On Sun, Dec 22, 2019 at 10:54:23AM -0500, Willem de Bruijn wrote:
On Sun, Dec 22, 2019 at 9:57 AM Michael S. Tsirkin mst@redhat.com wrote:
On Sun, Dec 22, 2019 at 09:21:43AM -0500, Willem de Bruijn wrote:
On Sun, Dec 22, 2019 at 8:11 AM Michael S. Tsirkin mst@redhat.com wrote:
On Fri, Dec 20, 2019 at 10:08:41PM -0500, Willem de Bruijn wrote:
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;This would be a regression on old hypervisors which didn't have CTL VQ - suddenly they will lose offloads.
dev->features still correctly displays whether offloads are enabled. Removing it from dev->hw_features just renders it non-configurable.
Oh you are right. I confused it with dev->features.
Note that before the patch that is being fixed the offloads were enabled, but ethtool would show them as off.
So the bug is in spec, it should have said VIRTIO_NET_F_CTRL_GUEST_OFFLOADS depends on VIRTIO_NET_F_CTRL_VQ, but we missed that part. We can and I guess should add this as a recommendation but it's too late to make it a MUST.
Meanwhile I would say it's cleanest to work around this in virtnet_validate by clearing VIRTIO_NET_F_CTRL_GUEST_OFFLOADS if VIRTIO_NET_F_CTRL_VQ is off, with a big comment explaining it's a spec bug.
Wouldn't that cause precisely the regression you were concerned about?
Not sure how do you mean. VIRTIO_NET_F_CTRL_GUEST_OFFLOADS simply can't work without a ctrl vq. What's the point of keeping it on?
Workloads may now depend on LRO for cycle efficiency. Reverting to behavior before this patch (though now displaying the offload state correctly) is more conservative in that regard.
Do you see a problem with the following (untested):
Signed-off-by: Michael S. Tsirkin mst@redhat.com
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c index 4d7d5434cc5d..7b8805b47f0d 100644 --- a/drivers/net/virtio_net.c +++ b/drivers/net/virtio_net.c @@ -2971,6 +2971,15 @@ 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. Unfortunately spec forgot to + * 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,