Re: [PATCH] vhost-vdpa: Expose ASID group change after DRIVER_OK via backend feature

[Dragos Tatulea <dtatulea@nvidia.com>]

On 21.05.26 10:26, Eugenio Perez Martin wrote:
> On Mon, May 11, 2026 at 11:46 AM Dragos Tatulea <dtatulea@nvidia.com> wrote:
>>
>> The commit in the fixes tag blocked VHOST_VDPA_SET_GROUP_ASID operations
>> once DRIVER_OK is set. That is too strict for devices which can safely
>> handle this during live migration flows.
>>
>> Bring back this behavior under a new vhost backend feature flag. The
>> feature is supported by mlx5 and vdpa_sim devices.
>>
>> Fixes: 3543b04a4ea3 ("vhost: forbid change vq groups ASID if DRIVER_OK is set")
>> Signed-off-by: Dragos Tatulea <dtatulea@nvidia.com>
>> Reviewed-by: Shahar Shitrit <shshitrit@nvidia.com>
> 
> Acked-by: Eugenio Pérez <eperezma@redhat.com>
> 
>> ---
>>  drivers/vdpa/mlx5/net/mlx5_vnet.c |  3 ++-
>>  drivers/vdpa/vdpa_sim/vdpa_sim.c  |  3 ++-
>>  drivers/vhost/vdpa.c              | 13 +++++++++++--
>>  include/uapi/linux/vhost_types.h  |  4 ++++
>>  4 files changed, 19 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
>> index ad0d5fbbbca8..f89177957c76 100644
>> --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
>> +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
>> @@ -2906,7 +2906,8 @@ static void unregister_link_notifier(struct mlx5_vdpa_net *ndev)
>>
>>  static u64 mlx5_vdpa_get_backend_features(const struct vdpa_device *vdpa)
>>  {
>> -       return BIT_ULL(VHOST_BACKEND_F_ENABLE_AFTER_DRIVER_OK);
>> +       return BIT_ULL(VHOST_BACKEND_F_ENABLE_AFTER_DRIVER_OK) |
>> +              BIT_ULL(VHOST_BACKEND_F_GROUP_ASID_AFTER_DRIVER_OK);
>>  }
>>
>>  static int mlx5_vdpa_set_driver_features(struct vdpa_device *vdev, u64 features)
>> diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.c b/drivers/vdpa/vdpa_sim/vdpa_sim.c
>> index 8cb1cc2ea139..253c7fb35ea0 100644
>> --- a/drivers/vdpa/vdpa_sim/vdpa_sim.c
>> +++ b/drivers/vdpa/vdpa_sim/vdpa_sim.c
>> @@ -428,7 +428,8 @@ static u64 vdpasim_get_device_features(struct vdpa_device *vdpa)
>>
>>  static u64 vdpasim_get_backend_features(const struct vdpa_device *vdpa)
>>  {
>> -       return BIT_ULL(VHOST_BACKEND_F_ENABLE_AFTER_DRIVER_OK);
>> +       return BIT_ULL(VHOST_BACKEND_F_ENABLE_AFTER_DRIVER_OK) |
>> +              BIT_ULL(VHOST_BACKEND_F_GROUP_ASID_AFTER_DRIVER_OK);
>>  }
>>
>>  static int vdpasim_set_driver_features(struct vdpa_device *vdpa, u64 features)
>> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
>> index 692564b1bcbb..67b3f49fa709 100644
>> --- a/drivers/vhost/vdpa.c
>> +++ b/drivers/vhost/vdpa.c
>> @@ -682,7 +682,8 @@ static long vhost_vdpa_vring_ioctl(struct vhost_vdpa *v, unsigned int cmd,
>>                         return -EFAULT;
>>                 if (idx >= vdpa->ngroups || s.num >= vdpa->nas)
>>                         return -EINVAL;
>> -               if (ops->get_status(vdpa) & VIRTIO_CONFIG_S_DRIVER_OK)
>> +               if ((ops->get_status(vdpa) & VIRTIO_CONFIG_S_DRIVER_OK) &&
>> +                   !vhost_backend_has_feature(vq, VHOST_BACKEND_F_GROUP_ASID_AFTER_DRIVER_OK))
>>                         return -EBUSY;
>>                 if (!ops->set_group_asid)
>>                         return -EOPNOTSUPP;
>> @@ -791,7 +792,8 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
>>                                  BIT_ULL(VHOST_BACKEND_F_IOTLB_PERSIST) |
>>                                  BIT_ULL(VHOST_BACKEND_F_SUSPEND) |
>>                                  BIT_ULL(VHOST_BACKEND_F_RESUME) |
>> -                                BIT_ULL(VHOST_BACKEND_F_ENABLE_AFTER_DRIVER_OK)))
>> +                                BIT_ULL(VHOST_BACKEND_F_ENABLE_AFTER_DRIVER_OK) |
>> +                                BIT_ULL(VHOST_BACKEND_F_GROUP_ASID_AFTER_DRIVER_OK)))
>>                         return -EOPNOTSUPP;
>>                 if ((features & BIT_ULL(VHOST_BACKEND_F_SUSPEND)) &&
>>                      !vhost_vdpa_can_suspend(v))
>> @@ -805,6 +807,13 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
>>                 if ((features & BIT_ULL(VHOST_BACKEND_F_DESC_ASID)) &&
>>                      !vhost_vdpa_has_desc_group(v))
>>                         return -EOPNOTSUPP;
> 
> Ouch to me here. By reading the errno manual:
> 
> Nit: By reading errno(3):
> ENOTSUP - Operation not supported (POSIX.1-2001).
> EOPNOTSUPP - Operation not supported on socket (POSIX.1-2001).
> 
> I picked the wrong constant even if they share the same errno value
> (by the same page of the manual). MST, is it worth changing it?
> 
>> +               if (features & BIT_ULL(VHOST_BACKEND_F_GROUP_ASID_AFTER_DRIVER_OK)) {
>> +                       if (!(features & BIT_ULL(VHOST_BACKEND_F_IOTLB_ASID)))
>> +                               return -EINVAL;
>> +                       if (!(vhost_vdpa_get_backend_features(v) &
>> +                               BIT_ULL(VHOST_BACKEND_F_GROUP_ASID_AFTER_DRIVER_OK)))
>> +                               return -EOPNOTSUPP;
>> +               }
>>                 if ((features & BIT_ULL(VHOST_BACKEND_F_IOTLB_PERSIST)) &&
>>                      !vhost_vdpa_has_persistent_map(v))
>>                         return -EOPNOTSUPP;
>> diff --git a/include/uapi/linux/vhost_types.h b/include/uapi/linux/vhost_types.h
>> index 1c39cc5f5a31..ec1ff8a2e260 100644
>> --- a/include/uapi/linux/vhost_types.h
>> +++ b/include/uapi/linux/vhost_types.h
>> @@ -197,5 +197,9 @@ struct vhost_vdpa_iova_range {
>>  #define VHOST_BACKEND_F_DESC_ASID    0x7
>>  /* IOTLB don't flush memory mapping across device reset */
>>  #define VHOST_BACKEND_F_IOTLB_PERSIST  0x8
>> +/* Device supports changing the group ASID after DRIVER_OK.
>> + * Requires VHOST_BACKEND_F_IOTLB_ASID.
>> + */
>> +#define VHOST_BACKEND_F_GROUP_ASID_AFTER_DRIVER_OK  0x9
>>
>>  #endif
>> --
>> 2.54.0
>>
> 

Gentle ping. Is this patch missing anything?

Thanks,
Dragos