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Tsirkin" To: Ani Sinha Subject: Re: [PATCH-for-6.2] docs: add a word of caution on x-native-hotplug property for pcie-root-ports Message-ID: <20211125154927-mutt-send-email-mst@kernel.org> References: <20211125120629.187014-1-ani@anisinha.ca> MIME-Version: 1.0 In-Reply-To: <20211125120629.187014-1-ani@anisinha.ca> 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=170.10.129.124; envelope-from=mst@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.7, 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_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: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: imammedo@redhat.com, qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, Nov 25, 2021 at 05:36:29PM +0530, Ani Sinha wrote: > x-native-hotplug property, when used in order to disable HPC bit on the PCIE > root ports, can lead to unexpected results from the guest operating system. > Users are strongly advised not to touch this property in order to manipulte the > HPC bit. Add a word of caution in the pcie.txt doc file to document this. > > Signed-off-by: Ani Sinha Do we want to generally document this for all "x-" options? > --- > docs/pcie.txt | 17 ++++++++++++++++- > 1 file changed, 16 insertions(+), 1 deletion(-) > > diff --git a/docs/pcie.txt b/docs/pcie.txt > index 89e3502075..e1f99f725f 100644 > --- a/docs/pcie.txt > +++ b/docs/pcie.txt > @@ -262,11 +262,26 @@ PCI Express Root Ports (and PCI Express Downstream Ports). > Port, which may come handy for hot-plugging another device. > > > -5.3 Hot-plug example: > +5.2 Hot-plug example: > Using HMP: (add -monitor stdio to QEMU command line) > device_add ,id=,bus= > > > +5.3 A word of caution using hotplug on PCI Express Root Ports: > +Starting Qemu version 6.2, PCI Express Root ports have a property > +"x-native-hotplug" ("native-hotplug" for Qemu version 6.1), that can be used to > +enable or disable hotplug on that port. For example: > + > +-device pcie-root-port,x-native-hotplug=off,... etc. > + > +The "x-" prefix indicates that this property is highly experimental and can > +lead to unexpected results from the guest operating system if users try to use > +it to alter the native hotplug on the port. It also means that the property > +name and its behavior is liable to change in the future and is not expected to > +be stable across Qemu versions. Therefore, end users are advised not to change > +the value of this option from its default set value or use it in the Qemu > +command line. > + > 6. Device assignment > ==================== > Host devices are mostly PCI Express and should be plugged only into > -- > 2.25.1