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Tsirkin" To: Igor Mammedov Cc: qemu-devel@nongnu.org, anisinha@redhat.com, jusual@redhat.com, kraxel@redhat.com Subject: Re: [PATCH v2] acpi: pcihp: make pending delete blocking action expire Message-ID: <20230405044231-mutt-send-email-mst@kernel.org> References: <20230405083444.1536720-1-imammedo@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230405083444.1536720-1-imammedo@redhat.com> Received-SPF: pass client-ip=170.10.129.124; envelope-from=mst@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Wed, Apr 05, 2023 at 10:34:44AM +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 I feel a real solution is to detect guest handling the event such as clearing GPE and allowing resending the interrupt then. A similar strategy should be possible with the attention button. This patch is more of a band-aid - it is possible that guest rebooted and so user knows a new device_del is required, and we arbitrarily reject that. Right? This is arguably a regression but not in this release yes? So I don't think it needs to block qemu release. > --- > v2: > * change timeout to 1ms > * add comment to expire usage > * massage commit message to be a bit more clear > > CC: mst@redhat.com > CC: anisinha@redhat.com > CC: jusual@redhat.com > CC: kraxel@redhat.com It's helpful to have CC before --- so backporters know whom to CC, too. > --- > hw/acpi/pcihp.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/hw/acpi/pcihp.c b/hw/acpi/pcihp.c > index dcfb779a7a..5daa732a33 100644 > --- a/hw/acpi/pcihp.c > +++ b/hw/acpi/pcihp.c > @@ -357,6 +357,16 @@ void acpi_pcihp_device_unplug_request_cb(HotplugHandler *hotplug_dev, > * acpi_pcihp_eject_slot() when the operation is completed. > */ > pdev->qdev.pending_deleted_event = true; > + /* if unplug was requested before OSPM is initialized, > + * linux kernel will clear GPE0.sts[] bits during boot, which effectively > + * hides unplug event. BAnd than followup qmp_device_del() calls remain BAnd? > + * blocked by above flag permanently. > + * Unblock qmp_device_del() by setting expire limit, so user can > + * repeat unplug request later when OSPM has been booted. > + */ > + pdev->qdev.pending_deleted_expires_ms = > + qemu_clock_get_ms(QEMU_CLOCK_VIRTUAL); /* 1 msec */ > + > s->acpi_pcihp_pci_status[bsel].down |= (1U << slot); > acpi_send_event(DEVICE(hotplug_dev), ACPI_PCI_HOTPLUG_STATUS); > } > -- > 2.39.1