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[99.254.121.117]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-44fe8199a6fsm12669731cf.58.2024.07.26.04.32.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 26 Jul 2024 04:32:44 -0700 (PDT) Date: Fri, 26 Jul 2024 07:32:41 -0400 From: Peter Xu To: "Michael S. Tsirkin" Cc: Thomas Huth , Yuri Benditovich , eduardo@habkost.net, marcel.apfelbaum@gmail.com, philmd@linaro.org, wangyanan55@huawei.com, dmitry.fleytman@gmail.com, akihiko.odaki@daynix.com, jasowang@redhat.com, sriram.yagnaraman@est.tech, sw@weilnetz.de, qemu-devel@nongnu.org, yan@daynix.com, Fabiano Rosas , Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= , devel@lists.libvirt.org Subject: Re: [PATCH v2 4/4] virtio-net: Add support for USO features Message-ID: References: <20230731223148.1002258-1-yuri.benditovich@daynix.com> <20230731223148.1002258-5-yuri.benditovich@daynix.com> <20240726020656-mutt-send-email-mst@kernel.org> <775ff713-f7d3-4fdc-8ba0-4ebde577040d@redhat.com> <20240726032520-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20240726032520-mutt-send-email-mst@kernel.org> Received-SPF: pass client-ip=170.10.133.124; envelope-from=peterx@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.143, 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: 2.1.29 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, Jul 26, 2024 at 03:25:31AM -0400, Michael S. Tsirkin wrote: > On Fri, Jul 26, 2024 at 09:03:24AM +0200, Thomas Huth wrote: > > On 26/07/2024 08.08, Michael S. Tsirkin wrote: > > > On Thu, Jul 25, 2024 at 06:18:20PM -0400, Peter Xu wrote: > > > > On Tue, Aug 01, 2023 at 01:31:48AM +0300, Yuri Benditovich wrote: > > > > > USO features of virtio-net device depend on kernel ability > > > > > to support them, for backward compatibility by default the > > > > > features are disabled on 8.0 and earlier. > > > > > > > > > > Signed-off-by: Yuri Benditovich > > > > > Signed-off-by: Andrew Melnychecnko > > > > > > > > Looks like this patch broke migration when the VM starts on a host that has > > > > USO supported, to another host that doesn't.. > > > > > > This was always the case with all offloads. The answer at the moment is, > > > don't do this. > > > > May I ask for my understanding: > > "don't do this" = don't automatically enable/disable virtio features in QEMU > > depending on host kernel features, or "don't do this" = don't try to migrate > > between machines that have different host kernel features? > > The later. The question is how should an user know a migration is not supported? The user can be using exactly the same QEMU binary on two hosts, while there can be a tiny slight difference in host kernel version, then migration can fail between them misterously. There're too many kernel features that can be on/off when kernels are different, even if slightly. Then I don't see how someone can even identify such issue, unless one uses exactly the same host kernels on both sides.. -- Peter Xu