Re: [PATCH v2] virtio_console: Introduce an ID allocator for virtual console numbers

[Cédric Le Goater]

On 11/22/22 12:12, Thomas Huth wrote:
> On 14/11/2022 18.38, Cédric Le Goater wrote:
> > When a virtio console port is initialized, it is registered as an hvc
> > console using a virtual console number. If a KVM guest is started with
> > multiple virtio console devices, the same vtermno (or virtual console
> > number) can be used to allocate different hvc consoles, which leads to
> > various communication problems later on.
> >
> > This is also reported in debugfs :
> >
> >    # grep vtermno /sys/kernel/debug/virtio-ports/*
> >    /sys/kernel/debug/virtio-ports/vport1p1:console_vtermno: 1
> >    /sys/kernel/debug/virtio-ports/vport2p1:console_vtermno: 1
> >    /sys/kernel/debug/virtio-ports/vport3p1:console_vtermno: 2
> >    /sys/kernel/debug/virtio-ports/vport4p1:console_vtermno: 3
> >
> > Replace the next_vtermno global with an ID allocator and start the
> > allocation at 1 as it is today. Also recycle IDs when a console port
> > is removed.
>
> Sounds like a good idea!
>
> > @@ -1244,8 +1236,11 @@ static int init_port_console(struct port *port)
> >        * pointers.  The final argument is the output buffer size: we
> >        * can do any size, so we put PAGE_SIZE here.
> >        */
> > -    port->cons.vtermno = pdrvdata.next_vtermno;
> > +    ret = ida_alloc_range(&vtermno_ida, 1, ~0, GFP_KERNEL);
>
> Just cosmetics: I think you could use ida_alloc_min() instead.
>
> > +    if (ret < 0)
> > +        return ret;
> > +    port->cons.vtermno = ret;
> >       port->cons.hvc = hvc_alloc(port->cons.vtermno, 0, &hv_ops, PAGE_SIZE);
> >       if (IS_ERR(port->cons.hvc)) {
> >           ret = PTR_ERR(port->cons.hvc);
>
> What if this if (IS_ERR()) error happens? The code seems to return early in this case - shouldn't the ID be freed again in this case?

Oh yes. I forgot that.

Thanks,

C.