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From:   Jason Wang <jasowang@redhat.com>
Date:   Tue, 8 Aug 2023 11:00:00 +0800
Message-ID: <CACGkMEuAUBa=ZWi2Y48KDABsyAsQFNc4AAPmkHZyXHCQ8Vv89A@mail.gmail.com>
Subject: Re: [PATCH 1/2] vdpa/mlx5: Fix mr->initialized semantics
To:     Si-Wei Liu <si-wei.liu@oracle.com>
Cc:     Dragos Tatulea <dtatulea@nvidia.com>,
        Xuan Zhuo <xuanzhuo@linux.alibaba.com>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Gal Pressman <gal@nvidia.com>, linux-kernel@vger.kernel.org,
        virtualization@lists.linux-foundation.org,
        =?UTF-8?Q?Eugenio_P=C3=A9rez?= <eperezma@redhat.com>
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On Fri, Aug 4, 2023 at 1:58=E2=80=AFAM Si-Wei Liu <si-wei.liu@oracle.com> w=
rote:
>
>
>
> On 8/3/2023 1:03 AM, Jason Wang wrote:
> > On Thu, Aug 3, 2023 at 1:13=E2=80=AFAM 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 plac=
ed
> >> in different ASIDs, it can happen that initializing the control vq wil=
l
> >> 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 go=
t
> >> 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 P=C3=A9rez <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/co=
re/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_de=
v *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, un=
signed int asid)
> >> +{
> >> +       if (mvdev->group2asid[MLX5_VDPA_CVQ_GROUP] !=3D asid)
> >> +               return;
> >> +
> >> +       prune_iotlb(mvdev);
> >> +}
> >> +
> >> +static void _mlx5_vdpa_destroy_dvq_mr(struct mlx5_vdpa_dev *mvdev, un=
signed int asid)
> >>   {
> >>          struct mlx5_vdpa_mr *mr =3D &mvdev->mr;
> >>
> >> -       mutex_lock(&mr->mkey_mtx);
> >> +       if (mvdev->group2asid[MLX5_VDPA_DATAVQ_GROUP] !=3D 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 =3D false;
> >> -out:
> >> +}
> >> +
> >> +static void mlx5_vdpa_destroy_mr_asid(struct mlx5_vdpa_dev *mvdev, un=
signed int asid)
> >> +{
> >> +       struct mlx5_vdpa_mr *mr =3D &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 in=
t asid)
> >> +void mlx5_vdpa_destroy_mr(struct mlx5_vdpa_dev *mvdev)
> >> +{
> >> +       mlx5_vdpa_destroy_mr_asid(mvdev, mvdev->group2asid[MLX5_VDPA_C=
VQ_GROUP]);
> >> +       mlx5_vdpa_destroy_mr_asid(mvdev, mvdev->group2asid[MLX5_VDPA_D=
ATAVQ_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] !=3D 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.
> >
> > One example is that, if we only do dup_iotlb() but not try to create
> > dma mr here, we will break virtio-vdpa:
> For this case, I guess we may need another way to support virtio-vdpa
> 1:1 mapping rather than overloading virtio device reset semantics, see:
>
> https://www.mail-archive.com/qemu-devel@nongnu.org/msg953755.html
>
>  > Conceptually, the address mapping is not a part of the abstraction for
>  > a virtio device now. So resetting the memory mapping during virtio
>  > device reset seems wrong.
>
> where we want to keep memory mapping intact across virtio device reset
> for best live migration latency/downtime. I wonder would it work to
> reset the mapping in vhost-vdpa life cycle out of virtio reset, say
> introduce a .reset_map() op to restore 1:1 mapping within
> vhost_vdpa_remove_as() right after vhost_vdpa_iotlb_unmap()? Then we can
> move the iotlb reset logic to there without worry breaking virtio-vdpa.

It looks to me we don't need a new ops. We can simply do set_map()
twice or do you mean it would be faster?

Thanks

>
> Thanks,
> -Siwei
>
> >
> > 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 =3D=3D 0 while virtqueue objects =
can be
> >      created with uid =3D=3D 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 reg=
ular
> >      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 =3D &mvdev->mr;
> >>          int err;
> >>
> >> -       if (mr->initialized)
> >> +       if (mvdev->group2asid[MLX5_VDPA_DATAVQ_GROUP] !=3D asid)
> >>                  return 0;
> >>
> >> -       if (mvdev->group2asid[MLX5_VDPA_DATAVQ_GROUP] =3D=3D asid) {
> >> -               if (iotlb)
> >> -                       err =3D create_user_mr(mvdev, iotlb);
> >> -               else
> >> -                       err =3D create_dma_mr(mvdev, mr);
> >> +       if (mr->initialized)
> >> +               return 0;
> >>
> >> -               if (err)
> >> -                       return err;
> >> -       }
> >> +       if (iotlb)
> >> +               err =3D create_user_mr(mvdev, iotlb);
> >> +       else
> >> +               err =3D create_dma_mr(mvdev, mr);
> >>
> >> -       if (mvdev->group2asid[MLX5_VDPA_CVQ_GROUP] =3D=3D asid) {
> >> -               err =3D dup_iotlb(mvdev, iotlb);
> >> -               if (err)
> >> -                       goto out_err;
> >> -       }
> >> +       if (err)
> >> +               return err;
> >>
> >>          mr->initialized =3D true;
> >> +
> >> +       return 0;
> >> +}
> >> +
> >> +static int _mlx5_vdpa_create_mr(struct mlx5_vdpa_dev *mvdev,
> >> +                               struct vhost_iotlb *iotlb, unsigned in=
t asid)
> >> +{
> >> +       int err;
> >> +
> >> +       err =3D _mlx5_vdpa_create_dvq_mr(mvdev, iotlb, asid);
> >> +       if (err)
> >> +               return err;
> >> +
> >> +       err =3D _mlx5_vdpa_create_cvq_mr(mvdev, iotlb, asid);
> >> +       if (err)
> >> +               goto out_err;
> >> +
> >>          return 0;
> >>
> >>   out_err:
> >> -       if (mvdev->group2asid[MLX5_VDPA_DATAVQ_GROUP] =3D=3D 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
> >>
> > _______________________________________________
> > Virtualization mailing list
> > Virtualization@lists.linux-foundation.org
> > https://lists.linuxfoundation.org/mailman/listinfo/virtualization
>