Re: [PATCH RFC v3 2/4] vdpa/mlx5: implement .reset_map driver op

[Si-Wei Liu <si-wei.liu@oracle.com>]

On 9/11/2023 11:53 PM, Jason Wang wrote:
> On Tue, Sep 12, 2023 at 8:02 AM Si-Wei Liu <si-wei.liu@oracle.com> wrote:
>>
>>
>> On 9/10/2023 8:48 PM, Jason Wang wrote:
>>> On Sat, Sep 9, 2023 at 9:46 PM Si-Wei Liu <si-wei.liu@oracle.com> wrote:
>>>> Today, mlx5_vdpa gets started by preallocate 1:1 DMA mapping at
>>>> device creation time, while this 1:1 mapping will be implicitly
>>>> destroyed when the first .set_map call is invoked. Everytime
>>>> when the .reset callback is invoked, any mapping left behind will
>>>> be dropped then reset back to the initial 1:1 DMA mapping.
>>>>
>>>> In order to reduce excessive memory mapping cost during live
>>>> migration, it is desirable to decouple the vhost-vdpa iotlb
>>>> abstraction from the virtio device life cycle, i.e. mappings
>>>> should be left intact across virtio device reset. Leverage the
>>>> .reset_map callback to reset memory mapping, then the device
>>>> .reset routine can run free from having to clean up memory
>>>> mappings.
>>> It's not clear the direct relationship between the persistent mapping
>>> and reset_map.
>> Consider .reset_map as a simplified abstraction for on-chip IOMMU model,
>> decoupling memory mapping mode switching from the current vdpa_reset
>> hack. Slightly different than platform IOMMU iommu_domain_alloc/free,
>> but works the best with existing .dma_map/.set_map APIs.
> Note that iommu_domain_alloc/free doesn't imply any mappings (even the
> identity mapping).
Forget about this part, it just exposes the multi-dimension aspect of 
iommu domain unnecessarily, and I think we both don't like to. Although 
this was intended to make virtio-vdpa work seamlessly when it is used 
over mlx5-vdpa, similar to the DMA device deviation introduced to the 
vDPA driver API.

Thanks,
-Siwei
>
>> As said in the
>> other email, the distinction cannot be hidden, as there are bus drivers
>> with varied mapping needs. On the other hand, I can live with the
>> iommu_domain_alloc/free flavor strictly following the platform IOMMU
>> model, but not sure if worth the complexity.
> I'm not sure I get this, maybe you can post some RFC or pseudo code?
>
>>> Could we do it step by step? For example, remove the
>>> mlx5_vdpa_destroy_mr() in mlx5_vdpa_reset() when PERSIST_IOTLB exists?
>> I think today there's no way for the parent driver to negotiate backend
>> features with userspace, for e.g. parent won't be able to perform
>> mlx5_vdpa_destroy_mr for the virtio-vdpa case when PERSIST_IOTLB doesn't
>> exist. And this backend features stuff is a vhost specific thing, not
>> specifically tied to vdpa itself. How do we get it extended and
>> propagated up to the vdpa bus layer?
> Just to make sure we are on the same page, I just want to know what
> happens if we simply remove mlx5_vdpa_destroy_mr() in
> mlx5_vdpa_reset()?
>
>>> And then we can deal with the resetting and others on top,
>> For this proposed fix, dealing with vdpa_reset from vhost-vdpa is not
>> specifically an issue, but how to get the mapping reverted back to 1:1
>> identity/passthrough when users want to switch from vhost-vdpa to
>> virtio-vdpa is.
>>
>>>    or it needs
>>> some explanation for why reset_map() must be done first.
>> Yep, I can add more to the commit log.
