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Tsirkin" To: Gerd Hoffmann Subject: Re: [PATCH 6/6] pcie: expire pending delete Message-ID: <20211012025611-mutt-send-email-mst@kernel.org> References: <20211011120504.254053-1-kraxel@redhat.com> <20211011120504.254053-7-kraxel@redhat.com> <20211011084310-mutt-send-email-mst@kernel.org> <20211012053034.faskn5y6b2hbbfys@sirius.home.kraxel.org> <20211012014515-mutt-send-email-mst@kernel.org> <20211012064445.ur4ihnuaftzn76wc@sirius.home.kraxel.org> MIME-Version: 1.0 In-Reply-To: <20211012064445.ur4ihnuaftzn76wc@sirius.home.kraxel.org> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mst@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=216.205.24.124; envelope-from=mst@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -28 X-Spam_score: -2.9 X-Spam_bar: -- X-Spam_report: (-2.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.049, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, 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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Paolo Bonzini , Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= , qemu-devel@nongnu.org, Eduardo Habkost Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, Oct 12, 2021 at 08:44:45AM +0200, Gerd Hoffmann wrote: > On Tue, Oct 12, 2021 at 01:46:35AM -0400, Michael S. Tsirkin wrote: > > On Tue, Oct 12, 2021 at 07:30:34AM +0200, Gerd Hoffmann wrote: > > > > > index f3ac04399969..477c8776aa27 100644 > > > > > --- a/hw/pci/pcie.c > > > > > +++ b/hw/pci/pcie.c > > > > > @@ -549,6 +549,8 @@ void pcie_cap_slot_unplug_request_cb(HotplugHandler *hotplug_dev, > > > > > } > > > > > > > > > > dev->pending_deleted_event = true; > > > > > + dev->pending_deleted_expires_ms = > > > > > + qemu_clock_get_ms(QEMU_CLOCK_VIRTUAL) + 5000; /* 5 secs */ > > > > > > > > > > /* In case user cancel the operation of multi-function hot-add, > > > > > * remove the function that is unexposed to guest individually, > > > > > > > > > > > > Well this will be barely enough, right? > > > > > > > > Once the Power > > > > Indicator begins blinking, a 5-second abort interval exists during which a second depression of the > > > > Attention Button cancels the operation. > > > > > > Well, canceling the hot-plug is not supported in qemu right now (there > > > is no qmp command for that). I'm also not sure it makes sense in the > > > first place for virtual machines. > > > > Yes. However if you resend an attention button press within the > > 5 second window, guest will think you cancelled hot-plug > > and act accordingly. > > It's a fundamentally racy algorithm :( > > That's why re-sending an attention button press is blocked > for 5 seconds. > It's also blocked in case the guest blinks the power > indicator (see patch #3). > > Both together work well in my testing, I can flood a (linux) guest > with device_del commands without bad side effects: > > First device_del command sends attention button press. > Then device_del is rejected because the 5 secs are not over yet. > Then device_del is rejected because the indicator blinks. Ah, I see. 5 secs is a lot so yea, most likely it's gonnu be ok, worst case we'll wait another 5 seconds and send again, right? Worth checking with windows guests BTW, we saw lots of races with these too. > Then unplug completes (and qemu sends event). > Then device_del fails because the device doesn't exist any more. > > take care, > Gerd