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[79.176.118.93]) by smtp.gmail.com with ESMTPSA id z4sm357147wrg.53.2020.10.28.10.49.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 28 Oct 2020 10:49:25 -0700 (PDT) Date: Wed, 28 Oct 2020 13:49:22 -0400 From: "Michael S. Tsirkin" To: Igor Mammedov Subject: Re: [PATCH] pci: Refuse to hotplug PCI Devices when the Guest OS is not ready Message-ID: <20201028134816-mutt-send-email-mst@kernel.org> References: <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> <20201028143135.51c0a918@yekko.fritz.box> <20201028163945.64eacc81@redhat.com> MIME-Version: 1.0 In-Reply-To: <20201028163945.64eacc81@redhat.com> 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-detected-operating-system: by eggs.gnu.org: First seen = 2020/10/28 01:50:00 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_H4=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 Wed, Oct 28, 2020 at 04:39:45PM +0100, Igor Mammedov wrote: > On Wed, 28 Oct 2020 14:31:35 +1100 > David Gibson wrote: > > > On Tue, 27 Oct 2020 13:54:26 +0100 > > Igor Mammedov wrote: > > > > > On Tue, 27 Oct 2020 07:26:44 -0400 > > > "Michael S. Tsirkin" wrote: > > > > > > [...] > > > [...] > > > [...] > > > [...] > > > [...] > > > > > > > > > > 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. > > > > Hm. That's no less true at the management layer than it is at the qemu > > layer. > true, but it's user policy which is defined by user not by QEMU. > > > > > > > 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. > > > > If that even makes sense. In the case of Kata, it's supposed to be > > autonomously creating the VM, so there's nothing meaningful it can > > forward to the user other than "failed to create the container because > > of some hotplug problem that means nothing to you". > > > > > [...] > > > I have more questions wrt the suggestion/workflow: > > > * at what place would you suggest buffering it? > > > * what would be the request in this case, i.e. create PCI device anyways > > > and try to signal hotplug event later? > > > * what would baremethal do in such case? > > > * what to do in case guest is never ready, what user should do in such case? > > > * can be such device be removed? > > > > > > 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). > > > > That kind of makes sense if the user is explicitly requesting hotplugs, > > but that's not necessarily the case. > user doesn't have to be a human, it could be some mgmt layer that would > automate retry logic, depending on what actually user needs for particular task > (i.e. fail immediately, retry N time then fail, retry with time out - then fail, > don't care - succeed, ...). The point is for QEMU to provide means for mgmt to > implement whatever policy user would need. We are not coming up with new APIs here. Let's make existing ones work reliably first. We can talk about a flag where it fails instead of deferring hotplug, separately. > PS: > but then, I know close to nothing about PCI, so all of above might be nonsense.