> Thanks
>
>> Thanks,
>> -Siwei
>>
>>> Thanks
>>>
>>>> Signed-off-by: Si-Wei Liu <si-wei.liu@oracle.com>
>>>>
>>>> ---
>>>> RFC v1 -> v2:
>>>>     - fix error path when both CVQ and DVQ fall in same asid
>>>> ---
>>>>    drivers/vdpa/mlx5/core/mlx5_vdpa.h |  1 +
>>>>    drivers/vdpa/mlx5/core/mr.c        | 70 +++++++++++++++++++++++---------------
>>>>    drivers/vdpa/mlx5/net/mlx5_vnet.c  | 18 +++++++---
>>>>    3 files changed, 56 insertions(+), 33 deletions(-)
>>>>
>>>> diff --git a/drivers/vdpa/mlx5/core/mlx5_vdpa.h b/drivers/vdpa/mlx5/core/mlx5_vdpa.h
>>>> index b53420e..5c9a25a 100644
>>>> --- a/drivers/vdpa/mlx5/core/mlx5_vdpa.h
>>>> +++ b/drivers/vdpa/mlx5/core/mlx5_vdpa.h
>>>> @@ -123,6 +123,7 @@ int mlx5_vdpa_create_mr(struct mlx5_vdpa_dev *mvdev, struct vhost_iotlb *iotlb,
>>>>                           unsigned int asid);
>>>>    void mlx5_vdpa_destroy_mr(struct mlx5_vdpa_dev *mvdev);
>>>>    void mlx5_vdpa_destroy_mr_asid(struct mlx5_vdpa_dev *mvdev, unsigned int asid);
>>>> +int mlx5_vdpa_reset_mr(struct mlx5_vdpa_dev *mvdev, unsigned int asid);
>>>>
>>>>    #define mlx5_vdpa_warn(__dev, format, ...)                                                         \
>>>>           dev_warn((__dev)->mdev->device, "%s:%d:(pid %d) warning: " format, __func__, __LINE__,     \
>>>> diff --git a/drivers/vdpa/mlx5/core/mr.c b/drivers/vdpa/mlx5/core/mr.c
>>>> index 5a1971fc..ec2c7b4e1 100644
>>>> --- a/drivers/vdpa/mlx5/core/mr.c
>>>> +++ b/drivers/vdpa/mlx5/core/mr.c
>>>> @@ -489,21 +489,15 @@ static void destroy_user_mr(struct mlx5_vdpa_dev *mvdev, struct mlx5_vdpa_mr *mr
>>>>           }
>>>>    }
>>>>
>>>> -static void _mlx5_vdpa_destroy_cvq_mr(struct mlx5_vdpa_dev *mvdev, unsigned int asid)
>>>> +static void _mlx5_vdpa_destroy_cvq_mr(struct mlx5_vdpa_dev *mvdev)
>>>>    {
>>>> -       if (mvdev->group2asid[MLX5_VDPA_CVQ_GROUP] != asid)
>>>> -               return;
>>>> -
>>>>           prune_iotlb(mvdev);
>>>>    }
>>>>
>>>> -static void _mlx5_vdpa_destroy_dvq_mr(struct mlx5_vdpa_dev *mvdev, unsigned int asid)
>>>> +static void _mlx5_vdpa_destroy_dvq_mr(struct mlx5_vdpa_dev *mvdev)
>>>>    {
>>>>           struct mlx5_vdpa_mr *mr = &mvdev->mr;
>>>>
>>>> -       if (mvdev->group2asid[MLX5_VDPA_DATAVQ_GROUP] != asid)
>>>> -               return;
>>>> -
>>>>           if (!mr->initialized)
>>>>                   return;
>>>>
>>>> @@ -521,8 +515,10 @@ void mlx5_vdpa_destroy_mr_asid(struct mlx5_vdpa_dev *mvdev, unsigned int asid)
>>>>
>>>>           mutex_lock(&mr->mkey_mtx);
>>>>
>>>> -       _mlx5_vdpa_destroy_dvq_mr(mvdev, asid);
>>>> -       _mlx5_vdpa_destroy_cvq_mr(mvdev, asid);
>>>> +       if (mvdev->group2asid[MLX5_VDPA_DATAVQ_GROUP] == asid)
>>>> +               _mlx5_vdpa_destroy_dvq_mr(mvdev);
>>>> +       if (mvdev->group2asid[MLX5_VDPA_CVQ_GROUP] == asid)
>>>> +               _mlx5_vdpa_destroy_cvq_mr(mvdev);
