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 the key scatter-gatter key if it is not set.
Fixes: c7114b1249fa ("drivers/net/virtio_net: Added basic RSS support.") Signed-off-by: Breno Leitao leitao@debian.org Cc: stable@vger.kernel.org Cc: qemu-devel@nongnu.org --- drivers/net/virtio_net.c | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-)
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c index d7ce4a1011ea..5a7700b103f8 100644 --- a/drivers/net/virtio_net.c +++ b/drivers/net/virtio_net.c @@ -3041,11 +3041,16 @@ static int virtnet_set_ringparam(struct net_device *dev, static bool virtnet_commit_rss_command(struct virtnet_info *vi) { struct net_device *dev = vi->dev; + int has_key = vi->rss_key_size; struct scatterlist sgs[4]; unsigned int sg_buf_size; + int nents = 3; + + if (has_key) + nents += 1;
/* prepare sgs */ - sg_init_table(sgs, 4); + sg_init_table(sgs, nents);
sg_buf_size = offsetof(struct virtio_net_ctrl_rss, indirection_table); sg_set_buf(&sgs[0], &vi->ctrl->rss, sg_buf_size); @@ -3057,8 +3062,13 @@ static bool virtnet_commit_rss_command(struct virtnet_info *vi) - offsetof(struct virtio_net_ctrl_rss, max_tx_vq); sg_set_buf(&sgs[2], &vi->ctrl->rss.max_tx_vq, sg_buf_size);
- sg_buf_size = vi->rss_key_size; - sg_set_buf(&sgs[3], vi->ctrl->rss.key, sg_buf_size); + if (has_key) { + /* Only populate if key is available, otherwise + * populating a buffer with zero size breaks virtio + */ + sg_buf_size = vi->rss_key_size; + sg_set_buf(&sgs[3], vi->ctrl->rss.key, sg_buf_size); + }
if (!virtnet_send_command(vi, VIRTIO_NET_CTRL_MQ, vi->has_rss ? VIRTIO_NET_CTRL_MQ_RSS_CONFIG