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    SubjectRe: [PATCH 3/3] mlx5_vdpa: defer clear_virtqueues to until DRIVER_OK
    On Sat, Feb 06, 2021 at 04:29:24AM -0800, Si-Wei Liu wrote:
    > While virtq is stopped, get_vq_state() is supposed to
    > be called to get sync'ed with the latest internal
    > avail_index from device. The saved avail_index is used
    > to restate the virtq once device is started. Commit
    > b35ccebe3ef7 introduced the clear_virtqueues() routine
    > to reset the saved avail_index, however, the index
    > gets cleared a bit earlier before get_vq_state() tries
    > to read it. This would cause consistency problems when
    > virtq is restarted, e.g. through a series of link down
    > and link up events. We could defer the clearing of
    > avail_index to until the device is to be started,
    > i.e. until VIRTIO_CONFIG_S_DRIVER_OK is set again in
    > set_status().


    Not sure I understand the scenario. You are talking about reset of the
    device followed by up/down events on the interface. How can you trigger
    this?

    >
    > Fixes: b35ccebe3ef7 ("vdpa/mlx5: Restore the hardware used index after change map")
    > Signed-off-by: Si-Wei Liu <si-wei.liu@oracle.com>
    > ---
    > drivers/vdpa/mlx5/net/mlx5_vnet.c | 2 +-
    > 1 file changed, 1 insertion(+), 1 deletion(-)
    >
    > diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
    > index aa6f8cd..444ab58 100644
    > --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
    > +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
    > @@ -1785,7 +1785,6 @@ static void mlx5_vdpa_set_status(struct vdpa_device *vdev, u8 status)
    > if (!status) {
    > mlx5_vdpa_info(mvdev, "performing device reset\n");
    > teardown_driver(ndev);
    > - clear_virtqueues(ndev);
    > mlx5_vdpa_destroy_mr(&ndev->mvdev);
    > ndev->mvdev.status = 0;
    > ++mvdev->generation;
    > @@ -1794,6 +1793,7 @@ static void mlx5_vdpa_set_status(struct vdpa_device *vdev, u8 status)
    >
    > if ((status ^ ndev->mvdev.status) & VIRTIO_CONFIG_S_DRIVER_OK) {
    > if (status & VIRTIO_CONFIG_S_DRIVER_OK) {
    > + clear_virtqueues(ndev);
    > err = setup_driver(ndev);
    > if (err) {
    > mlx5_vdpa_warn(mvdev, "failed to setup driver\n");
    > --
    > 1.8.3.1
    >

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