>>>>
>>>>           mutex_unlock(&mr->mkey_mtx);
>>>>    }
>>>> @@ -534,25 +530,17 @@ void mlx5_vdpa_destroy_mr(struct mlx5_vdpa_dev *mvdev)
>>>>    }
>>>>
>>>>    static int _mlx5_vdpa_create_cvq_mr(struct mlx5_vdpa_dev *mvdev,
>>>> -                                   struct vhost_iotlb *iotlb,
>>>> -                                   unsigned int asid)
>>>> +                                   struct vhost_iotlb *iotlb)
>>>>    {
>>>> -       if (mvdev->group2asid[MLX5_VDPA_CVQ_GROUP] != asid)
>>>> -               return 0;
>>>> -
>>>>           return dup_iotlb(mvdev, iotlb);
>>>>    }
>>>>
>>>>    static int _mlx5_vdpa_create_dvq_mr(struct mlx5_vdpa_dev *mvdev,
>>>> -                                   struct vhost_iotlb *iotlb,
>>>> -                                   unsigned int asid)
>>>> +                                   struct vhost_iotlb *iotlb)
>>>>    {
>>>>           struct mlx5_vdpa_mr *mr = &mvdev->mr;
>>>>           int err;
>>>>
>>>> -       if (mvdev->group2asid[MLX5_VDPA_DATAVQ_GROUP] != asid)
>>>> -               return 0;
>>>> -
>>>>           if (mr->initialized)
>>>>                   return 0;
>>>>
>>>> @@ -574,18 +562,22 @@ static int _mlx5_vdpa_create_mr(struct mlx5_vdpa_dev *mvdev,
>>>>    {
>>>>           int err;
>>>>
>>>> -       err = _mlx5_vdpa_create_dvq_mr(mvdev, iotlb, asid);
>>>> -       if (err)
>>>> -               return err;
>>>> -
>>>> -       err = _mlx5_vdpa_create_cvq_mr(mvdev, iotlb, asid);
>>>> -       if (err)
>>>> -               goto out_err;
>>>> +       if (mvdev->group2asid[MLX5_VDPA_DATAVQ_GROUP] == asid) {
>>>> +               err = _mlx5_vdpa_create_dvq_mr(mvdev, iotlb);
>>>> +               if (err)
>>>> +                       return err;
>>>> +       }
>>>> +       if (mvdev->group2asid[MLX5_VDPA_CVQ_GROUP] == asid) {
>>>> +               err = _mlx5_vdpa_create_cvq_mr(mvdev, iotlb);
>>>> +               if (err)
>>>> +                       goto out_err;
>>>> +       }
>>>>
>>>>           return 0;
>>>>
>>>>    out_err:
>>>> -       _mlx5_vdpa_destroy_dvq_mr(mvdev, asid);
>>>> +       if (mvdev->group2asid[MLX5_VDPA_DATAVQ_GROUP] == asid)
>>>> +               _mlx5_vdpa_destroy_dvq_mr(mvdev);
>>>>
>>>>           return err;
>>>>    }
>>>> @@ -601,6 +593,28 @@ int mlx5_vdpa_create_mr(struct mlx5_vdpa_dev *mvdev, struct vhost_iotlb *iotlb,
>>>>           return err;
>>>>    }
>>>>
>>>> +int mlx5_vdpa_reset_mr(struct mlx5_vdpa_dev *mvdev, unsigned int asid)
>>>> +{
>>>> +       struct mlx5_vdpa_mr *mr = &mvdev->mr;
>>>> +       int err = 0;
>>>> +
>>>> +       if (asid != 0)
>>>> +               return 0;
>>>> +
>>>> +       mutex_lock(&mr->mkey_mtx);
>>>> +       if (!mr->user_mr)
>>>> +               goto out;
>>>> +       _mlx5_vdpa_destroy_dvq_mr(mvdev);
>>>> +       if (MLX5_CAP_GEN(mvdev->mdev, umem_uid_0)) {
