vdpa/mlx5: Fix mlx5_vdpa_get_config() endianness on big-endian machines

BugLink: https://bugs.launchpad.net/bugs/2115678

[ Upstream commit 439252e167ac45a5d46f573aac1da7d8f3e051ad ]

mlx5_vdpa_dev_add() doesn’t initialize mvdev->actual_features. It’s
initialized later by mlx5_vdpa_set_driver_features(). However,
mlx5_vdpa_get_config() depends on the VIRTIO_F_VERSION_1 flag in
actual_features, to return data with correct endianness. When it’s called
before mlx5_vdpa_set_driver_features(), the data are incorrectly returned
as big-endian on big-endian machines, while QEMU then interprets them as
little-endian.

The fix is to initialize this VIRTIO_F_VERSION_1 as early as possible,
especially considering that mlx5_vdpa_dev_add() insists on this flag to
always be set anyway.

Signed-off-by: Konstantin Shkolnyy <kshk@linux.ibm.com>
Message-Id: <20250204173127.166673-1-kshk@linux.ibm.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Dragos Tatulea <dtatulea@nvidia.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Manuel Diewald <manuel.diewald@canonical.com>
Signed-off-by: Mehmet Basaran <mehmet.basaran@canonical.com>

Author: Konstantin Shkolnyy

drivers/vdpa/mlx5/net/mlx5_vnet.c

@@ -3884,6 +3884,9 @@ static int mlx5_vdpa_dev_add(struct vdpa_mgmt_dev *v_mdev, const char *name,
 	ndev->mvdev.max_vqs = max_vqs;
 	mvdev = &ndev->mvdev;
 	mvdev->mdev = mdev;
+	/* cpu_to_mlx5vdpa16() below depends on this flag */
+	mvdev->actual_features =
+			(device_features & BIT_ULL(VIRTIO_F_VERSION_1));
 
 	ndev->vqs = kcalloc(max_vqs, sizeof(*ndev->vqs), GFP_KERNEL);
 	ndev->event_cbs = kcalloc(max_vqs + 1, sizeof(*ndev->event_cbs), GFP_KERNEL);