[Qemu-devel] [PATCH] vhost: fix corrupting GPA 0 when using uninitialized queues

[Zheng Xiang]

When guest driver only setup part of queues declared in QEMU, it
would corrupt guest's physical address 0 when using uninitialized
queues in vhost_virtqueue_start.

In AARCH64 virtual machines, the address of system memory starts at
0x40000000 and the address of rom starts at 0. So, when using qemu
with vhost-scsi, it will fail with below error:
qemu-kvm: Error start vhost dev
qemu-kvm: unable to start vhost-scsi: Cannot allocate memory

This patch fix this issue by skipping calling vhost_virtqueue_start
for uninitialized queues.

Cc: Michael S. Tsirkin <address@hidden>
Signed-off-by: Zheng Xiang <address@hidden>
---
 hw/virtio/vhost.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index e4290ce..ac79ffd 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -1532,6 +1532,8 @@ int vhost_dev_start(struct vhost_dev *hdev, VirtIODevice 
*vdev)
         goto fail_mem;
     }
     for (i = 0; i < hdev->nvqs; ++i) {
+        if (virtio_queue_get_desc_addr(vdev, hdev->vq_index + i) == 0) 
+            continue;
         r = vhost_virtqueue_start(hdev,
                                   vdev,
                                   hdev->vqs + i,
-- 
1.8.3.1