From 521a1953bc11ab6823dcbbee773bcf86e926a9e7 Mon Sep 17 00:00:00 2001

From: Si-Wei Liu <si-wei.liu@oracle.com>

Date: Fri, 6 May 2022 19:28:18 -0700

Subject: [PATCH 14/16] virtio-net: don't handle mq request in userspace

 handler for vhost-vdpa

MIME-Version: 1.0

Content-Type: text/plain; charset=UTF-8

Content-Transfer-Encoding: 8bit

RH-Author: Jason Wang <jasowang@redhat.com>

RH-MergeRequest: 98: Multiqueue fixes for vhost-vDPA

RH-Commit: [7/7] 9781cab45448ae16a00fbf10cf7995df6b984a0a (jasowang/qemu-kvm-cs)

RH-Bugzilla: 2070804

RH-Acked-by: Eugenio Pérez <eperezma@redhat.com>

RH-Acked-by: Laurent Vivier <lvivier@redhat.com>

RH-Acked-by: Cindy Lu <lulu@redhat.com>

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.liu@oracle.com>

Acked-by: Jason Wang <jasowang@redhat.com>

Message-Id: <1651890498-24478-8-git-send-email-si-wei.liu@oracle.com>

Reviewed-by: Michael S. Tsirkin <mst@redhat.com>

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

(cherry picked from commit 2a7888cc3aa31faee839fa5dddad354ff8941f4c)

Signed-off-by: Jason Wang <jasowang@redhat.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 f0bb29c741..099e65036d 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 */

-- 

2.31.1