linux-kernel - [PATCH 2/3] mlx5_vdpa: fix feature negotiation across device reset

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Message-ID: <1612614564-4220-2-git-send-email-si-wei.liu@oracle.com>
Date:   Sat, 6 Feb 2021 04:29:23 -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 2/3] mlx5_vdpa: fix feature negotiation across device reset

The mlx_features denotes the capability for which
set of virtio features is supported by device. In
principle, this field needs not be cleared during
virtio device reset, as this capability is static
and does not change across reset.

In fact, the current code may have the assumption
that mlx_features can be reloaded from firmware
via the .get_features ops after device is reset
(via the .set_status ops), which is unfortunately
not true. The userspace VMM might save a copy
of backend capable features and won't call into
kernel again to get it on reset. This causes all
virtio features getting disabled on newly created
virtqs after device reset, while guest would hold
mismatched view of available features. For e.g.,
the guest may still assume tx checksum offload
is available after reset and feature negotiation,
causing frames with bogus (incomplete) checksum
transmitted on the wire.

Signed-off-by: Si-Wei Liu <si-wei.liu@...cle.com>
---
 drivers/vdpa/mlx5/net/mlx5_vnet.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
index b8416c4..aa6f8cd 100644
--- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
+++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
@@ -1788,7 +1788,6 @@ static void mlx5_vdpa_set_status(struct vdpa_device *vdev, u8 status)
 		clear_virtqueues(ndev);
 		mlx5_vdpa_destroy_mr(&ndev->mvdev);
 		ndev->mvdev.status = 0;
-		ndev->mvdev.mlx_features = 0;
 		++mvdev->generation;
 		return;
 	}
-- 
1.8.3.1