There is a bug when setting the RSS options in virtio_net that can break
the whole machine, getting the kernel into an infinite loop.
Running the following command in any QEMU virtual machine with virtionet
will reproduce this problem:
# ethtool -X eth0 hfunc toeplitz
This is how the problem happens:
1) ethtool_set_rxfh() calls virtnet_set_rxfh()
2) virtnet_set_rxfh() calls virtnet_commit_rss_command()
3) virtnet_commit_rss_command() populates 4 entries for the rss
scatter-gather
4) Since the command above does not have a key, then the last
scatter-gatter entry will be zeroed, since rss_key_size == 0.
sg_buf_size = vi->rss_key_size;
5) This buffer is passed to qemu, but qemu is not happy with a buffer
with zero length, and do the following in virtqueue_map_desc() (QEMU
function):
if (!sz) {
virtio_error(vdev, "virtio: zero sized buffers are not allowed");
6) virtio_error() (also QEMU function) set the device as broken
vdev->broken = true;
7) Qemu bails out, and do not repond this crazy kernel.
8) The kernel is waiting for the response to come back (function
virtnet_send_command())
9) The kernel is waiting doing the following :
while (!virtqueue_get_buf(vi->cvq, &tmp) &&
!virtqueue_is_broken(vi->cvq))
cpu_relax();
10) None of the following functions above is true, thus, the kernel
loops here forever. Keeping in mind that virtqueue_is_broken() does
not look at the qemu `vdev->broken`, so, it never realizes that the
vitio is broken at QEMU side.
Fix it by not sending RSS commands if the feature is not available in
the device.
Fixes: c7114b1249fa ("drivers/net/virtio_net: Added basic RSS support.")
Cc: stable@xxxxxxxxxxxxxxx
Cc: qemu-devel@xxxxxxxxxx
Signed-off-by: Breno Leitao <leitao@xxxxxxxxxx>
---
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 c640fdf28fc5..e6b0eaf08ac2 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -3809,6 +3809,9 @@ static int virtnet_set_rxfh(struct net_device *dev,
struct virtnet_info *vi = netdev_priv(dev);
int i;
+ if (!vi->has_rss && !vi->has_rss_hash_report)
+ return -EOPNOTSUPP;
+
if (rxfh->hfunc != ETH_RSS_HASH_NO_CHANGE &&
rxfh->hfunc != ETH_RSS_HASH_TOP)
return -EOPNOTSUPP;
--
2.43.0
