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Tsirkin" , Jason Wang , eduardo@habkost.net, marcel.apfelbaum@gmail.com, philmd@linaro.org, wangyanan55@huawei.com, zhao1.liu@intel.com, qemu-devel@nongnu.org, farosas@suse.de, jinpu.wang@ionos.com, berrange@redhat.com Subject: Re: [RFC PATCH] virtio-net: introduce strict peer feature check Message-ID: References: <20251107020149.3223-1-jasowang@redhat.com> <20251113110004-mutt-send-email-mst@kernel.org> <20251113114710-mutt-send-email-mst@kernel.org> <20251113124207-mutt-send-email-mst@kernel.org> <6a83ca08-5484-469a-8020-a1165aed1c73@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <6a83ca08-5484-469a-8020-a1165aed1c73@redhat.com> Received-SPF: pass client-ip=170.10.129.124; envelope-from=peterx@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_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_PASS=-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 Fri, Nov 14, 2025 at 06:48:42AM +0100, Thomas Huth wrote: > On 13/11/2025 20.32, Peter Xu wrote: > > On Thu, Nov 13, 2025 at 12:46:55PM -0500, Michael S. Tsirkin wrote: > > > failing to start a perfectly good qemu which used to work > > > because you changed kernels is better than failing to migrate how? > > > > > > > I agree this is not pretty. > > > > The very original proposal was having extra features to be OFF by default, > > only allow explicit selections to enable them when the mgmt / user is aware > > of the possible hosts to run on top. > > Could it maybe be tied to the "-nodefaults" option of QEMU? If you run QEMU > with "-nodefaults" (which you should do when planning a migration later), > these extra features that depend on the kernel version stay OFF. If you run > QEMU without "-nodefaults", QEMU could enable them if supported by the > kernel. So that would benefit both, the people running QEMU via management > layers (using -nodefaults), and the people who just want to quickly launch > QEMU on the command line. WDYT? Are the "default set of devices" when without -nodefaults more or less stable (aka, still live migratable)? If so, I wonder if there're still people relying on migrations but using default devices. The other question is, such proposal also means auto-probe will be OFF for all serious users. I am personally OK with such, however it means it'll also reduce the test coverage that Michael was looking for on new network features, when QEMU is running on new kernels. Thanks, -- Peter Xu