Re: [PATCH 1/2] vdpa/mlx5: Fix mr->initialized semantics

[Dragos Tatulea via Virtualization <virtualization@lists.linux-foundation.org>]

On Thu, 2023-08-03 at 16:03 +0800, Jason Wang wrote:
> On Thu, Aug 3, 2023 at 1:13 AM Dragos Tatulea <dtatulea@nvidia.com> wrote:
> > 
> > The mr->initialized flag is shared between the control vq and data vq
> > part of the mr init/uninit. But if the control vq and data vq get placed
> > in different ASIDs, it can happen that initializing the control vq will
> > prevent the data vq mr from being initialized.
> > 
> > This patch consolidates the control and data vq init parts into their
> > own init functions. The mr->initialized will now be used for the data vq
> > only. The control vq currently doesn't need a flag.
> > 
> > The uninitializing part is also taken care of: mlx5_vdpa_destroy_mr got
> > split into data and control vq functions which are now also ASID aware.
> > 
> > Fixes: 8fcd20c30704 ("vdpa/mlx5: Support different address spaces for
> > control and data")
> > Signed-off-by: Dragos Tatulea <dtatulea@nvidia.com>
> > Reviewed-by: Eugenio Pérez <eperezma@redhat.com>
> > Reviewed-by: Gal Pressman <gal@nvidia.com>
> > ---
> >  drivers/vdpa/mlx5/core/mlx5_vdpa.h |  1 +
> >  drivers/vdpa/mlx5/core/mr.c        | 97 +++++++++++++++++++++---------
> >  2 files changed, 71 insertions(+), 27 deletions(-)
> > 
> > diff --git a/drivers/vdpa/mlx5/core/mlx5_vdpa.h
> > b/drivers/vdpa/mlx5/core/mlx5_vdpa.h
> > index 25fc4120b618..a0420be5059f 100644
> > --- a/drivers/vdpa/mlx5/core/mlx5_vdpa.h
> > +++ b/drivers/vdpa/mlx5/core/mlx5_vdpa.h
> > @@ -31,6 +31,7 @@ struct mlx5_vdpa_mr {
> >         struct list_head head;
> >         unsigned long num_directs;
> >         unsigned long num_klms;
> > +       /* state of dvq mr */
> >         bool initialized;
> > 
> >         /* serialize mkey creation and destruction */
> > diff --git a/drivers/vdpa/mlx5/core/mr.c b/drivers/vdpa/mlx5/core/mr.c
> > index 03e543229791..4ae14a248a4b 100644
> > --- a/drivers/vdpa/mlx5/core/mr.c
> > +++ b/drivers/vdpa/mlx5/core/mr.c
> > @@ -489,60 +489,103 @@ static void destroy_user_mr(struct mlx5_vdpa_dev
> > *mvdev, struct mlx5_vdpa_mr *mr
> >         }
> >  }
> > 
> > -void mlx5_vdpa_destroy_mr(struct mlx5_vdpa_dev *mvdev)
> > +static void _mlx5_vdpa_destroy_cvq_mr(struct mlx5_vdpa_dev *mvdev, unsigned
> > int asid)
> > +{
> > +       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)
> >  {
> >         struct mlx5_vdpa_mr *mr = &mvdev->mr;
> > 
> > -       mutex_lock(&mr->mkey_mtx);
> > +       if (mvdev->group2asid[MLX5_VDPA_DATAVQ_GROUP] != asid)
> > +               return;
> > +
> >         if (!mr->initialized)
> > -               goto out;
> > +               return;
> > 
> > -       prune_iotlb(mvdev);
> >         if (mr->user_mr)
> >                 destroy_user_mr(mvdev, mr);
> >         else
> >                 destroy_dma_mr(mvdev, mr);
> > 
> >         mr->initialized = false;
> > -out:
> > +}
> > +
> > +static void mlx5_vdpa_destroy_mr_asid(struct mlx5_vdpa_dev *mvdev, unsigned
> > int asid)
> > +{
> > +       struct mlx5_vdpa_mr *mr = &mvdev->mr;
> > +
> > +       mutex_lock(&mr->mkey_mtx);
> > +
> > +       _mlx5_vdpa_destroy_dvq_mr(mvdev, asid);
> > +       _mlx5_vdpa_destroy_cvq_mr(mvdev, asid);
> > +
> >         mutex_unlock(&mr->mkey_mtx);
> >  }
> > 
> > -static 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)
> > +{
> > +       mlx5_vdpa_destroy_mr_asid(mvdev, mvdev-
> > >group2asid[MLX5_VDPA_CVQ_GROUP]);
> > +       mlx5_vdpa_destroy_mr_asid(mvdev, mvdev-
> > >group2asid[MLX5_VDPA_DATAVQ_GROUP]);
> > +}
> > +
> > +static int _mlx5_vdpa_create_cvq_mr(struct mlx5_vdpa_dev *mvdev,
> > +                                   struct vhost_iotlb *iotlb,
> > +                                   unsigned int asid)
> > +{
> > +       if (mvdev->group2asid[MLX5_VDPA_CVQ_GROUP] != asid)
> > +               return 0;
> > +
> > +       return dup_iotlb(mvdev, iotlb);
> 
> This worries me as conceptually, there should be no difference between
> dvq mr and cvq mr. The virtqueue should be loosely coupled with mr.
> 
Are you worried by the changes in this patch or about the possibility of having 

