Paravirt domU and PCI Passthrough

[Roger Pau Monné]

On 05/11/13 09:43, Hilton Day wrote:
> Hi - firstly a warning.  While I've been running Xen on Linux for about 6
> years, I've only just started to scratch the surface of freeBSD.
> 
> I just compiled a (working) paravirt kernel for freeBSD 8.3 (actually for
> pfSense firewall), and have succeeded in running it with a couple of
> virtual interfaces.  However, I've struck a couple of limitations:
> 
> 1.  Seems to be no support for the Xen pcifront to enable pci passthrough
> to paravirt domUs?

No, there's no pcifrontend, so right now it's not possible to use i386
PV guests with pci-passthrough.

> 2.  SMP support seems to be broken - I get a kernel panic with more than
> one core for the VM.

Yes, it's broken.

> I've had a look and can't find anything like the Linux kernel option
> for CONFIG_XEN_PCIDEV_FRONTEND
> to enable pci support in paravirt? (but this could be lack of familiarity
> with freeBSD build process/tree/files).
> 
> I've succeessfully passed thorugh the same NIC to freeBSD Xen HVM domUs
> (running 8.3 and 9.1), but would prefer to get a fully paravirt instance up
> and running.
> 
> Is PCI Passthrough possible with a freeBSD paravirt domU?  I just set up a
> freeBSD 10 BETA2 environment and have kicked off the build process with:
> 
>> make buildkernel KERNCONF=XEN
> 
> I'm just wondering whether I'm chasing a dead end and should just settle
> for a XEN HVM solution?

There have been a lot of improvements recently (that apply to both HEAD
and stable-10) in order to get PVHVM working, which has a performance
similar to pure PV (or even better depending on the workload).

Also, i386 PV is currently broken on both HEAD and stable-10 AFAIK, so I
would recommend switching to PVHVM instead.

Roger.