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Date: Thu, 3 Aug 2023 11:40:36 +0000
From: Dragos Tatulea <dtatulea@...dia.com>
To: "jasowang@...hat.com" <jasowang@...hat.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 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?
> 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@...dia.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@...dia.com>
> Link: https://lore.kernel.org/r/20210602085854.62690-1-elic@nvidia.com
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> Acked-by: Jason Wang <jasowang@...hat.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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