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([2a0d:3344:2712:7e10:4d59:d956:544f:d65c]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4586918c6c4sm19960055e9.11.2025.07.23.04.21.31 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 23 Jul 2025 04:21:31 -0700 (PDT) Message-ID: Date: Wed, 23 Jul 2025 13:21:30 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC v3 06/13] virtio-pci: implement support for extended features To: Jason Wang Cc: qemu-devel@nongnu.org, Paolo Bonzini , Dmitry Fleytman , Akihiko Odaki , Sriram Yagnaraman , "Michael S. Tsirkin" , Stefano Garzarella , Cornelia Huck , Luigi Rizzo , Giuseppe Lettieri , Vincenzo Maffione , Eric Blake , Markus Armbruster References: <253cd85bc76ded8259fc9d12ed3764e2507bcb75.1752828082.git.pabeni@redhat.com> <6a1e2b06-4f4f-45b7-8875-ecb60f74aa8d@redhat.com> Content-Language: en-US From: Paolo Abeni In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=pabeni@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -24 X-Spam_score: -2.5 X-Spam_bar: -- X-Spam_report: (-2.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.377, 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_H5=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 7/23/25 7:47 AM, Jason Wang wrote: > On Tue, Jul 22, 2025 at 3:37 PM Paolo Abeni wrote: >> >> On 7/22/25 5:28 AM, Jason Wang wrote: >>> On Fri, Jul 18, 2025 at 4:53 PM Paolo Abeni wrote: >>>> >>>> Extend the features configuration space to 128 bits, and allow the >>>> common read/write operation to access all of it. >>>> >>>> On migration, save the 128 bit version of the features only if the >>>> upper bits are non zero. Relay reset to clear all the feature >>>> space before load. >>>> >>>> Signed-off-by: Paolo Abeni >>> >>> This is a guest noticeable behaviour change. I wonder if we need a >>> command line option to enable and disable this feature for migration >>> compatibility. >> >> This point is not clear to me, could you please elaborate a bit more? do >> you mean we need i.e. a DEFINE_PROP_BOOL() or the like to enable the 128 >> bit space usage? > > Yes, or maybe have a way to let the device to enable it automatically > E.g when UDP GSO is enabled for virtio-net. I think we can safely enable the extended space access (read/write) if virtio_features_use_ex(vdev->host_features_ex). That should cover also any eventual future addition of more extended features - even of different devices. /P