On Tue, Sep 12, 2023 at 8:02 AM Si-Wei Liu <si-wei.liu@xxxxxxxxxx> 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@xxxxxxxxxx> 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).
> 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@xxxxxxxxxx>
> >>
> >> ---
> >> 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
> >>
>
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