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Tue, 18 May 2021 10:20:53 +0000 (UTC) MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Date: Tue, 18 May 2021 10:06:21 -0000 From: Thomas Huth <1924603@bugs.launchpad.net> To: qemu-devel@nongnu.org X-Launchpad-Notification-Type: bug X-Launchpad-Bug: product=qemu; status=Invalid; importance=Undecided; assignee=None; X-Launchpad-Bug-Tags: v5.1.0 X-Launchpad-Bug-Information-Type: Public X-Launchpad-Bug-Private: no X-Launchpad-Bug-Security-Vulnerability: no X-Launchpad-Bug-Commenters: gdawar th-huth X-Launchpad-Bug-Reporter: Gautam Dawar (gdawar) X-Launchpad-Bug-Modifier: Thomas Huth (th-huth) References: <161851052657.18499.4390060645724242620.malonedeb@wampee.canonical.com> Message-Id: <162133238149.8616.8027273223904234916.malone@gac.canonical.com> Subject: [Bug 1924603] Re: Incorrect feature negotiation for vhost-vdpa netdevice X-Launchpad-Message-Rationale: Subscriber (QEMU) @qemu-devel-ml X-Launchpad-Message-For: qemu-devel-ml Precedence: bulk X-Generated-By: Launchpad (canonical.com); Revision="5321c3f40fa4d4b847f4e47fb766e7b95ed5036c"; Instance="production" X-Launchpad-Hash: 37dcfdf879db1f25323eeced04f8a3c96dd9803a Received-SPF: none client-ip=91.189.90.7; envelope-from=bounces@canonical.com; helo=indium.canonical.com X-Spam_score_int: -65 X-Spam_score: -6.6 X-Spam_bar: ------ X-Spam_report: (-6.6 / 5.0 requ) BAYES_00=-1.9, HEADER_FROM_DIFFERENT_DOMAINS=0.249, RCVD_IN_DNSWL_HI=-5, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_NONE=0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Bug 1924603 <1924603@bugs.launchpad.net> Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Not sure who should be the assignee here ... maybe it's best if you write a mail to the people who have been involved in the original code (see https://gitlab.com/qemu-project/qemu/-/commit/108a64818e69be0a97c ) and ask them who could have a look at this issue. -- = You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. https://bugs.launchpad.net/bugs/1924603 Title: Incorrect feature negotiation for vhost-vdpa netdevice Status in QEMU: Invalid Bug description: QEMU cmdline: =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D ./x86_64-softmmu/qemu-system-x86_64 -machine accel=3Dkvm -m 2G -hda /gau= tam/centos75_1.qcow2 -name gautam,process=3Dgautam -enable-kvm -netdev vhos= t-vdpa,id=3Dmynet0,vhostdev=3D/dev/vhost-vdpa-0 -device virtio-net-pci,netd= ev=3Dmynet0,mac=3D02:AA:BB:DD:00:20,disable-modern=3Doff,page-per-vq=3Don -= cpu host --nographic Host OS: =3D=3D=3D=3D=3D=3D=3D=3D Linux kernel 5.11 running on x86 host Guest OS: =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D CentOS 7.5 Root cause analysis: =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D For vhost-vdpa netdevice, the feature negotiation results in sending the superset of features received from device in call to get_features vdpa ops callback. During the feature-negotiation phase, the acknowledged feature bits are initialized with backend_features and then checked for supported feature bits in vhost_ack_features(): void vhost_net_ack_features(struct vhost_net *net, uint64_t features) { net->dev.acked_features =3D net->dev.backend_features; vhost_ack_features(&net->dev, vhost_net_get_feature_bits(net), features= ); } = The vhost_ack_features() function just builds up on the dev.acked_feature= s and never trims it down: void vhost_ack_features(struct vhost_dev *hdev, const int *feature_bits, = uint64_t features) { const int *bit =3D feature_bits; while (*bit !=3D VHOST_INVALID_FEATURE_BIT) { uint64_t bit_mask =3D (1ULL << *bit); = if (features & bit_mask) hdev->acked_features |=3D bit_mask; bit++; } } Because of this hdev->acked_features is always minimally equal to the value of device features and this is the value that is passed to the device in set_features callback: static int vhost_dev_set_features(struct vhost_dev *dev, bool enable_log) { uint64_t *features =3D dev->acked_features; ..... r =3D dev->vhost_ops->*vhost_set_features*(dev, features); } To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/1924603/+subscriptions