Jason Wang
2021-Feb-24 06:53 UTC
[PATCH] vdpa/mlx5: set_features should allow reset to zero
On 2021/2/24 2:46 ??, Michael S. Tsirkin wrote:> On Wed, Feb 24, 2021 at 02:04:36PM +0800, Jason Wang wrote: >> On 2021/2/24 1:04 ??, 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 ??, 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. >>>>>>> >>>>>>> -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()? > qemu knows for sure. It does not communicate this information to the > kernel right now unfortunately.I may miss something, but I still don't get how the new ioctl is supposed to work. Thanks> >> 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 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)
Michael S. Tsirkin
2021-Feb-24 07:17 UTC
[PATCH] vdpa/mlx5: set_features should allow reset to zero
On Wed, Feb 24, 2021 at 02:53:08PM +0800, Jason Wang wrote:> > On 2021/2/24 2:46 ??, Michael S. Tsirkin wrote: > > On Wed, Feb 24, 2021 at 02:04:36PM +0800, Jason Wang wrote: > > > On 2021/2/24 1:04 ??, 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 ??, 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. > > > > > > > > > > > > > > > > -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()? > > qemu knows for sure. It does not communicate this information to the > > kernel right now unfortunately. > > > I may miss something, but I still don't get how the new ioctl is supposed to > work. > > ThanksBasically on first guest access QEMU would tell kernel whether guest is using the legacy or the modern interface. E.g. virtio_pci_config_read/virtio_pci_config_write will call ioctl(ENABLE_LEGACY, 1) while virtio_pci_common_read will call ioctl(ENABLE_LEGACY, 0) Or maybe we just add GET_CONFIG_MODERN and GET_CONFIG_LEGACY and call the correct ioctl ... there are many ways to build this API.> > > > > > 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 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)