On Wed, Feb 24, 2021 at 02:55:13PM +0800, Jason Wang wrote:
>
> On 2021/2/24 2:47 下午, Michael S. Tsirkin wrote:
> > On Wed, Feb 24, 2021 at 08:45:20AM +0200, Eli Cohen wrote:
> > > On Wed, Feb 24, 2021 at 12:17:58AM -0500, Michael S. Tsirkin wrote:
> > > > On Wed, Feb 24, 2021 at 11:20:01AM +0800, Jason Wang wrote:
> > > > > On 2021/2/24 3:35 上午, Si-Wei Liu wrote:
> > > > > >
> > > > > > On 2/23/2021 5:26 AM, Michael S. Tsirkin wrote:
> > > > > > > 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.
> > > > > > Then maybe revert commit fe36cbe067 and friends, and have QEMU
> > > > > > detect
> > > > > > legacy guest? Supposedly only config space write access needs to be
> > > > > > guarded before setting FEATURES_OK.
> > > > >
> > > > > I agree. My understanding is that all vDPA must be modern device
> > > > > (since
> > > > > VIRITO_F_ACCESS_PLATFORM is mandated) instead of transitional device.
> > > > >
> > > > > Thanks
> > > > Well mlx5 has some code to handle legacy guests ...
> > > > Eli, could you comment? Is that support unused right now?
> > > >
> > > If you mean support for version 1.0, well the knob is there but it's not
> > > set in the firmware I use. Note sure if we will support this.
> > Hmm you mean it's legacy only right now?
> > Well at some point you will want advanced goodies like RSS
> > and all that is gated on 1.0 ;)
>
>
> So if my understanding is correct the device/firmware is legacy but require
> VIRTIO_F_ACCESS_PLATFORM semanic? Looks like a spec violation?
>
I am checking this with some folks here.
> Thanks
>
>
> >
> > > > > > -Siwie
> > > > > >
> > > > > > > > > > > > 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 <[email protected]>
> > > > > > > > > > > > ---
> > > > > > > > > > > > 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)
>
