Si-Wei Liu
2021-Feb-23 01:12 UTC
[PATCH] vdpa/mlx5: set_features should allow reset to zero
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 ??, 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> > >>> 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 at 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)
Jason Wang
2021-Feb-23 02:03 UTC
[PATCH] vdpa/mlx5: set_features should allow reset to zero
On 2021/2/23 9:12 ??, 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 ??, 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. > > -SiweiI think it's a bug to read config space in validate, we should move it to virtnet_probe(). 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 at 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) >