Date:   Fri, 20 Dec 2019 14:40:12 -0800
From:   Stephen Barber <smbarber@...omium.org>
To:     Alistair Delva <adelva@...gle.com>
Cc:     netdev@...r.kernel.org, stable@...r.kernel.org,
        "Michael S . Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        "David S . Miller" <davem@...emloft.net>, kernel-team@...roid.com,
        virtualization@...ts.linux-foundation.org,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net] virtio-net: Skip set_features on non-cvq devices

On Fri, Dec 20, 2019 at 1:22 PM Alistair Delva <adelva@...gle.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:

If you'd like to try using the control virtqueue, I have a WIP patch
at crrev.com/c/1968200

The downside there is that when enabling IP forwarding the guest
successfully disables LRO,
which AFAIK (please correct me if I'm wrong!) is generally safe when
using virtio-net. My iperf
tests showed a ~90% bandwidth reduction, so we'd need to force LRO
back on after enabling
IP forwarding if the control queue offload patch lands.

>
> 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.

This sounds okay to me. This does end up hitting a netdev_WARN later on though:
[    1.885957] ------------[ cut here ]------------
[    1.888398] netdevice: eth0: failed to disable LRO!
[    1.890369] WARNING: CPU: 0 PID: 163 at
/mnt/host/source/src/third_party/kernel/v5.4/net/core/dev.c:1483
dev_disable_lro+0x91/0x95
[    1.894761] CPU: 0 PID: 163 Comm: lxd Not tainted 5.4.5 #2
[    1.896698] Hardware name: ChromiumOS crosvm, BIOS 0
[    1.898387] RIP: 0010:dev_disable_lro+0x91/0x95
[    1.899877] Code: a6 4d 0f 44 f7 eb 07 49 c7 c6 af 78 60 a6 4c 89
ff e8 6a 00 00 00 48 c7 c7 dd 73 60 a6 4c 89 f6 48 89 c2 31 c0 e8 36
e2 a5 ff <0f> 0b eb 8a 53 48 83 ec 18 48 89 fb 65 48 8b 04 25 28 00 00
00 48
[    1.905701] RSP: 0018:ffffae0fc0427d78 EFLAGS: 00010246
[    1.907282] RAX: fe766977dd14fb00 RBX: 0000000000000001 RCX: ffffffffa683aa50
[    1.909391] RDX: fffffffffffffe6d RSI: 0000000000000082 RDI: ffffffffa683aa20
[    1.911503] RBP: ffff990bd3f8e050 R08: ffff0a1000000600 R09: 0000004000000000
[    1.913613] R10: 0000000000000193 R11: ffffffffa5af56a5 R12: ffffffffa6882690
[    1.915729] R13: ffff990bd3ec2248 R14: ffff990bd3f8e000 R15: ffff990bd3f8e000
[    1.918555] FS:  00007ca813fff700(0000) GS:ffff990bd4c00000(0000)
knlGS:0000000000000000
[    1.920648] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    1.922039] CR2: 00005ba0e1789990 CR3: 00000001d1716003 CR4: 00000000003606b0
[    1.923716] Call Trace:
[    1.924356]  devinet_sysctl_forward+0x15a/0x1b9
[    1.925444]  proc_sys_call_handler+0xc3/0xe0
[    1.926491]  __vfs_write+0x3d/0x19b
[    1.927351]  ? selinux_file_permission+0x8c/0x124
[    1.928482]  vfs_write+0xea/0x17f
[    1.929329]  ksys_write+0x68/0xc9
[    1.930178]  do_syscall_64+0x4a/0x5d
[    1.931063]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[    1.932272] RIP: 0033:0x5ba0e10655c0
[    1.933159] Code: 8b 7c 24 10 48 8b 74 24 18 48 8b 54 24 20 49 c7
c2 00 00 00 00 49 c7 c0 00 00 00 00 49 c7 c1 00 00 00 00 48 8b 44 24
08 0f 05 <48> 3d 01 f0 ff ff 76 20 48 c7 44 24 28 ff ff ff ff 48 c7 44
24 30
[    1.937440] RSP: 002b:000000c00041e258 EFLAGS: 00000216 ORIG_RAX:
0000000000000001
[    1.939224] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00005ba0e10655c0
[    1.940897] RDX: 0000000000000001 RSI: 000000c00041e4d8 RDI: 0000000000000018
[    1.942600] RBP: 000000c00041e2a8 R08: 0000000000000000 R09: 0000000000000000
[    1.944310] R10: 0000000000000000 R11: 0000000000000216 R12: 000000000000000c
[    1.946007] R13: 0000000000000032 R14: 00005ba0e0fa01e8 R15: 0000000000000000
[    1.947706] ---[ end trace 9ac0c921383f98c0 ]---


>
> [1] https://chromium.googlesource.com/chromiumos/platform/crosvm/
>
> Fixes: a02e8964eaf9 ("virtio-net: ethtool configurable LRO")
> Cc: stable@...r.kernel.org [4.20+]
> Cc: Michael S. Tsirkin <mst@...hat.com>
> Cc: Jason Wang <jasowang@...hat.com>
> Cc: David S. Miller <davem@...emloft.net>
> Cc: kernel-team@...roid.com
> Cc: virtualization@...ts.linux-foundation.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Alistair Delva <adelva@...gle.com>

Tested-by: Stephen Barber <smbarber@...omium.org>

> ---
>  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;
> +
>         if ((dev->features ^ features) & NETIF_F_LRO) {
>                 if (vi->xdp_queue_pairs)
>                         return -EBUSY;
> --
> 2.24.1.735.g03f4e72817-goog
>

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