[PATCH net v2] Revert "virtio-net: ethtool configurable RXCSUM"

["Michael S. Tsirkin" <mst@redhat.com>]

This reverts commit 3618ad2a7c0e78e4258386394d5d5f92a3dbccf8.

When the device does not have a control vq (e.g. when using a
version of QEMU based on upstream v0.10 or older, or when specifying
ctrl_vq=off,ctrl_rx=off,ctrl_vlan=off,ctrl_rx_extra=off,ctrl_mac_addr=off
for the device on the QEMU command line), that commit causes a crash:

[   72.229171] kernel BUG at drivers/net/virtio_net.c:1667!
[   72.230266] invalid opcode: 0000 [#1] PREEMPT SMP
[   72.231172] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.9.0-rc8-02934-g3618ad2a7c0e7 #1
[   72.231172] EIP: virtnet_send_command+0x120/0x140
[   72.231172] Code: 00 0f 94 c0 8b 7d f0 65 33 3d 14 00 00 00 75 1c 8d 65 f4 5b 5e 5f 5d c3 66 90 be 01 00 00 00 e9 6e ff ff ff 8d b6 00
+00 00 00 <0f> 0b e8 d9 bb 82 00 eb 17 8d b4 26 00 00 00 00 8d b4 26 00 00 00
[   72.231172] EAX: 0000000d EBX: f72895c0 ECX: 00000017 EDX: 00000011
[   72.231172] ESI: f7197800 EDI: ed69bd00 EBP: ed69bcf4 ESP: ed69bc98
[   72.231172] DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068 EFLAGS: 00010246
[   72.231172] CR0: 80050033 CR2: 00000000 CR3: 02c84000 CR4: 000406f0
[   72.231172] Call Trace:
[   72.231172]  ? __virt_addr_valid+0x45/0x60
[   72.231172]  ? ___cache_free+0x51f/0x760
[   72.231172]  ? kobject_uevent_env+0xf4/0x560
[   72.231172]  virtnet_set_guest_offloads+0x4d/0x80
[   72.231172]  virtnet_set_features+0x85/0x120
[   72.231172]  ? virtnet_set_guest_offloads+0x80/0x80
[   72.231172]  __netdev_update_features+0x27a/0x8e0
[   72.231172]  ? kobject_uevent+0xa/0x20
[   72.231172]  ? netdev_register_kobject+0x12c/0x160
[   72.231172]  register_netdevice+0x4fe/0x740
[   72.231172]  register_netdev+0x1c/0x40
[   72.231172]  virtnet_probe+0x728/0xb60
[   72.231172]  ? _raw_spin_unlock+0x1d/0x40
[   72.231172]  ? virtio_vdpa_get_status+0x1c/0x20
[   72.231172]  virtio_dev_probe+0x1c6/0x271
[   72.231172]  really_probe+0x195/0x2e0
[   72.231172]  driver_probe_device+0x26/0x60
[   72.231172]  device_driver_attach+0x49/0x60
[   72.231172]  __driver_attach+0x46/0xc0
[   72.231172]  ? device_driver_attach+0x60/0x60
[   72.231172]  bus_add_driver+0x197/0x1c0
[   72.231172]  driver_register+0x66/0xc0
[   72.231172]  register_virtio_driver+0x1b/0x40
[   72.231172]  virtio_net_driver_init+0x61/0x86
[   72.231172]  ? veth_init+0x14/0x14
[   72.231172]  do_one_initcall+0x76/0x2e4
[   72.231172]  ? rdinit_setup+0x2a/0x2a
[   72.231172]  do_initcalls+0xb2/0xd5
[   72.231172]  kernel_init_freeable+0x14f/0x179
[   72.231172]  ? rest_init+0x100/0x100
[   72.231172]  kernel_init+0xd/0xe0
[   72.231172]  ret_from_fork+0x1c/0x30
[   72.231172] Modules linked in:
[   72.269563] ---[ end trace a6ebc4afea0e6cb1 ]---

The reason is that virtnet_set_features now calls virtnet_set_guest_offloads
unconditionally, it used to only call it when there is something
to configure.

If device does not have a control vq, everything breaks.

Looking at this some more, I noticed that it's not really checking the
hardware too much. E.g.

        if ((dev->features ^ features) & NETIF_F_LRO) {
                if (features & NETIF_F_LRO)
                        offloads |= GUEST_OFFLOAD_LRO_MASK &
                                    vi->guest_offloads_capable;
                else
                        offloads &= ~GUEST_OFFLOAD_LRO_MASK;
        }

and

                                (1ULL << VIRTIO_NET_F_GUEST_TSO6) | \
                                (1ULL << VIRTIO_NET_F_GUEST_ECN)  | \
                                (1ULL << VIRTIO_NET_F_GUEST_UFO))

But there's no guarantee that e.g. VIRTIO_NET_F_GUEST_TSO6 is set.

