Re: PCI passthru with Xen 3.0, NetBSD 5.1 dom0, Linux domU

[Julien Oster <julien%julien-oster.de@localhost>]

Hi Konrad,

On Mon, Jun 6, 2011 at 17:59, Konrad Rzeszutek Wilk
<konrad.wilk%oracle.com@localhost> wrote:

> Are the IRQs being delievered to DomU? You can check the /proc/interrupts.

Apparently, yes. They appear in /proc/interrupts and the card seems to
indeed do its job.

> Is it using MSI? I am not sure if NetBSD pciback supports MSI and if that
> is what it tries it might have choked on something (and I remember
> writting some patches for xen-pcifront to fix misbehaving backends).
> I think they went in 2.6.39

Hmm, good question. The card is certainly new enough. pcictl dump said:

   Interrupt pin: 0x01 (pin A)
   Interrupt line: 0xc2

... but that doesn't mean the device couldn't trigger MSI interrupts
anyway, maybe additionally, I guess? The next time I boot the domU
with PCI passthru, I'll take a look at exact kernel messages and poke
around a bit to see if I can find out what it uses.

In any way, I played around a bit and so far everything really seemed
to work well. At least I was able to associate to an AP at home (and
authenticate via WPA), and also make it act as one or even several APs
itself, using hostapd. Apart from at scan time, it rarely produced the
"Failed to stop TX DMA" messages and so far, I could not see any ill
effects. Wasn't a thorough test, though.

What did go wrong, however, was that "sometimes" (don't know what the
exact circumstances are, yet), dom0 would hang in a very peculiar
manner just after, or when completing a shutdown of the Linux domU.
Userspace seemed gone in the manner that any ssh session wasn't
responding in the slightest anymore, but kernel was still somehow
alive, giving replies to ICMP echoes after several *seconds*. I
currently have neither a VGA nor a serial console connected to the
machine, so I had to power cycle each time.

For now, I disabled the whole PCI passthru thing and replaced kernel
and tools with Xen 3.3 again because I don't absolutely need the card
right now. I want to use the Debian domU for other things instead, so
the dom0 crashes on domU shutdown bothered me.

It's no production environment, though, so I'd be happy to play around
some more and gather information.

> No, just wanted to make sure you are using something more modern than 2.6.37.
> You might want to backport 1d4610527bc71d3f9eea520fc51a02d54f79dcd0 or
> just use 2.6.39.

Ok, I will try that and check whether the TX messages disappear and if
I still encounter crashes on domU shutdown.

Cheers.
Julien