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Tsirkin" To: Igor Mammedov Subject: Re: [PATCH] pci: Refuse to hotplug PCI Devices when the Guest OS is not ready Message-ID: <20201027085650-mutt-send-email-mst@kernel.org> References: <20201022100028-mutt-send-email-mst@kernel.org> <20201022102857-mutt-send-email-mst@kernel.org> <20201022110016-mutt-send-email-mst@kernel.org> <20201026174537.128a4173@yekko.fritz.box> <20201027072430-mutt-send-email-mst@kernel.org> <20201027135426.765dd19b@redhat.com> MIME-Version: 1.0 In-Reply-To: <20201027135426.765dd19b@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 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=63.128.21.124; envelope-from=mst@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/10/27 01:06:07 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] 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_H5=0.001, RCVD_IN_MSPIKE_WL=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: David Gibson , Julia Suvorova , qemu devel list Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, Oct 27, 2020 at 01:54:26PM +0100, Igor Mammedov wrote: > On Tue, 27 Oct 2020 07:26:44 -0400 > "Michael S. Tsirkin" wrote: > > > On Mon, Oct 26, 2020 at 05:45:37PM +1100, David Gibson wrote: > > > On Fri, 23 Oct 2020 09:26:48 +0300 > > > Marcel Apfelbaum wrote: > > > > > > > Hi Michael, > > > > > > > > On Thu, Oct 22, 2020 at 6:01 PM Michael S. Tsirkin wrote: > > > > > > > > [...] > [...] > > > > Simplistic does not mean wrong or incorrect. > > > > I fail to see why it is not enough. > > > > > > > > What QEMU can do better? Wait an unbounded time for the blinking to finish? > > > > > > It certainly shouldn't wait an unbounded time. But a wait with timeout > > > seems worth investigating to me. > racy, timeout is bound to break once it's in overcommited env. > > > If it's helpful, I'd add a query to check state > > so management can figure out why doesn't guest see device yet. > that means mgmt would have to poll it and forward it to user > somehow. > > > But otherwise just buffer the request until such time as > > we can deliver it to guest ... > I have more questions wrt the suggestion/workflow: > * at what place would you suggest buffering it? PCIESlot maybe? > * what would be the request in this case, i.e. create PCI device anyways > and try to signal hotplug event later? that was my idea, yes. > * what would baremethal do in such case? exactly the same, human would wait until blinking stops. > * what to do in case guest is never ready, what user should do in such case? As in guest is stuck? Do we care? It can't use the device. > * can be such device be removed? why not? device_del could complete immediately ... > not sure that all of this is worth of the effort and added complexity. > > alternatively: > maybe ports can send QMP events about it's state changes, which end user would > be able to see + error like in this patch. > > On top of it, mgmt could build a better UIx, like retry/notify logic if > that's what user really wishes for and configures (it would be up to user to > define behaviour). I'd say let's get expected behaviour for existing commands first. We can add events and stuff on top. > > > > What if we have a buggy guest with a kernel stuck in blinking? > > > > Is QEMU's responsibility to emulate the operator itself? Because the > > > > operator > > > > is the one who is supposed to wait. > > > > > > > > > > > > Thanks, > > > > Marcel > > > > > > > > [...] > > > > > > > > > -- > > > David Gibson > > > Principal Software Engineer, Virtualization, Red Hat > > > > > >