If it isn't command should not send it.

Further

static int virtnet_set_features(struct net_device *dev,
                                netdev_features_t features)
{
        struct virtnet_info *vi = netdev_priv(dev);
        u64 offloads = vi->guest_offloads;

seems wrong since guest_offloads is zero initialized,
it does not reflect the state after reset which comes from
the features.

Revert the original commit for now.

Cc: Tonghao Zhang <xiangxia.m.yue@gmail.com>
Cc: Willem de Bruijn <willemb@google.com>
Fixes: 3618ad2a7c0e7 ("virtio-net: ethtool configurable RXCSUM")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---

changes from v1:
	- clarify how to reproduce the bug in the log


 drivers/net/virtio_net.c | 50 +++++++++++-----------------------------
 1 file changed, 13 insertions(+), 37 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index d2d2c4a53cf2..21b71148c532 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -68,8 +68,6 @@ static const unsigned long guest_offloads[] = {
 				(1ULL << VIRTIO_NET_F_GUEST_ECN)  | \
 				(1ULL << VIRTIO_NET_F_GUEST_UFO))
 
-#define GUEST_OFFLOAD_CSUM_MASK (1ULL << VIRTIO_NET_F_GUEST_CSUM)
-
 struct virtnet_stat_desc {
 	char desc[ETH_GSTRING_LEN];
 	size_t offset;
@@ -2524,48 +2522,29 @@ static int virtnet_get_phys_port_name(struct net_device *dev, char *buf,
 	return 0;
 }
 
-static netdev_features_t virtnet_fix_features(struct net_device *netdev,
-					      netdev_features_t features)
-{
-	/* If Rx checksum is disabled, LRO should also be disabled. */
-	if (!(features & NETIF_F_RXCSUM))
-		features &= ~NETIF_F_LRO;
-
-	return features;
-}
-
 static int virtnet_set_features(struct net_device *dev,
 				netdev_features_t features)
 {
 	struct virtnet_info *vi = netdev_priv(dev);
-	u64 offloads = vi->guest_offloads;
+	u64 offloads;
 	int err;
 
-	/* Don't allow configuration while XDP is active. */
-	if (vi->xdp_queue_pairs)
-		return -EBUSY;
-
 	if ((dev->features ^ features) & NETIF_F_LRO) {
+		if (vi->xdp_queue_pairs)
+			return -EBUSY;
+
 		if (features & NETIF_F_LRO)
-			offloads |= GUEST_OFFLOAD_LRO_MASK &
-				    vi->guest_offloads_capable;
+			offloads = vi->guest_offloads_capable;
 		else
-			offloads &= ~GUEST_OFFLOAD_LRO_MASK;
+			offloads = vi->guest_offloads_capable &
+				   ~GUEST_OFFLOAD_LRO_MASK;
+
+		err = virtnet_set_guest_offloads(vi, offloads);
+		if (err)
+			return err;
+		vi->guest_offloads = offloads;
 	}
 
-	if ((dev->features ^ features) & NETIF_F_RXCSUM) {
-		if (features & NETIF_F_RXCSUM)
-			offloads |= GUEST_OFFLOAD_CSUM_MASK &
-				    vi->guest_offloads_capable;
-		else
-			offloads &= ~GUEST_OFFLOAD_CSUM_MASK;
-	}
-
-	err = virtnet_set_guest_offloads(vi, offloads);
-	if (err)
-		return err;
-
-	vi->guest_offloads = offloads;
 	return 0;
 }
 
@@ -2584,7 +2563,6 @@ static const struct net_device_ops virtnet_netdev = {
 	.ndo_features_check	= passthru_features_check,
 	.ndo_get_phys_port_name	= virtnet_get_phys_port_name,
 	.ndo_set_features	= virtnet_set_features,
-	.ndo_fix_features	= virtnet_fix_features,
 };
 
 static void virtnet_config_changed_work(struct work_struct *work)
@@ -3035,10 +3013,8 @@ static int virtnet_probe(struct virtio_device *vdev)
 	if (virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_TSO4) ||
 	    virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_TSO6))
 		dev->features |= NETIF_F_LRO;
-	if (virtio_has_feature(vdev, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS)) {
-		dev->hw_features |= NETIF_F_RXCSUM;
+	if (virtio_has_feature(vdev, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS))
 		dev->hw_features |= NETIF_F_LRO;
-	}
 
 	dev->vlan_features = dev->features;
 
-- 
MST