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

[Maxime Coquelin <maxime.coquelin@redhat.com>]

On 01/12/2018 11:13 AM, Zheng Xiang wrote:
> 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 <mst@redhat.com>
> Signed-off-by: Zheng Xiang <zhengxiang9@huawei.com>
> ---
>   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,
> 

Thanks, it fixes the silent corruption that happens with vhost-user net
backend and Windows guests, when the number of queues pairs declared in
Qemu is higher than the number of vcpus.

Tested-by: Maxime Coquelin <maxime.coquelin@redhat.com>

Maxime