Re: [PATCH v2] virtio-net: Add check for mac address while peer is vdpa

[Jason Wang <jasowang@redhat.com>]

----- Original Message -----
> Hi jason
> 
> 
> On Mon, Oct 26, 2020 at 11:20 AM Jason Wang <jasowang@redhat.com> wrote:
> 
> >
> > On 2020/10/26 上午10:43, Jason Wang wrote:
> > >
> > > On 2020/10/23 下午5:15, Cindy Lu wrote:
> > >> Sometime vdpa get an all 0 mac address from the hardware, this will
> > >> cause the traffic down
> > >> So we add the check for this part.
> > >> if we get an 0 mac address we will use the default mac address instead
> > >>
> > >> Signed-off-by: Cindy Lu <lulu@redhat.com>
> > >> ---
> > >>   hw/net/virtio-net.c | 7 ++++++-
> > >>   1 file changed, 6 insertions(+), 1 deletion(-)
> > >>
> > >> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> > >> index 9179013ac4..f1648fc47d 100644
> > >> --- a/hw/net/virtio-net.c
> > >> +++ b/hw/net/virtio-net.c
> > >> @@ -126,6 +126,7 @@ static void virtio_net_get_config(VirtIODevice
> > >> *vdev, uint8_t *config)
> > >>       VirtIONet *n = VIRTIO_NET(vdev);
> > >>       struct virtio_net_config netcfg;
> > >>       NetClientState *nc = qemu_get_queue(n->nic);
> > >> +    static const MACAddr zero = { .a = { 0, 0, 0, 0, 0, 0 } };
> > >>         int ret = 0;
> > >>       memset(&netcfg, 0 , sizeof(struct virtio_net_config));
> > >> @@ -151,7 +152,11 @@ static void virtio_net_get_config(VirtIODevice
> > >> *vdev, uint8_t *config)
> > >>           ret = vhost_net_get_config(get_vhost_net(nc->peer),
> > >> (uint8_t *)&netcfg,
> > >>                                      n->config_size);
> > >>           if (ret != -1) {
> > >> -            memcpy(config, &netcfg, n->config_size);
> > >> +            if (memcmp(&netcfg.mac, &zero, sizeof(zero)) != 0) {
> > >> +                memcpy(config, &netcfg, n->config_size);
> > >> +        } else {
> > >> +                error_report("Get an all zero mac address from
> > >> hardware");
> > >> +            }
> > >>           }
> > >>       }
> > >>   }
> > >
> > >
> > > Applied.
> > >
> > > Thanks
> > >
> > >
> >
> > Speak too fast. Some questions:
> >
> > 1) Any reason that you do such check or get_config() instead of doing it
> > once in device initalization
> >
> get_config()  was called before the device realized.

Intersting, any reason that we need call get_config() even before
device is realized?

> If we check in the
> device initalization, the mac address is already overwritten to 0 and
> we lost the default mac address
> Also for my understanding. the mac address read from hardware should never
> been 0, so we need to check it every time we got it,

This sounds self-contradict.

> Just in case it will
> change to 0 and overwrite the mac address while the qemu running or some
> other case

This looks like a bug in the device or driver.

Even if this is true, you can only detect it via get_config(). And I
don't think we need to workaround a buggy device.

Thanks

> 
> > 2) the indentation looks wrong
> >
> sure will fix this
> 
> > 3) There's no need for an error here since we can workaround it
> 
> sure, I will change it to log
> 
> >
> >
> 
> 
> > Thanks
> >
> >
>