Re: [Qemu-devel] [PATCH V2 RFT] vhost_net: don't set backend for the uninitialized virtqueue

[Jason Wang]

On 2019/3/25 下午5:56, Yuri Benditovich wrote:
> Hi Jason,
>
> This seems ok now (4 previous patches + this one)


Thanks for the testing. Could you test with just this patch? Since even 
without 4 previous patch, we've already had the check through 
virtio_queue_get_desc_addr() in vhost_virtqueue_start().


> On Mon, Mar 25, 2019 at 5:56 AM Jason Wang <address@hidden> wrote:
> > 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.
> >
> > Signed-off-by: Jason Wang <address@hidden>
> > ---
> >   hw/net/vhost_net.c | 15 +++++++++++++++
> >   1 file changed, 15 insertions(+)
> >
> > diff --git a/hw/net/vhost_net.c b/hw/net/vhost_net.c
> > index be3cc88370..04fd924d15 100644
> > --- a/hw/net/vhost_net.c
> > +++ b/hw/net/vhost_net.c
> > @@ -221,6 +221,7 @@ static int vhost_net_start_one(struct vhost_net *net,
> >                                  VirtIODevice *dev)
> >   {
> >       struct vhost_vring_file file = { };
> > +    hwaddr a;
> >       int r;
> >
> >       net->dev.nvqs = 2;
> > @@ -244,6 +245,13 @@ 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) {
> > +            a = virtio_queue_get_desc_addr(dev,
> > +                                           net->dev.vq_index +
> > +                                           file.index);
> > +            if (a == 0) {
> > +                /* Queue might not be ready for start */
> > +                continue;
> > +            }
> >               r = vhost_net_set_backend(&net->dev, &file);
> >               if (r < 0) {
> >                   r = -errno;
> > @@ -256,6 +264,13 @@ fail:
> >       file.fd = -1;
> >       if (net->nc->info->type == NET_CLIENT_DRIVER_TAP) {
> >           while (file.index-- > 0) {
> > +            a = virtio_queue_get_desc_addr(dev,
> > +                                           net->dev.vq_index +
> > +                                           file.index);
> > +            if (a == 0) {
> > +                /* Queue might not be ready for start */
> > +                continue;
> > +            }
> >               int r = vhost_net_set_backend(&net->dev, &file);
> >               assert(r >= 0);
> >           }
> > --
> > 2.19.1