Messages in this thread | | | Subject | Re: [PATCH] vdpa/mlx5: set_features should allow reset to zero | From | Jason Wang <> | Date | Tue, 23 Feb 2021 10:03:08 +0800 |
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On 2021/2/23 1:09 上午, Si-Wei Liu wrote: > > > On 2/21/2021 8:14 PM, 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? > > Isn't the commit 452639a64ad8 itself is a workaround for legacy guest?
Yes, but the problem is we can't detect whether or not it's an legacy guest (e.g feature is not set).
> > I think the point is, since there's legacy guest we'd have to support, > this host side workaround is unavoidable.
Since from vhost-vDPA point of view the driver is Qemu, it means we need make qemu vhost-vDPA driver spec complaint.
E.g how about:
1) revert 452639a64ad8 and fix Qemu? In Qemu, during vhost-vDPA initialization, do a minial config sync by neogitating minimal features (e.g just VIRTIO_F_ACCESS_PLATFORM). When FEATURE_OK is not set from guest, we can only allow it to access the config space that is emulated by Qemu?
Then
> Although I agree the violating driver should be fixed (yes, it's in > today's upstream kernel which exists for a while now).
2) Fix the virtio driver bug.
Or a quick workaround is to set (VIRTIO_F_ACCESS_PLATFORM instead of 0) in this case.
Thanks
> > -Siwei > >> >> Thanks >> >> >>> 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 <si-wei.liu@oracle.com> >>> --- >>> 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) >> >
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