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

[Dragos Tatulea]

On Tue, 2023-08-08 at 10:57 +0800, Jason Wang wrote:
> On Thu, Aug 3, 2023 at 7:40 PM Dragos Tatulea <dtatulea@xxxxxxxxxx> wrote:
> > 
> > On Thu, 2023-08-03 at 16:03 +0800, Jason Wang wrote:
> > > On Thu, Aug 3, 2023 at 1:13 AM Dragos Tatulea <dtatulea@xxxxxxxxxx> 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@xxxxxxxxxx>
> > > > Reviewed-by: Eugenio Pérez <eperezma@xxxxxxxxxx>
> > > > Reviewed-by: Gal Pressman <gal@xxxxxxxxxx>
> > > > ---
> > > >  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?
> 
> My feeling is that mr.c should be device agnostic. It needs to know
> nothing about the device details to work. But this patch seems to
> break the layer.
> 
But the same logic was there before (with the exception of cvq not having an
init flag anymore). So what am I missing here?

> > 
> > > 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.
> 
> You are right here.
> 
> Thanks
> 
> 
> > 
> > Thanks,
> > Dragos
> > 
> > > commit 6f5312f801836e6af9bcbb0bdb44dc423e129206
> > > Author: Eli Cohen <elic@xxxxxxxxxx>
> > > 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@xxxxxxxxxx>
> > >     Link: https://lore.kernel.org/r/20210602085854.62690-1-elic@xxxxxxxxxx
> > >     Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
> > >     Acked-by: Jason Wang <jasowang@xxxxxxxxxx>
> > > 
> > > 
> > 
> > > 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
> > > > 
> > > 
> > 
>