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[79.180.2.31]) by smtp.gmail.com with ESMTPSA id a6sm2831755wmj.23.2021.02.23.05.26.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 23 Feb 2021 05:26:37 -0800 (PST) Date: Tue, 23 Feb 2021 08:26:34 -0500 From: "Michael S. Tsirkin" To: Jason Wang Subject: Re: [PATCH] vdpa/mlx5: set_features should allow reset to zero Message-ID: <20210223082536-mutt-send-email-mst@kernel.org> References: <1613735698-3328-1-git-send-email-si-wei.liu@oracle.com> <605e7d2d-4f27-9688-17a8-d57191752ee7@redhat.com> <20210222023040-mutt-send-email-mst@kernel.org> <22fe5923-635b-59f0-7643-2fd5876937c2@oracle.com> MIME-Version: 1.0 In-Reply-To: Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mst@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Disposition: inline Cc: Si-Wei Liu , netdev@vger.kernel.org, elic@nvidia.com, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org X-BeenThere: virtualization@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Linux virtualization List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 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[79.180.2.31]) by smtp.gmail.com with ESMTPSA id a6sm2831755wmj.23.2021.02.23.05.26.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 23 Feb 2021 05:26:37 -0800 (PST) Date: Tue, 23 Feb 2021 08:26:34 -0500 From: "Michael S. Tsirkin" To: Jason Wang Cc: Si-Wei Liu , elic@nvidia.com, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org Subject: Re: [PATCH] vdpa/mlx5: set_features should allow reset to zero Message-ID: <20210223082536-mutt-send-email-mst@kernel.org> References: <1613735698-3328-1-git-send-email-si-wei.liu@oracle.com> <605e7d2d-4f27-9688-17a8-d57191752ee7@redhat.com> <20210222023040-mutt-send-email-mst@kernel.org> <22fe5923-635b-59f0-7643-2fd5876937c2@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Feb 23, 2021 at 10:03:57AM +0800, Jason Wang wrote: > > On 2021/2/23 9:12 上午, Si-Wei Liu wrote: > > > > > > On 2/21/2021 11:34 PM, Michael S. Tsirkin wrote: > > > On Mon, Feb 22, 2021 at 12:14:17PM +0800, Jason Wang wrote: > > > > On 2021/2/19 7:54 下午, Si-Wei Liu wrote: > > > > > Commit 452639a64ad8 ("vdpa: make sure set_features is invoked > > > > > for legacy") made an exception for legacy guests to reset > > > > > features to 0, when config space is accessed before features > > > > > are set. We should relieve the verify_min_features() check > > > > > and allow features reset to 0 for this case. > > > > > > > > > > It's worth noting that not just legacy guests could access > > > > > config space before features are set. For instance, when > > > > > feature VIRTIO_NET_F_MTU is advertised some modern driver > > > > > will try to access and validate the MTU present in the config > > > > > space before virtio features are set. > > > > > > > > This looks like a spec violation: > > > > > > > > " > > > > > > > > The following driver-read-only field, mtu only exists if > > > > VIRTIO_NET_F_MTU is > > > > set. > > > > This field specifies the maximum MTU for the driver to use. > > > > " > > > > > > > > Do we really want to workaround this? > > > > > > > > Thanks > > > And also: > > > > > > The driver MUST follow this sequence to initialize a device: > > > 1. Reset the device. > > > 2. Set the ACKNOWLEDGE status bit: the guest OS has noticed the device. > > > 3. Set the DRIVER status bit: the guest OS knows how to drive the > > > device. > > > 4. Read device feature bits, and write the subset of feature bits > > > understood by the OS and driver to the > > > device. During this step the driver MAY read (but MUST NOT write) > > > the device-specific configuration > > > fields to check that it can support the device before accepting it. > > > 5. Set the FEATURES_OK status bit. The driver MUST NOT accept new > > > feature bits after this step. > > > 6. Re-read device status to ensure the FEATURES_OK bit is still set: > > > otherwise, the device does not > > > support our subset of features and the device is unusable. > > > 7. Perform device-specific setup, including discovery of virtqueues > > > for the device, optional per-bus setup, > > > reading and possibly writing the device’s virtio configuration > > > space, and population of virtqueues. > > > 8. Set the DRIVER_OK status bit. At this point the device is “live”. > > > > > > > > > so accessing config space before FEATURES_OK is a spec violation, right? > > It is, but it's not relevant to what this commit tries to address. I > > thought the legacy guest still needs to be supported. > > > > Having said, a separate patch has to be posted to fix the guest driver > > issue where this discrepancy is introduced to virtnet_validate() (since > > commit fe36cbe067). But it's not technically related to this patch. > > > > -Siwei > > > I think it's a bug to read config space in validate, we should move it to > virtnet_probe(). > > Thanks I take it back, reading but not writing seems to be explicitly allowed by spec. So our way to detect a legacy guest is bogus, need to think what is the best way to handle this. > > > > > > > > > > > > > > Rejecting reset to 0 > > > > > prematurely causes correct MTU and link status unable to load > > > > > for the very first config space access, rendering issues like > > > > > guest showing inaccurate MTU value, or failure to reject > > > > > out-of-range MTU. > > > > > > > > > > Fixes: 1a86b377aa21 ("vdpa/mlx5: Add VDPA driver for > > > > > supported mlx5 devices") > > > > > Signed-off-by: Si-Wei Liu > > > > > --- > > > > >    drivers/vdpa/mlx5/net/mlx5_vnet.c | 15 +-------------- > > > > >    1 file changed, 1 insertion(+), 14 deletions(-) > > > > > > > > > > diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c > > > > > b/drivers/vdpa/mlx5/net/mlx5_vnet.c > > > > > index 7c1f789..540dd67 100644 > > > > > --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c > > > > > +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c > > > > > @@ -1490,14 +1490,6 @@ static u64 > > > > > mlx5_vdpa_get_features(struct vdpa_device *vdev) > > > > >        return mvdev->mlx_features; > > > > >    } > > > > > -static int verify_min_features(struct mlx5_vdpa_dev *mvdev, > > > > > u64 features) > > > > > -{ > > > > > -    if (!(features & BIT_ULL(VIRTIO_F_ACCESS_PLATFORM))) > > > > > -        return -EOPNOTSUPP; > > > > > - > > > > > -    return 0; > > > > > -} > > > > > - > > > > >    static int setup_virtqueues(struct mlx5_vdpa_net *ndev) > > > > >    { > > > > >        int err; > > > > > @@ -1558,18 +1550,13 @@ static int > > > > > mlx5_vdpa_set_features(struct vdpa_device *vdev, u64 > > > > > features) > > > > >    { > > > > >        struct mlx5_vdpa_dev *mvdev = to_mvdev(vdev); > > > > >        struct mlx5_vdpa_net *ndev = to_mlx5_vdpa_ndev(mvdev); > > > > > -    int err; > > > > >        print_features(mvdev, features, true); > > > > > -    err = verify_min_features(mvdev, features); > > > > > -    if (err) > > > > > -        return err; > > > > > - > > > > >        ndev->mvdev.actual_features = features & > > > > > ndev->mvdev.mlx_features; > > > > >        ndev->config.mtu = cpu_to_mlx5vdpa16(mvdev, ndev->mtu); > > > > >        ndev->config.status |= cpu_to_mlx5vdpa16(mvdev, > > > > > VIRTIO_NET_S_LINK_UP); > > > > > -    return err; > > > > > +    return 0; > > > > >    } > > > > >    static void mlx5_vdpa_set_config_cb(struct vdpa_device > > > > > *vdev, struct vdpa_callback *cb) > >