Re: [PATCH 1/1] pci/pcie: refuse another hotplug/unplug event if attention button is pending

[Michael S. Tsirkin]

On Wed, Jul 22, 2020 at 07:17:22PM +0300, Maxim Levitsky wrote:
> Curently it is possible to hotplug a device and then immediatly
> hotunplug it before the OS notices, and that will result
> in missed unplug event since we can only send one attention button event.
> 
> Moreover the device will stuck in unplugging state forever.
> 
> Error out in such cases and rely on the caller (e.g libvirt) to retry
> the unplug a bit later
> 
> Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
> ---
>  hw/pci/pcie.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/hw/pci/pcie.c b/hw/pci/pcie.c
> index 5b48bae0f6..9e836cf2f4 100644
> --- a/hw/pci/pcie.c
> +++ b/hw/pci/pcie.c
> @@ -402,6 +402,17 @@ static void pcie_cap_slot_plug_common(PCIDevice 
> *hotplug_dev, DeviceState *dev,
>           */
>          error_setg_errno(errp, EBUSY, "slot is electromechanically locked");
>      }
> +
> +    if (sltsta & PCI_EXP_SLTSTA_ABP) {
> +        /*
> +         * Attention button is pressed, thus we can't send another
> +         * hotpplug event

typo

> +         */
> +        error_setg_errno(errp, EBUSY,
> +                         "attention button is already pressed, can't "
> +                         "send another hotplug event");
> +    }
> +
>  }

It would be neater if we could queue the event up
in qemu. Alternatively - can we clean up the unhandled
event so guest does not even notice the device
briefly appeared?

>  
>  void pcie_cap_slot_pre_plug_cb(HotplugHandler *hotplug_dev, DeviceState *dev,
> -- 
> 2.26.2