Re: [PATCH] vdpa/mlx5: should keep avail_index despite device status

On Tue, Oct 06, 2020 at 02:22:15AM -0400, Michael S. Tsirkin wrote:

Acked-by: Eli Cohen <redacted>

On Fri, Oct 02, 2020 at 01:17:00PM -0700, Si-Wei Liu wrote:

quoted

+ Eli.

On Thu, Oct 1, 2020 at 2:02 PM Si-Wei Liu [off-list ref] wrote:

quoted

A VM with mlx5 vDPA has below warnings while being reset:

vhost VQ 0 ring restore failed: -1: Resource temporarily unavailable (11)
vhost VQ 1 ring restore failed: -1: Resource temporarily unavailable (11)

We should allow userspace emulating the virtio device be
able to get to vq's avail_index, regardless of vDPA device
status. Save the index that was last seen when virtq was
stopped, so that userspace doesn't complain.

Signed-off-by: Si-Wei Liu <redacted>

Eli can you review this pls? I need to send a pull request to Linux by
tomorrow - do we want to include this?

quoted

quoted

---
 drivers/vdpa/mlx5/net/mlx5_vnet.c | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
index 70676a6..74264e59 100644
--- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
+++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c

@@ -1133,15 +1133,17 @@ static void suspend_vq(struct mlx5_vdpa_net *ndev, struct mlx5_vdpa_virtqueue *m
        if (!mvq->initialized)
                return;

-       if (query_virtqueue(ndev, mvq, &attr)) {
-               mlx5_vdpa_warn(&ndev->mvdev, "failed to query virtqueue\n");
-               return;
-       }
        if (mvq->fw_state != MLX5_VIRTIO_NET_Q_OBJECT_STATE_RDY)
                return;

        if (modify_virtqueue(ndev, mvq, MLX5_VIRTIO_NET_Q_OBJECT_STATE_SUSPEND))
                mlx5_vdpa_warn(&ndev->mvdev, "modify to suspend failed\n");
+
+       if (query_virtqueue(ndev, mvq, &attr)) {
+               mlx5_vdpa_warn(&ndev->mvdev, "failed to query virtqueue\n");
+               return;
+       }
+       mvq->avail_idx = attr.available_index;
 }

 static void suspend_vqs(struct mlx5_vdpa_net *ndev)

@@ -1411,8 +1413,14 @@ static int mlx5_vdpa_get_vq_state(struct vdpa_device *vdev, u16 idx, struct vdpa
        struct mlx5_virtq_attr attr;
        int err;

-       if (!mvq->initialized)
-               return -EAGAIN;
+       /* If the virtq object was destroyed, use the value saved at
+        * the last minute of suspend_vq. This caters for userspace
+        * that cares about emulating the index after vq is stopped.
+        */
+       if (!mvq->initialized) {
+               state->avail_index = mvq->avail_idx;
+               return 0;
+       }

        err = query_virtqueue(ndev, mvq, &attr);
        if (err) {
--

1.8.3.1