The reason for this change is that I noticed if you create one mr in one asid
you could be blocked out from creating another one in a different asid due to
mr->initialized being true. To me that seemed problematic. Is it not?

> One example is that, if we only do dup_iotlb() but not try to create
> dma mr here, we will break virtio-vdpa:
> 
How will that be possible? _mlx5_vdpa_create_mr calls _mlx5_vdpa_create_dvq_mr
and _mlx5_vdpa_create_cvq_mr. The only thing that is different in this patch is
that the cvq is not protected by an init flag. My understanding was that it
would be ok to dup_iotlb again. Is it not? If not I could add an additional
initialized flag for the cvq mr.

Thanks,
Dragos

> commit 6f5312f801836e6af9bcbb0bdb44dc423e129206
> Author: Eli Cohen <elic@nvidia.com>
> Date:   Wed Jun 2 11:58:54 2021 +0300
> 
>     vdpa/mlx5: Add support for running with virtio_vdpa
> 
>     In order to support running vdpa using vritio_vdpa driver, we need  to
>     create a different kind of MR, one that has 1:1 mapping, since the
>     addresses referring to virtqueues are dma addresses.
> 
>     We create the 1:1 MR in mlx5_vdpa_dev_add() only in case firmware
>     supports the general capability umem_uid_0. The reason for that is that
>     1:1 MRs must be created with uid == 0 while virtqueue objects can be
>     created with uid == 0 only when the firmware capability is on.
> 
>     If the set_map() callback is called with new translations provided
>     through iotlb, the driver will destroy the 1:1 MR and create a regular
>     one.
> 
>     Signed-off-by: Eli Cohen <elic@nvidia.com>
>     Link: https://lore.kernel.org/r/20210602085854.62690-1-elic@nvidia.com
>     Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
>     Acked-by: Jason Wang <jasowang@redhat.com>
> 
> 

> Thanks
> 
> 

> > +}
> > +
> > +static int _mlx5_vdpa_create_dvq_mr(struct mlx5_vdpa_dev *mvdev,
> > +                                   struct vhost_iotlb *iotlb,
> > +                                   unsigned int asid)
> >  {
> >         struct mlx5_vdpa_mr *mr = &mvdev->mr;
> >         int err;
> > 
> > -       if (mr->initialized)
> > +       if (mvdev->group2asid[MLX5_VDPA_DATAVQ_GROUP] != asid)
> >                 return 0;
> > 
> > -       if (mvdev->group2asid[MLX5_VDPA_DATAVQ_GROUP] == asid) {
> > -               if (iotlb)
> > -                       err = create_user_mr(mvdev, iotlb);
> > -               else
> > -                       err = create_dma_mr(mvdev, mr);
> > +       if (mr->initialized)
> > +               return 0;
> > 
> > -               if (err)
> > -                       return err;
> > -       }
> > +       if (iotlb)
> > +               err = create_user_mr(mvdev, iotlb);
> > +       else
> > +               err = create_dma_mr(mvdev, mr);
> > 
> > -       if (mvdev->group2asid[MLX5_VDPA_CVQ_GROUP] == asid) {
> > -               err = dup_iotlb(mvdev, iotlb);
> > -               if (err)
> > -                       goto out_err;
> > -       }
> > +       if (err)
> > +               return err;
> > 
> >         mr->initialized = true;
> > +
> > +       return 0;
> > +}
> > +
> > +static int _mlx5_vdpa_create_mr(struct mlx5_vdpa_dev *mvdev,
> > +                               struct vhost_iotlb *iotlb, unsigned int
> > asid)
> > +{
> > +       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;
> > +
> >         return 0;
> > 
> >  out_err:
> > -       if (mvdev->group2asid[MLX5_VDPA_DATAVQ_GROUP] == asid) {
> > -               if (iotlb)
> > -                       destroy_user_mr(mvdev, mr);
> > -               else
> > -                       destroy_dma_mr(mvdev, mr);
> > -       }
> > +       _mlx5_vdpa_destroy_dvq_mr(mvdev, asid);
> > 
> >         return err;
> >  }
> > --
> > 2.41.0
> > 
> 

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