>>>> +               err = _mlx5_vdpa_create_dvq_mr(mvdev, NULL);
>>>> +               if (err)
>>>> +                       mlx5_vdpa_warn(mvdev, "create DMA MR failed\n");
>>>> +       }
>>>> +out:
>>>> +       mutex_unlock(&mr->mkey_mtx);
>>>> +       return err;
>>>> +}
>>>> +
>>>>    int mlx5_vdpa_handle_set_map(struct mlx5_vdpa_dev *mvdev, struct vhost_iotlb *iotlb,
>>>>                                bool *change_map, unsigned int asid)
>>>>    {
>>>> diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
>>>> index 37be945..3cb5db6 100644
>>>> --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
>>>> +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
>>>> @@ -2824,7 +2824,6 @@ static int mlx5_vdpa_reset(struct vdpa_device *vdev)
>>>>           unregister_link_notifier(ndev);
>>>>           teardown_driver(ndev);
>>>>           clear_vqs_ready(ndev);
>>>> -       mlx5_vdpa_destroy_mr(&ndev->mvdev);
>>>>           ndev->mvdev.status = 0;
>>>>           ndev->mvdev.suspended = false;
>>>>           ndev->cur_num_vqs = 0;
>>>> @@ -2835,10 +2834,6 @@ static int mlx5_vdpa_reset(struct vdpa_device *vdev)
>>>>           init_group_to_asid_map(mvdev);
>>>>           ++mvdev->generation;
>>>>
>>>> -       if (MLX5_CAP_GEN(mvdev->mdev, umem_uid_0)) {
>>>> -               if (mlx5_vdpa_create_mr(mvdev, NULL, 0))
>>>> -                       mlx5_vdpa_warn(mvdev, "create MR failed\n");
>>>> -       }
>>>>           up_write(&ndev->reslock);
>>>>
>>>>           return 0;
>>>> @@ -2903,6 +2898,18 @@ static int mlx5_vdpa_set_map(struct vdpa_device *vdev, unsigned int asid,
>>>>           return err;
>>>>    }
>>>>
>>>> +static int mlx5_vdpa_reset_map(struct vdpa_device *vdev, unsigned int asid)
>>>> +{
>>>> +       struct mlx5_vdpa_dev *mvdev = to_mvdev(vdev);
>>>> +       struct mlx5_vdpa_net *ndev = to_mlx5_vdpa_ndev(mvdev);
>>>> +       int err;
>>>> +
>>>> +       down_write(&ndev->reslock);
>>>> +       err = mlx5_vdpa_reset_mr(mvdev, asid);
>>>> +       up_write(&ndev->reslock);
>>>> +       return err;
>>>> +}
>>>> +
>>>>    static struct device *mlx5_get_vq_dma_dev(struct vdpa_device *vdev, u16 idx)
>>>>    {
>>>>           struct mlx5_vdpa_dev *mvdev = to_mvdev(vdev);
>>>> @@ -3162,6 +3169,7 @@ static int mlx5_set_group_asid(struct vdpa_device *vdev, u32 group,
>>>>           .set_config = mlx5_vdpa_set_config,
>>>>           .get_generation = mlx5_vdpa_get_generation,
>>>>           .set_map = mlx5_vdpa_set_map,
>>>> +       .reset_map = mlx5_vdpa_reset_map,
>>>>           .set_group_asid = mlx5_set_group_asid,
>>>>           .get_vq_dma_dev = mlx5_get_vq_dma_dev,
>>>>           .free = mlx5_vdpa_free,
>>>> --
>>>> 1.8.3.1
>>>>

_______________________________________________
Virtualization mailing list
Virtualization@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/virtualization