linux-kernel - Re: [PATCH] vdpa/mlx5: Restore the hardware used index after change map

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Message-ID: <CAPWQSg0OptdAstG10e+zMvD2ZHbHdS+o2ppUxZyM0kJsd34FdA@mail.gmail.com>
Date:   Wed, 3 Feb 2021 12:33:26 -0800
From:   Si-Wei Liu <siwliu.kernel@...il.com>
To:     Eli Cohen <elic@...dia.com>, Si-Wei Liu <si-wei.liu@...cle.com>
Cc:     mst@...hat.com, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        lulu@...hat.com
Subject: Re: [PATCH] vdpa/mlx5: Restore the hardware used index after change map

On Tue, Feb 2, 2021 at 10:48 PM Eli Cohen <elic@...dia.com> wrote:
>
> On Tue, Feb 02, 2021 at 09:14:02AM -0800, Si-Wei Liu wrote:
> > On Tue, Feb 2, 2021 at 6:34 AM Eli Cohen <elic@...dia.com> wrote:
> > >
> > > When a change of memory map occurs, the hardware resources are destroyed
> > > and then re-created again with the new memory map. In such case, we need
> > > to restore the hardware available and used indices. The driver failed to
> > > restore the used index which is added here.
> > >
> > > Fixes 1a86b377aa21 ("vdpa/mlx5: Add VDPA driver for supported mlx5 devices")
> > > Signed-off-by: Eli Cohen <elic@...dia.com>
> > > ---
> > > This patch is being sent again a single patch the fixes hot memory
> > > addtion to a qemy process.
> > >
> > >  drivers/vdpa/mlx5/net/mlx5_vnet.c | 7 +++++++
> > >  1 file changed, 7 insertions(+)
> > >
> > > diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> > > index 88dde3455bfd..839f57c64a6f 100644
> > > --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
> > > +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> > > @@ -87,6 +87,7 @@ struct mlx5_vq_restore_info {
> > >         u64 device_addr;
> > >         u64 driver_addr;
> > >         u16 avail_index;
> > > +       u16 used_index;
> > >         bool ready;
> > >         struct vdpa_callback cb;
> > >         bool restore;
> > > @@ -121,6 +122,7 @@ struct mlx5_vdpa_virtqueue {
> > >         u32 virtq_id;
> > >         struct mlx5_vdpa_net *ndev;
> > >         u16 avail_idx;
> > > +       u16 used_idx;
> > >         int fw_state;
> > >
> > >         /* keep last in the struct */
> > > @@ -804,6 +806,7 @@ static int create_virtqueue(struct mlx5_vdpa_net *ndev, struct mlx5_vdpa_virtque
> > >
> > >         obj_context = MLX5_ADDR_OF(create_virtio_net_q_in, in, obj_context);
> > >         MLX5_SET(virtio_net_q_object, obj_context, hw_available_index, mvq->avail_idx);
> > > +       MLX5_SET(virtio_net_q_object, obj_context, hw_used_index, mvq->used_idx);
> >
> > The saved indexes will apply to the new virtqueue object whenever it
> > is created. In virtio spec, these indexes will reset back to zero when
> > the virtio device is reset. But I don't see how it's done today. IOW,
> > I don't see where avail_idx and used_idx get cleared from the mvq for
> > device reset via set_status().
> >
>
> Right, but this is not strictly related to this patch. I will post
> another patch to fix this.

Better to post these two patches in a series.Or else it may cause VM
reboot problem as that is where the device gets reset. The avail_index
did not as the correct value will be written to by driver right after,
but used_idx introduced by this patch is supplied by device hence this
patch alone would introduce regression.

>
> BTW, can you describe a secnario that would cause a reset (through
> calling set_status()) that happens after the VQ has been used?

You can try reboot the guest, that'll be the easy way to test.

-Siwei

>
> > -Siwei
> >
> >
> > >         MLX5_SET(virtio_net_q_object, obj_context, queue_feature_bit_mask_12_3,
> > >                  get_features_12_3(ndev->mvdev.actual_features));
> > >         vq_ctx = MLX5_ADDR_OF(virtio_net_q_object, obj_context, virtio_q_context);
> > > @@ -1022,6 +1025,7 @@ static int connect_qps(struct mlx5_vdpa_net *ndev, struct mlx5_vdpa_virtqueue *m
> > >  struct mlx5_virtq_attr {
> > >         u8 state;
> > >         u16 available_index;
> > > +       u16 used_index;
> > >  };
> > >
> > >  static int query_virtqueue(struct mlx5_vdpa_net *ndev, struct mlx5_vdpa_virtqueue *mvq,
> > > @@ -1052,6 +1056,7 @@ static int query_virtqueue(struct mlx5_vdpa_net *ndev, struct mlx5_vdpa_virtqueu
> > >         memset(attr, 0, sizeof(*attr));
> > >         attr->state = MLX5_GET(virtio_net_q_object, obj_context, state);
> > >         attr->available_index = MLX5_GET(virtio_net_q_object, obj_context, hw_available_index);
> > > +       attr->used_index = MLX5_GET(virtio_net_q_object, obj_context, hw_used_index);
> > >         kfree(out);
> > >         return 0;
> > >
> > > @@ -1610,6 +1615,7 @@ static int save_channel_info(struct mlx5_vdpa_net *ndev, struct mlx5_vdpa_virtqu
> > >                 return err;
> > >
> > >         ri->avail_index = attr.available_index;
> > > +       ri->used_index = attr.used_index;
> > >         ri->ready = mvq->ready;
> > >         ri->num_ent = mvq->num_ent;
> > >         ri->desc_addr = mvq->desc_addr;
> > > @@ -1654,6 +1660,7 @@ static void restore_channels_info(struct mlx5_vdpa_net *ndev)
> > >                         continue;
> > >
> > >                 mvq->avail_idx = ri->avail_index;
> > > +               mvq->used_idx = ri->used_index;
> > >                 mvq->ready = ri->ready;
> > >                 mvq->num_ent = ri->num_ent;
> > >                 mvq->desc_addr = ri->desc_addr;
> > > --
> > > 2.29.2
> > >