On Mon, Dec 23, 2019 at 12:12 PM Willem de Bruijn
[off-list ref] wrote:

quoted

On Mon, Dec 23, 2019 at 2:56 PM Willem de Bruijn
[off-list ref] wrote:

quoted

00fffe0ff0 DR7: 0000000000000400

quoted

quoted

Call Trace:
 ? preempt_count_add+0x58/0xb0
 ? _raw_spin_lock_irqsave+0x36/0x70
 ? _raw_spin_unlock_irqrestore+0x1a/0x40
 ? __wake_up+0x70/0x190
 virtnet_set_features+0x90/0xf0 [virtio_net]
 __netdev_update_features+0x271/0x980
 ? nlmsg_notify+0x5b/0xa0
 dev_disable_lro+0x2b/0x190
 ? inet_netconf_notify_devconf+0xe2/0x120
 devinet_sysctl_forward+0x176/0x1e0
 proc_sys_call_handler+0x1f0/0x250
 proc_sys_write+0xf/0x20
 __vfs_write+0x3e/0x190
 ? __sb_start_write+0x6d/0xd0
 vfs_write+0xd3/0x190
 ksys_write+0x68/0xd0
 __ia32_sys_write+0x14/0x20
 do_fast_syscall_32+0x86/0xe0
 entry_SYSENTER_compat+0x7c/0x8e

A similar crash will likely trigger when enabling XDP.

Reported-by: Alistair Delva <redacted>
Reported-by: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Fixes: 3f93522ffab2 ("virtio-net: switch off offloads on demand if possible on XDP set")
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---

Lightly tested.

Alistair, could you please test and confirm that this resolves the
crash for you?

This patch doesn't work. The reason is that NETIF_F_LRO is also turned
on by TSO4/TSO6, which your patch didn't check for. So it ends up
going through the same path and crashing in the same way.

        if (virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_TSO4) ||
            virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_TSO6))
                dev->features |= NETIF_F_LRO;

It sounds like this patch is fixing something slightly differently to
my patch fixed. virtnet_set_features() doesn't care about
GUEST_OFFLOADS, it only tests against NETIF_F_LRO. Even if "offloads"
is zero, it will call virtnet_set_guest_offloads(), which triggers the
crash.

Interesting. It's surprising that it is trying to configure a flag
that is not configurable, i.e., absent from dev->hw_features
after Michael's change.

quoted

So either we need to ensure NETIF_F_LRO is never set, or

LRO might be available, just not configurable. Indeed this was what I
observed in the past.

dev_disable_lro expects that NETIF_F_LRO is always configurable. Which
I guess is a reasonable assumption, just not necessarily the case in
virtio_net.

So I think we need both patches. Correctly mark the feature as fixed
by removing from dev->hw_features and also ignore the request from
dev_disable_lro, which does not check for this.

Something like this maybe:

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 4d7d5434cc5d..0556f42b0fb5 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c

@@ -2560,6 +2560,9 @@ static int virtnet_set_features(struct net_device *dev,
        u64 offloads;
        int err;

+       if (!virtio_has_feature(vi->vdev, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS))
+               return 0;
+
        if ((dev->features ^ features) & NETIF_F_LRO) {
                if (vi->xdp_queue_pairs)
                        return -EBUSY;

@@ -2971,6 +2974,15 @@ static int virtnet_validate(struct virtio_device *vdev)
        if (!virtnet_validate_features(vdev))
                return -EINVAL;

+       /* VIRTIO_NET_F_CTRL_GUEST_OFFLOADS does not work without
+        * VIRTIO_NET_F_CTRL_VQ. However the virtio spec does not
+        * specify that VIRTIO_NET_F_CTRL_GUEST_OFFLOADS depends
+        * on VIRTIO_NET_F_CTRL_VQ so devices can set the later but
+        * not the former.
+        */
+       if (!virtio_has_feature(vdev, VIRTIO_NET_F_CTRL_VQ))
+               __virtio_clear_bit(vdev, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS);
+
        if (virtio_has_feature(vdev, VIRTIO_NET_F_MTU)) {
                int mtu = virtio_cread16(vdev,
                                         offsetof(struct virtio_net_config,