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[79.180.2.31]) by smtp.gmail.com with ESMTPSA id e17sm9660537wro.36.2021.02.23.04.26.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 23 Feb 2021 04:26:31 -0800 (PST) Date: Tue, 23 Feb 2021 07:26:28 -0500 From: "Michael S. Tsirkin" To: Si-Wei Liu Cc: jasowang@redhat.com, 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: <20210223072047-mutt-send-email-mst@kernel.org> References: <1613735698-3328-1-git-send-email-si-wei.liu@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1613735698-3328-1-git-send-email-si-wei.liu@oracle.com> Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Fri, Feb 19, 2021 at 06:54:58AM -0500, 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. 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") isn't this more vdpa: make sure set_features is invoked for legacy > Signed-off-by: Si-Wei Liu I think we at least need to correct the comment in include/linux/vdpa.h then Instead of "we assume a legacy guest" we'd say something like "call set features in case it's a legacy guest". Generally it's unfortunate. Need to think about what to do here. Any idea how else we can cleanly detect a legacy guest? > --- > 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; Let's just set VIRTIO_F_ACCESS_PLATFORM in core? Then we don't need to hack mlx5 ... > @@ -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) > -- > 1.8.3.1