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[80.230.39.63]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-42b53f0b513sm4830981f8f.30.2025.11.13.08.47.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 13 Nov 2025 08:47:54 -0800 (PST) Date: Thu, 13 Nov 2025 11:47:51 -0500 From: "Michael S. Tsirkin" To: Peter Xu Cc: 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, thuth@redhat.com, berrange@redhat.com Subject: Re: [RFC PATCH] virtio-net: introduce strict peer feature check Message-ID: <20251113114710-mutt-send-email-mst@kernel.org> References: <20251107020149.3223-1-jasowang@redhat.com> <20251113110004-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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: -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_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_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 Thu, Nov 13, 2025 at 11:37:25AM -0500, Peter Xu wrote: > On Thu, Nov 13, 2025 at 11:09:32AM -0500, Michael S. Tsirkin wrote: > > On Fri, Nov 07, 2025 at 10:01:49AM +0800, Jason Wang wrote: > > > We used to clear features silently in virtio_net_get_features() even > > > if it is required. This complicates the live migration compatibility > > > as the management layer may think the feature is enabled but in fact > > > not. > > > > > > Let's add a strict feature check to make sure if there's a mismatch > > > between the required feature and peer, fail the get_features() > > > immediately instead of waiting until the migration to fail. This > > > offload the migration compatibility completely to the management > > > layer. > > > > > > Signed-off-by: Jason Wang > > > > This is not really useful - how do users know how to tweak their > > command lines? > > We discussed this many times. > > To try and solve this you need a tool that will tell you how to start > > VM on X to make it migrateable to Y or Z. > > > > > > More importantly, > > migration is a niche thing and breaking booting perfectly good VMs > > just for that seems wrong. > > IMHO Jason's proposal is useful in that it now provides a way to provide > ABI stablility but allows auto-ON to exist. > > If we think migration is optional, we could add a migration blocker where > strict check flag is set to OFF, as I mentioned in the email reply to Dan. > As that implies the VM ABI is not guaranteed. > > Thanks, All you have to do is avoid changing the kernel and ABI is stable. Downstreams already do this. > > > > > > If you want to keep this off by default, and have management > > enable this if it knows what it's doing, then I don't really > > care. > > -- > Peter Xu