Messages in this thread | | | Subject | Re: [PATCH] vdpa/mlx5: set_features should allow reset to zero | From | Jason Wang <> | Date | Wed, 24 Feb 2021 14:55:13 +0800 |
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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?
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 <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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