Re: [PATCH net] virtio-net: Skip set_features on non-cvq devices

[Willem de Bruijn <willemdebruijn.kernel@gmail.com>]

On Fri, Dec 20, 2019 at 4:22 PM Alistair Delva <adelva@google.com> wrote:
>
> On devices without control virtqueue support, such as the virtio_net
> implementation in crosvm[1], attempting to configure LRO will panic the
> kernel:
>
> kernel BUG at drivers/net/virtio_net.c:1591!
> invalid opcode: 0000 [#1] PREEMPT SMP PTI
> CPU: 1 PID: 483 Comm: Binder:330_1 Not tainted 5.4.5-01326-g19463e9acaac #1
> Hardware name: ChromiumOS crosvm, BIOS 0
> RIP: 0010:virtnet_send_command+0x15d/0x170 [virtio_net]
> Code: d8 00 00 00 80 78 02 00 0f 94 c0 65 48 8b 0c 25 28 00 00 00 48 3b 4c 24 70 75 11 48 8d 65 d8 5b 41 5c 41 5d 41 5e 41 5f 5d c3 <0f> 0b e8 ec a4 12 c8 66 90 66 2e 0f 1f 84 00 00 00 00 00 55 48 89
> RSP: 0018:ffffb97940e7bb50 EFLAGS: 00010246
> RAX: ffffffffc0596020 RBX: ffffa0e1fc8ea840 RCX: 0000000000000017
> RDX: ffffffffc0596110 RSI: 0000000000000011 RDI: 000000000000000d
> RBP: ffffb97940e7bbf8 R08: ffffa0e1fc8ea0b0 R09: ffffa0e1fc8ea0b0
> R10: ffffffffffffffff R11: ffffffffc0590940 R12: 0000000000000005
> R13: ffffa0e1ffad2c00 R14: ffffb97940e7bc08 R15: 0000000000000000
> FS:  0000000000000000(0000) GS:ffffa0e1fd100000(006b) knlGS:00000000e5ef7494
> CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
> CR2: 00000000e5eeb82c CR3: 0000000079b06001 CR4: 0000000000360ee0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> 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
>
> This happens because virtio_set_features() does not check the presence
> of the control virtqueue feature, which is sanity checked by a BUG_ON
> in virtnet_send_command().
>
> Fix this by skipping any feature processing if the control virtqueue is
> missing. This should be OK for any future feature that is added, as
> presumably all of them would require control virtqueue support to notify
> the endpoint that offload etc. should begin.
>
> [1] https://chromium.googlesource.com/chromiumos/platform/crosvm/
>
> Fixes: a02e8964eaf9 ("virtio-net: ethtool configurable LRO")
> Cc: stable@vger.kernel.org [4.20+]
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Cc: Jason Wang <jasowang@redhat.com>
> Cc: David S. Miller <davem@davemloft.net>
> Cc: kernel-team@android.com
> Cc: virtualization@lists.linux-foundation.org
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: Alistair Delva <adelva@google.com>

Thanks for debugging this, Alistair.

> ---
>  drivers/net/virtio_net.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 4d7d5434cc5d..709bcd34e485 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 (!vi->has_cvq)
> +               return 0;
> +

Instead of checking for this in virtnet_set_features, how about we
make configurability contingent on cvq in virtnet_probe:

-       if (virtio_has_feature(vdev, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS))
+       if (virtio_has_feature(vdev, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS) &&
+           virtio_has_feature(vdev, VIRTIO_NET_F_CTRL_VQ))
                dev->hw_features |= NETIF_F_LRO;

Based on this logic a little below in the same function

        if (virtio_has_feature(vdev, VIRTIO_NET_F_CTRL_VQ))
                vi->has_cvq = true;