Re: [PATCH v3] acpi: pcihp: make pending delete blocking action expire

[Gerd Hoffmann]

On Wed, Apr 05, 2023 at 11:42:56AM +0200, Igor Mammedov wrote:
> with Q35 using ACPI PCI hotplug by default, user's request to unplug
> device is ignored when it's issued before guest OS has been booted.
> And any additional attempt to request device hot-unplug afterwards
> results in following error:
> 
>   "Device XYZ is already in the process of unplug"
> 
> arguably it can be considered as a regression introduced by [2],
> before which it was possible to issue unplug request multiple
> times.
> 
> Allowing pending delete blocking expire brings ACPI PCI hotplug
> on par with native PCIe unplug behavior [1] and allows user
> to repeat unplug requests at propper times.
> Set expire timeout to arbitrary 1msec so user won't be able to
> flood guest with SCI interrupts by calling device_del in tight loop.
> 
> PS:
> ACPI spec doesn't mandate what OSPM can do with GPEx.status
> bits set before it's booted => it's impl. depended.
> Status bits may be retained (I tested with one Windows version)
> or cleared (Linux since 2.6 kernel times) during guest's ACPI
> subsystem initialization.
> Clearing status bits (though not wrong per se) hides the unplug
> event from guest, and it's upto user to repeat device_del later
> when guest is able to handle unplug requests.
> 
> 1) 18416c62e3 ("pcie: expire pending delete")
> 2)
> Fixes: cce8944cc9ef ("qdev-monitor: Forbid repeated device_del")
> Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> CC: mst@redhat.com
> CC: anisinha@redhat.com
> CC: jusual@redhat.com
> CC: kraxel@redhat.com

Acked-by: Gerd Hoffmann <kraxel@redhat.com>