Re: [BUG] vhost-vdpa: qemu-system-s390x crashes with second virtio-net-ccw device

[Michael S. Tsirkin]

On Fri, Jul 24, 2020 at 03:27:18PM +0200, Cornelia Huck wrote:
> When I start qemu with a second virtio-net-ccw device (i.e. adding
> -device virtio-net-ccw in addition to the autogenerated device), I get
> a segfault. gdb points to
> 
> #0  0x000055d6ab52681d in virtio_net_get_config (vdev=<optimized out>, 
>     config=0x55d6ad9e3f80 "RT") at 
> /home/cohuck/git/qemu/hw/net/virtio-net.c:146
> 146       if (nc->peer->info->type == NET_CLIENT_DRIVER_VHOST_VDPA) {
> 
> (backtrace doesn't go further)
> 
> Starting qemu with no additional "-device virtio-net-ccw" (i.e., only
> the autogenerated virtio-net-ccw device is present) works. Specifying
> several "-device virtio-net-pci" works as well.
> 
> Things break with 1e0a84ea49b6 ("vhost-vdpa: introduce vhost-vdpa net
> client"), 38140cc4d971 ("vhost_net: introduce set_config & get_config")
> works (in-between state does not compile).

Ouch. I didn't test all in-between states :(
But I wish we had a 0-day instrastructure like kernel has,
that catches things like that.

> This is reproducible with tcg as well. Same problem both with
> --enable-vhost-vdpa and --disable-vhost-vdpa.
> 
> Have not yet tried to figure out what might be special with
> virtio-ccw... anyone have an idea?
> 
> [This should probably be considered a blocker?]