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Tsirkin" To: Igor Mammedov Cc: qemu-devel@nongnu.org, anisinha@redhat.com, jusual@redhat.com, kraxel@redhat.com, pbonzini@redhat.com Subject: Re: [PATCH] acpi: pcihp: make pending delete expire in 5sec Message-ID: <20230404104122-mutt-send-email-mst@kernel.org> References: <20230403161618.1344414-1-imammedo@redhat.com> <20230403131833-mutt-send-email-mst@kernel.org> <20230404102807.4626b0be@imammedo.users.ipa.redhat.com> <20230404084603-mutt-send-email-mst@kernel.org> <20230404160435.45c2513d@imammedo.users.ipa.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230404160435.45c2513d@imammedo.users.ipa.redhat.com> Received-SPF: pass client-ip=170.10.133.124; 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 Tue, Apr 04, 2023 at 04:04:35PM +0200, Igor Mammedov wrote: > On Tue, 4 Apr 2023 08:46:15 -0400 > "Michael S. Tsirkin" wrote: > > > On Tue, Apr 04, 2023 at 10:28:07AM +0200, Igor Mammedov wrote: > > > On Mon, 3 Apr 2023 13:23:45 -0400 > > > "Michael S. Tsirkin" wrote: > > > > > > > On Mon, Apr 03, 2023 at 06:16:18PM +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 expire brings ACPI PCI hotplug on par > > > > > with native PCIe unplug behavior [1] which in its turn refers > > > > > back to ACPI PCI hotplug ability to repeat unplug requests. > > > > > > > > > > PS: > > > > > >From ACPI point of view, unplug request sets PCI hotplug status > > > > > bit in GPE0 block. However depending on OSPM, status bits may > > > > > be retained (Windows) or cleared (Linux) during guest's ACPI > > > > > subsystem initialization, and as result Linux guest looses > > > > > plug/unplug event (no SCI generated) if plug/unplug has > > > > > happend before guest OS initialized GPE registers handling. > > > > > I couldn't find any restrictions wrt OPM clearing GPE status > > > > > bits ACPI spec. > > > > > Hence a fallback approach is to let user repeat unplug request > > > > > later at the time when guest OS has booted. > > > > > > > > > > 1) 18416c62e3 ("pcie: expire pending delete") > > > > > 2) > > > > > Fixes: cce8944cc9ef ("qdev-monitor: Forbid repeated device_del") > > > > > Signed-off-by: Igor Mammedov > > > > > > > > A bit concerned about how this interacts with failover, > > > > and 5sec is a lot of time that I hoped we'd avoid with acpi. > > > > Any better ideas of catching such misbehaving guests? > > > > > > It shouldn't affect affect failover, pending_delete is not > > > cleared after all (only device removal should do that). > > > So all patch does is allowing to reissue unplug request > > > in case it was lost, delay here doesn't mean much > > > (do you have any preference wrt specific value)? > > > > I'd prefer immediately. > > ok, lets use 1ms then, I'd rather reuse the preexisting > pending_deleted_expires_ms machinery instead of > special-casing immediate repeat. And just to make sure, are you working on fixing this in Linux at least? Because the work around is ok but it still causes latency. > > > > > As for 'misbehaving' - I tried to find justification > > > for it in spec, but I couldn't. > > > Essentially it's upto OSPM to clear or not GPE status > > > bits at startup (linux was doing it since forever), > > > depending on guest's ability to handle hotplug events > > > at boot time. > > > > > > It's more a user error, ACPI hotplug does imply booted > > > guest for it to function properly. So it's fine to > > > loose unplug event at boot time. What QEMU does wrong is > > > preventing follow up unplug requests. > > > > > > > > > > > Also at this point I do not know why we deny hotplug > > > > pending_deleted_event in qdev core. > > > > Commit log says: > > > > > > > > Device unplug can be done asynchronously. Thus, sending the second > > > > device_del before the previous unplug is complete may lead to > > > > unexpected results. On PCIe devices, this cancels the hot-unplug > > > > process. > > > > > > > > so it's a work around for an issue in pcie hotplug (and maybe shpc > > > > too?). Maybe we should have put that check in pcie/shpc and > > > > leave acpi along? > > > > > > > > > > > > > > > > > > > > > --- > > > > > CC: mst@redhat.com > > > > > CC: anisinha@redhat.com > > > > > CC: jusual@redhat.com > > > > > CC: kraxel@redhat.com > > > > > --- > > > > > hw/acpi/pcihp.c | 2 ++ > > > > > 1 file changed, 2 insertions(+) > > > > > > > > > > diff --git a/hw/acpi/pcihp.c b/hw/acpi/pcihp.c > > > > > index dcfb779a7a..cd4f9fee0a 100644 > > > > > --- a/hw/acpi/pcihp.c > > > > > +++ b/hw/acpi/pcihp.c > > > > > @@ -357,6 +357,8 @@ 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; > > > > > + pdev->qdev.pending_deleted_expires_ms = > > > > > + qemu_clock_get_ms(QEMU_CLOCK_VIRTUAL) + 5000; /* 5 secs */ > > > > > s->acpi_pcihp_pci_status[bsel].down |= (1U << slot); > > > > > acpi_send_event(DEVICE(hotplug_dev), ACPI_PCI_HOTPLUG_STATUS); > > > > > } > > > > > -- > > > > > 2.39.1 > > > > > >