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Re: [Xen-users] forcing HVM to specific network model with PV-aware FreeBSD DomU

On Thu, 2015-10-15 at 12:31 +0200, Andreas Pflug wrote:
> Hi!
> For quite a while, I've been running several pfSense firewall DomUs up
> to version 2.15 on Xen. Since the FreeBSD kernel 8.3 of pfSense wasn't
> xen-aware the model e1000 was used, and I had all networking features as
> expected though performance was degraded.
> When the new pfSense 2.2 was introduced, the kernel changed to FreeBSD
> 10.1 which now (finally!) includes a xen netfront driver, promising a
> vastly improved performance. Unfortunately, its implementation is quite
> sketchy:
> - offloading issues, which can be worked around by disabling tx
> offloading using a custom vif-script
> - VLANs are not supported. Can be achieved with multiple bridges in
> Dom0, if 8 are enough. If you need more, you're out of luck.
> - ALTQ not supported. No known workaround, preventing any traffic
> shaping.
> On the FreeBSD side, it is said that the xn xen netfront driver can't be
> disabled at boot time, unless a custom kernel is built (certainly not
> desirable regarding security updates), so:

"can't be disabled" also implies not being able to avoid unplugging the
emulated path I take it?

Otherwise you could just configure the emulated NIC and leave the PV one

> How can I disable xen-netback drivers for a specific HVM? It should
> respect the "model=e1000" setting (or maybe virtio?). I'm running Xen
> 4.4 on Debian.

According to 
http://xenbits.xen.org/docs/unstable/misc/xl-network-configuration.html the
choices are:

 * Emulated + PV
 * PV only

Unfortunately Emulated only is not a choice.

I think the right answer would be to request that FreeBSD implements some
way to keep the Emulated path and disable the PV path (e.g. similar Linux's
xen_emul_unplug command line parameter).

Oh, I just remembered that you can set xen_platform_pci=0 in your guest
cfg, that will turn of all PV extensions though, not just network.


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