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Date:   Thu, 4 Feb 2021 09:19:15 +0200
From:   Eli Cohen <elic@nvidia.com>
To:     Si-Wei Liu <siwliu.kernel@gmail.com>
CC:     Si-Wei Liu <si-wei.liu@oracle.com>, <mst@redhat.com>,
        <virtualization@lists.linux-foundation.org>,
        <netdev@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
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Subject: Re: [PATCH] vdpa/mlx5: Restore the hardware used index after change
 map
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On Wed, Feb 03, 2021 at 12:33:26PM -0800, Si-Wei Liu wrote:
> On Tue, Feb 2, 2021 at 10:48 PM Eli Cohen <elic@nvidia.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@nvidia.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@nvidia.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.
> 

Thinking it over, I think this should be all fixed in a single patch.
This fix alone introduces a regerssion as you pointed and there's no
point in fixing it in another patch.

> >
> > 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
> > > >