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

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Message-ID: <CACGkMEt95WsDxuc-vGWNhZfZ5G9AGUykV5+kV8oDcGZQ4jD-Lg@mail.gmail.com>
Date:   Wed, 9 Aug 2023 09:42:40 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Dragos Tatulea <dtatulea@...dia.com>
Cc:     "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "mst@...hat.com" <mst@...hat.com>,
        "eperezma@...hat.com" <eperezma@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Gal Pressman <gal@...dia.com>,
        "xuanzhuo@...ux.alibaba.com" <xuanzhuo@...ux.alibaba.com>
Subject: Re: [PATCH 1/2] vdpa/mlx5: Fix mr->initialized semantics

On Tue, Aug 8, 2023 at 3:24 PM Dragos Tatulea <dtatulea@...dia.com> wrote:
>
> On Tue, 2023-08-08 at 10:57 +0800, Jason Wang wrote:
> > On Thu, Aug 3, 2023 at 7:40 PM Dragos Tatulea <dtatulea@...dia.com> 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@...dia.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@...dia.com>
> > > > > Reviewed-by: Eugenio Pérez <eperezma@...hat.com>
> > > > > Reviewed-by: Gal Pressman <gal@...dia.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?
> >
> > 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?

Nothing, I think you're right.

I think we can have this patch go first and tweak on top by moving CVQ
aware logic into the net specific codes.

Thanks