From 55e77ff717339c63b0408e0b9a1bcd313d6c0c48 Mon Sep 17 00:00:00 2001
From: Xiao Wang <jasowang@redhat.com>
Date: Fri, 24 May 2019 12:56:42 +0200
Subject: [PATCH] vhost_net: don't set backend for the uninitialized virtqueue

RH-Author: Xiao Wang <jasowang@redhat.com>
Message-id: <1558702602-3677-1-git-send-email-jasowang@redhat.com>
Patchwork-id: 88204
O-Subject: [RHEL-7.7 qemu-kvm PATCH] vhost_net: don't set backend for the uninitialized virtqueue
Bugzilla: 1608226
RH-Acked-by: Thomas Huth <thuth@redhat.com>
RH-Acked-by: Stefano Garzarella <sgarzare@redhat.com>
RH-Acked-by: Jens Freimann <jfreimann@redhat.com>

We used to set backend unconditionally, this won't work for some
guests (e.g windows driver) who may not initialize all virtqueues. For
kernel backend, this will fail since it may try to validate the rings
during setting backend.

Fixing this by simply skipping the backend set when we find desc is
not ready.

Reviewed-by: Michael S. Tsirkin<mst@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
(cherry picked from commit 23bfaf77fa801ba30bb136de7cec47728eb02f4b)
Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
---
 hw/net/vhost_net.c         | 10 ++++++++++
 hw/virtio/virtio.c         |  5 +++++
 include/hw/virtio/virtio.h |  1 +
 3 files changed, 16 insertions(+)

diff --git a/hw/net/vhost_net.c b/hw/net/vhost_net.c
index e037db6..ec22727 100644
--- a/hw/net/vhost_net.c
+++ b/hw/net/vhost_net.c
@@ -246,6 +246,11 @@ static int vhost_net_start_one(struct vhost_net *net,
         qemu_set_fd_handler(net->backend, NULL, NULL, NULL);
         file.fd = net->backend;
         for (file.index = 0; file.index < net->dev.nvqs; ++file.index) {
+            if (!virtio_queue_enabled(dev, net->dev.vq_index +
+                                      file.index)) {
+                /* Queue might not be ready for start */
+                continue;
+            }
             r = vhost_net_set_backend(&net->dev, &file);
             if (r < 0) {
                 r = -errno;
@@ -258,6 +263,11 @@ fail:
     file.fd = -1;
     if (net->nc->info->type == NET_CLIENT_DRIVER_TAP) {
         while (file.index-- > 0) {
+            if (!virtio_queue_enabled(dev, net->dev.vq_index +
+                                      file.index)) {
+                /* Queue might not be ready for start */
+                continue;
+            }
             int r = vhost_net_set_backend(&net->dev, &file);
             assert(r >= 0);
         }
diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 1c936ad..3492b20 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -2317,6 +2317,11 @@ hwaddr virtio_queue_get_desc_addr(VirtIODevice *vdev, int n)
     return vdev->vq[n].vring.desc;
 }
 
+bool virtio_queue_enabled(VirtIODevice *vdev, int n)
+{
+    return virtio_queue_get_desc_addr(vdev, n) != 0;
+}
+
 hwaddr virtio_queue_get_avail_addr(VirtIODevice *vdev, int n)
 {
     return vdev->vq[n].vring.avail;
diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
index 96313e8..3029758 100644
--- a/include/hw/virtio/virtio.h
+++ b/include/hw/virtio/virtio.h
@@ -268,6 +268,7 @@ typedef struct VirtIORNGConf VirtIORNGConf;
                       VIRTIO_F_IOMMU_PLATFORM, false)
 
 hwaddr virtio_queue_get_desc_addr(VirtIODevice *vdev, int n);
+bool virtio_queue_enabled(VirtIODevice *vdev, int n);
 hwaddr virtio_queue_get_avail_addr(VirtIODevice *vdev, int n);
 hwaddr virtio_queue_get_used_addr(VirtIODevice *vdev, int n);
 hwaddr virtio_queue_get_desc_size(VirtIODevice *vdev, int n);
-- 
1.8.3.1