Re: [RFC] vdpa/mlx5: preserve CVQ vringh index

[Jason Wang]

On Mon, Oct 30, 2023 at 10:06 PM Steven Sistare
<steven.sistare@xxxxxxxxxx> wrote:
>
> On 10/27/2023 2:31 AM, Jason Wang wrote:
> > On Fri, Oct 27, 2023 at 4:07 AM Steve Sistare <steven.sistare@xxxxxxxxxx> wrote:
> >>
> >> mlx5_vdpa does not preserve userland's view of vring base for the control
> >> queue in the following sequence:
> >>
> >> ioctl VHOST_SET_VRING_BASE
> >> ioctl VHOST_VDPA_SET_STATUS VIRTIO_CONFIG_S_DRIVER_OK
> >>   mlx5_vdpa_set_status()
> >>     setup_cvq_vring()
> >>       vringh_init_iotlb()
> >>         vringh_init_kern()
> >>           vrh->last_avail_idx = 0;
> >> ioctl VHOST_GET_VRING_BASE
> >>
> >> To fix, restore the value of cvq->vring.last_avail_idx after calling
> >> vringh_init_iotlb.
> >>
> >> Signed-off-by: Steve Sistare <steven.sistare@xxxxxxxxxx>
> >> ---
> >>  drivers/vdpa/mlx5/net/mlx5_vnet.c |  7 ++++++-
> >>  drivers/vhost/vringh.c            | 30 ++++++++++++++++++++++++++++++
> >>  include/linux/vringh.h            |  2 ++
> >>  3 files changed, 38 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> >> index 946488b8989f..f64758143115 100644
> >> --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
> >> +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> >> @@ -2795,13 +2795,18 @@ static int setup_cvq_vring(struct mlx5_vdpa_dev *mvdev)
> >>         struct mlx5_control_vq *cvq = &mvdev->cvq;
> >>         int err = 0;
> >>
> >> -       if (mvdev->actual_features & BIT_ULL(VIRTIO_NET_F_CTRL_VQ))
> >> +       if (mvdev->actual_features & BIT_ULL(VIRTIO_NET_F_CTRL_VQ)) {
> >> +               u16 last_avail_idx = cvq->vring.last_avail_idx;
> >> +
> >>                 err = vringh_init_iotlb(&cvq->vring, mvdev->actual_features,
> >>                                         MLX5_CVQ_MAX_ENT, false,
> >>                                         (struct vring_desc *)(uintptr_t)cvq->desc_addr,
> >>                                         (struct vring_avail *)(uintptr_t)cvq->driver_addr,
> >>                                         (struct vring_used *)(uintptr_t)cvq->device_addr);
> >>
> >> +               if (!err)
> >> +                       vringh_set_base_iotlb(&cvq->vring, last_avail_idx);
> >
> > Btw, vringh_set_base_iotlb() deserves an independent patch and it
> > seems it is not specific to IOTLB,
>
> Agreed on both.  I initially submitted the smallest change needed to show the problem.
>
> so we probably need an indirection
> > to have vringh_set_base() first.
>
> Not sure what you mean.  I have defined:
>
>     static inline int __vringh_set_base() ...
>
>     int vringh_set_base_iotlb()
>         return __vringh_set_base(vrh, idx, putu16_iotlb);
>
> to which I would add:
>
>     int vringh_set_base_user()
>         return __vringh_set_base(vrh, idx, putu16_user);
>
>     int vringh_set_base_kern()
>         return __vringh_set_base(vrh, idx, putu16_kern;
>
> all in the same patch.
>
> The call site in mlx5_vnet.c would be a 2nd patch.

Right, so we just need to split it.

>
> - Steve
>
> > Or I wonder if it's better to just introduce a new parameter to
> > vringh_init_iotlb()...
>
> I considered that, but IMO the parameter list there is already large, and it would
> be strange to add a parameter for the initial value of avail, but not for used, and
> no one needs the latter.

Fine.

Thanks

>
> - Steve
>
> >> +       }
> >>         return err;
> >>  }
> >>
> >> diff --git a/drivers/vhost/vringh.c b/drivers/vhost/vringh.c
> >> index 7b8fd977f71c..799762c83007 100644
> >> --- a/drivers/vhost/vringh.c
> >> +++ b/drivers/vhost/vringh.c
> >> @@ -595,6 +595,24 @@ static inline void __vringh_notify_disable(struct vringh *vrh,
> >>         }
> >>  }
> >>
> >> +static inline int __vringh_set_base(struct vringh *vrh, u16 idx,
> >> +                           int (*putu16)(const struct vringh *vrh,
> >> +                               __virtio16 *p, u16 val))
> >> +{
> >> +    int ret;
> >> +
> >> +    ret = putu16(vrh, &vrh->vring.avail->idx, idx);
> >> +    if (ret)
> >> +        return ret;
> >> +
> >> +    ret = putu16(vrh, &vrh->vring.used->idx, idx);
> >> +    if (ret)
> >> +        return ret;
> >> +
> >> +    vrh->last_avail_idx = vrh->last_used_idx = idx;
> >> +    return 0;
> >> +}
> >> +
> >>  /* Userspace access helpers: in this case, addresses are really userspace. */
> >>  static inline int getu16_user(const struct vringh *vrh, u16 *val, const __virtio16 *p)
> >>  {
> >> @@ -1456,6 +1474,18 @@ void vringh_set_iotlb(struct vringh *vrh, struct vhost_iotlb *iotlb,
> >>  }
> >>  EXPORT_SYMBOL(vringh_set_iotlb);
> >>
> >> +/**
> >> + * vringh_set_base_iotlb - set avail_idx and used_idx
> >> + * @vrh: the vring
> >> + * @idx: the value to set
> >> + */
> >> +int vringh_set_base_iotlb(struct vringh *vrh, u16 idx)
> >> +{
> >> +    return __vringh_set_base(vrh, idx, putu16_iotlb);
> >> +}
> >> +EXPORT_SYMBOL(vringh_set_base_iotlb);
> >> +
> >> +
> >>  /**
> >>   * vringh_getdesc_iotlb - get next available descriptor from ring with
> >>   * IOTLB.
> >> diff --git a/include/linux/vringh.h b/include/linux/vringh.h
> >> index c3a8117dabe8..e9b8af4e6a5e 100644
> >> --- a/include/linux/vringh.h
> >> +++ b/include/linux/vringh.h
> >> @@ -306,6 +306,8 @@ int vringh_init_iotlb_va(struct vringh *vrh, u64 features,
> >>                          struct vring_avail *avail,
> >>                          struct vring_used *used);
> >>
> >> +int vringh_set_base_iotlb(struct vringh *vrh, u16 idx);
> >> +
> >>  int vringh_getdesc_iotlb(struct vringh *vrh,
> >>                          struct vringh_kiov *riov,
> >>                          struct vringh_kiov *wiov,
> >> --
> >> 2.39.3
> >>
> >
>