Messages in this thread | | | Subject | Re: [PATCH] vdpa/mlx5: set_features should allow reset to zero | From | Jason Wang <> | Date | Wed, 24 Feb 2021 14:04:36 +0800 |
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On 2021/2/24 1:04 下午, Michael S. Tsirkin wrote: > On Tue, Feb 23, 2021 at 11:35:57AM -0800, 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. >> >> -Siwie > Detecting it isn't enough though, we will need a new ioctl to notify > the kernel that it's a legacy guest. Ugh :(
I'm not sure I get this, how can we know if there's a legacy driver before set_features()?
And I wonder what will hapeen if we just revert the set_features(0)?
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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