Re: [PATCH net] virtio_net: CTRL_GUEST_OFFLOADS depends on CTRL_VQ
From: Jason Wang
Date: Mon Dec 23 2019 - 21:49:44 EST
On 2019/12/24 äå4:21, Alistair Delva wrote:
On Mon, Dec 23, 2019 at 12:12 PM Willem de Bruijn
<willemdebruijn.kernel@xxxxxxxxx> wrote:
On Mon, Dec 23, 2019 at 2:56 PM Willem de Bruijn
<willemdebruijn.kernel@xxxxxxxxx> wrote:
00fffe0ff0 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
A similar crash will likely trigger when enabling XDP.
Reported-by: Alistair Delva <adelva@xxxxxxxxxx>
Reported-by: Willem de Bruijn <willemdebruijn.kernel@xxxxxxxxx>
Fixes: 3f93522ffab2 ("virtio-net: switch off offloads on demand if possible on XDP set")
Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
---
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.
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,
We check feature dependency and fail the probe in
virtnet_validate_features().
Is it more straightforward to fail the probe there when
CTRL_GUEST_OFFLOADS was set but CTRL_VQ wasn't?
Thanks