virtio_queue_host_notifier_read() tends to read pending event
left behind on ioeventfd in the vhost_net_stop() path, and
attempts to handle outstanding kicks from userspace vq handler.
However, in the ctrl_vq handler, virtio_net_handle_mq() has a
recursive call into virtio_net_set_status(), which may lead to
segmentation fault as shown in below stack trace:
0 0x000055f800df1780 in qdev_get_parent_bus (dev=0x0) at ../hw/core/qdev.c:376
1 0x000055f800c68ad8 in virtio_bus_device_iommu_enabled (vdev=vdev@entry=0x0)
at ../hw/virtio/virtio-bus.c:331
2 0x000055f800d70d7f in vhost_memory_unmap (dev=<optimized out>) at
../hw/virtio/vhost.c:318
3 0x000055f800d70d7f in vhost_memory_unmap (dev=<optimized out>,
buffer=0x7fc19bec5240, len=2052, is_write=1, access_len=2052) at
../hw/virtio/vhost.c:336
4 0x000055f800d71867 in vhost_virtqueue_stop (dev=dev@entry=0x55f8037ccc30,
vdev=vdev@entry=0x55f8044ec590, vq=0x55f8037cceb0, idx=0) at
../hw/virtio/vhost.c:1241
5 0x000055f800d7406c in vhost_dev_stop (hdev=hdev@entry=0x55f8037ccc30,
vdev=vdev@entry=0x55f8044ec590) at ../hw/virtio/vhost.c:1839
6 0x000055f800bf00a7 in vhost_net_stop_one (net=0x55f8037ccc30,
dev=0x55f8044ec590) at ../hw/net/vhost_net.c:315
7 0x000055f800bf0678 in vhost_net_stop (dev=dev@entry=0x55f8044ec590,
ncs=0x55f80452bae0, data_queue_pairs=data_queue_pairs@entry=7, cvq=cvq@entry=1)
at ../hw/net/vhost_net.c:423
8 0x000055f800d4e628 in virtio_net_set_status (status=<optimized out>,
n=0x55f8044ec590) at ../hw/net/virtio-net.c:296
9 0x000055f800d4e628 in virtio_net_set_status (vdev=vdev@entry=0x55f8044ec590,
status=15 '\017') at ../hw/net/virtio-net.c:370
10 0x000055f800d534d8 in virtio_net_handle_ctrl (iov_cnt=<optimized out>,
iov=<optimized out>, cmd=0 '\000', n=0x55f8044ec590) at
../hw/net/virtio-net.c:1408
11 0x000055f800d534d8 in virtio_net_handle_ctrl (vdev=0x55f8044ec590,
vq=0x7fc1a7e888d0) at ../hw/net/virtio-net.c:1452
12 0x000055f800d69f37 in virtio_queue_host_notifier_read (vq=0x7fc1a7e888d0) at
../hw/virtio/virtio.c:2331
13 0x000055f800d69f37 in virtio_queue_host_notifier_read
(n=n@entry=0x7fc1a7e8894c) at ../hw/virtio/virtio.c:3575
14 0x000055f800c688e6 in virtio_bus_cleanup_host_notifier (bus=<optimized out>,
n=n@entry=14) at ../hw/virtio/virtio-bus.c:312
15 0x000055f800d73106 in vhost_dev_disable_notifiers
(hdev=hdev@entry=0x55f8035b51b0, vdev=vdev@entry=0x55f8044ec590)
at ../../../include/hw/virtio/virtio-bus.h:35
16 0x000055f800bf00b2 in vhost_net_stop_one (net=0x55f8035b51b0,
dev=0x55f8044ec590) at ../hw/net/vhost_net.c:316
17 0x000055f800bf0678 in vhost_net_stop (dev=dev@entry=0x55f8044ec590,
ncs=0x55f80452bae0, data_queue_pairs=data_queue_pairs@entry=7, cvq=cvq@entry=1)
at ../hw/net/vhost_net.c:423
18 0x000055f800d4e628 in virtio_net_set_status (status=<optimized out>,
n=0x55f8044ec590) at ../hw/net/virtio-net.c:296
19 0x000055f800d4e628 in virtio_net_set_status (vdev=0x55f8044ec590, status=15
'\017') at ../hw/net/virtio-net.c:370
20 0x000055f800d6c4b2 in virtio_set_status (vdev=0x55f8044ec590, val=<optimized
out>) at ../hw/virtio/virtio.c:1945
21 0x000055f800d11d9d in vm_state_notify (running=running@entry=false,
state=state@entry=RUN_STATE_SHUTDOWN) at ../softmmu/runstate.c:333
22 0x000055f800d04e7a in do_vm_stop (state=state@entry=RUN_STATE_SHUTDOWN,
send_stop=send_stop@entry=false) at ../softmmu/cpus.c:262
23 0x000055f800d04e99 in vm_shutdown () at ../softmmu/cpus.c:280
24 0x000055f800d126af in qemu_cleanup () at ../softmmu/runstate.c:812
25 0x000055f800ad5b13 in main (argc=<optimized out>, argv=<optimized out>,
envp=<optimized out>) at ../softmmu/main.c:51
For now, temporarily disable handling MQ request from the ctrl_vq
userspace hanlder to avoid the recursive virtio_net_set_status()
call. Some rework is needed to allow changing the number of
queues without going through a full virtio_net_set_status cycle,
particularly for vhost-vdpa backend.
This patch will need to be reverted as soon as future patches of
having the change of #queues handled in userspace is merged.
Fixes: 402378407db ("vhost-vdpa: multiqueue support")
Signed-off-by: Si-Wei Liu <si-wei....@oracle.com>
---
hw/net/virtio-net.c | 13 +++++++++++++
1 file changed, 13 insertions(+)
diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index f0bb29c..e263116 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -1381,6 +1381,7 @@ static int virtio_net_handle_mq(VirtIONet *n, uint8_t cmd,
{
VirtIODevice *vdev = VIRTIO_DEVICE(n);
uint16_t queue_pairs;
+ NetClientState *nc = qemu_get_queue(n->nic);
virtio_net_disable_rss(n);
if (cmd == VIRTIO_NET_CTRL_MQ_HASH_CONFIG) {
@@ -1412,6 +1413,18 @@ static int virtio_net_handle_mq(VirtIONet *n, uint8_t
cmd,
return VIRTIO_NET_ERR;
}
+ /* Avoid changing the number of queue_pairs for vdpa device in
+ * userspace handler. A future fix is needed to handle the mq
+ * change in userspace handler with vhost-vdpa. Let's disable
+ * the mq handling from userspace for now and only allow get
+ * done through the kernel. Ripples may be seen when falling
+ * back to userspace, but without doing it qemu process would
+ * crash on a recursive entry to virtio_net_set_status().
+ */
+ if (nc->peer && nc->peer->info->type == NET_CLIENT_DRIVER_VHOST_VDPA) {
+ return VIRTIO_NET_ERR;
+ }
+
n->curr_queue_pairs = queue_pairs;
/* stop the backend before changing the number of queue_pairs to avoid
handling a
* disabled queue */
--
1.8.3.1
