Messages in this thread | | | Subject | Re: [PATCH] vdpa/mlx5: set_features should allow reset to zero | From | Jason Wang <> | Date | Wed, 24 Feb 2021 11:20:01 +0800 |
| |
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
> > -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) >
| |