netdev - [PATCH 3/3] mlx5_vdpa: defer clear_virtqueues to until DRIVER

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Date:   Sat, 6 Feb 2021 04:29:24 -0800 (PST)
From:   Si-Wei Liu <si-wei.liu@...cle.com>
To:     mst@...hat.com, jasowang@...hat.com, elic@...dia.com
Cc:     linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        si-wei.liu@...cle.com
Subject: [PATCH 3/3] mlx5_vdpa: defer clear_virtqueues to until DRIVER_OK

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().

Fixes: b35ccebe3ef7 ("vdpa/mlx5: Restore the hardware used index after change map")
Signed-off-by: Si-Wei Liu <si-wei.liu@...cle.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