (hmp) system_reset
> (hmp) c
> 
> The device will vanish after roughly 5 minutes. With this patch, the
> device will vanish on reboot (S390_RESET_EXTERNAL and S390_RESET_REIPL,
> which reset the pcihost bridge via qemu_devices_reset()). If we want
> these devices to vanish directly on any reset (S390_RESET_MODIFIED_CLEAR
> and S390_RESET_LOAD_NORMAL), we have to modify s390_machine_reset(). But
> I have the feeling that this should not be done for all reset types.
> 
> This approach is similar to what's done for acpi PCI hotplug in
> acpi_pcihp_reset() -> acpi_pcihp_update() ->
> acpi_pcihp_update_hotplug_bus() -> acpi_pcihp_eject_slot().
> 
> s390_pci_generate_plug_event()'s will still be generated, I guess this
> is not an issue (same thing could happen right now if the timer expires
> just after reset).

I'm wondering what the architecture says regarding those events -- can
someone with access to the documentation comment?

> 
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>  hw/s390x/s390-pci-bus.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/hw/s390x/s390-pci-bus.c b/hw/s390x/s390-pci-bus.c
> index bc17a8cf65..b70ae25533 100644
> --- a/hw/s390x/s390-pci-bus.c
> +++ b/hw/s390x/s390-pci-bus.c
> @@ -1102,6 +1102,14 @@ static void s390_pcihost_reset(DeviceState *dev)
>  {
>      S390pciState *s = S390_PCI_HOST_BRIDGE(dev);
>      PCIBus *bus = s->parent_obj.bus;
> +    S390PCIBusDevice *pbdev, *next;
> +
> +    /* Unplug all pending devices that were requested to be released */
> +    QTAILQ_FOREACH_SAFE(pbdev, &s->zpci_devs, link, next) {
> +        if (pbdev->release_timer) {
> +            s390_pcihost_timer_cb(pbdev);
> +        }
> +    }
>  
>      s->bus_no = 0;
>      pci_for_each_device(bus, pci_bus_num(bus), s390_pci_enumerate_bridge, s);