vale and netmap module questions

[Marko Zec]

On Tue, 4 Sep 2018 20:18:29 +0200
Vincenzo Maffione <v.maffione at gmail.com> wrote:

> Hi,
>   I don't think the panic depends on the architecture. Also, it does
> not depend on using emulated mode or not.
> We have seen this happening on x86_64 on FreeBSD 12 head.
> 
> As John-Mark says, kdloading netmap.ko is not enough. You need to
> open a netmap port corresponding
> to any network interface, e.g.
>  # pkt-gen -i eth0
> because this will trigger ifunit_ref() in the kernel (netmap tries to
> grab the interface called "eth0").
> The ifunit_ref() panics and we still need to figure out why.

After more carefully rereading jmg's original report, on amd64 I
reproduced exactly the same panic he reported on arm64, the summary
follows:

- the problem can be observed as VNET related, and can be triggered only
on kernels built with "options VIMAGE" but without "device netmap".

- netmap.ko built using make buildkernel works fine.

- netmap.ko built separately (cd sys/modules/netmap; make) panics on a
  first reference to vale interface, such as "tcpdump -ni vale1:a"

- the problem is that the separately built module is compiled without
  "options VIMAGE", and as such does not set curvnet prior to calling
  into network stack functions, therefore we have a null pointer
  dereference in ifunit_ref() and voila...

- hence, there's nothing to fix in the netmap code, and there's nothing
  to fix in the network stack either related to this particular problem,
  but rather we need a general mechanism which would prevent kldloading
  non-VNETized .ko modules into a VNETized kernel.  I have no idea how
  to approach this, besides adding bz@ to the cc: list, perhaps he
  could chime in with some thoughts?

Cheers,

Marko