Re: [PATCH 1/2] vdpa/mlx5: Fix mr->initialized semantics
From: Jason Wang
Date: Mon Aug 07 2023 - 23:01:06 EST
On Fri, Aug 4, 2023 at 1:58 AM Si-Wei Liu <si-wei.liu@xxxxxxxxxx> wrote:
>
>
>
> On 8/3/2023 1:03 AM, 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.
> >
> > 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@xxxxxxxxxx/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@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
> >>
> > _______________________________________________
> > Virtualization mailing list
> > Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx
> > https://lists.linuxfoundation.org/mailman/listinfo/virtualization
>