Re: [Xen-devel] PCI passthrough issue

[Jean Baptiste Favre <xen-devel@xxxxxxxxxxx>]

Le 12/01/2011 17:36, Konrad Rzeszutek Wilk a écrit :
> On Wed, Jan 12, 2011 at 04:53:51PM +0100, Jean Baptiste Favre wrote:
>> Hello Konrad,
>>
>> Le 12/01/2011 16:43, Konrad Rzeszutek Wilk a écrit :
>>> On Wed, Jan 12, 2011 at 04:38:49PM +0100, Jean Baptiste Favre wrote:
>>>> Hello,
>>>> I'm facing a strange issue with network card PCI passthrough on my
>>>> openwrt test domU.
>>>>
>>>> - With network PCI passthrough, DNS lookup failed for some domains
>>>> (exemple, google.com) but not for other (free.fr my ISP, or my domain
>>>> jbfavre.org). I can ping an IP address without any problem.
>>>
>>> Do you have "both" (so PCI passthrough and the Xen network driver)
>>> in the guest? If so, have you tried eliminating the xen network driver
>>> to see if it is just a routing issue?
>> Have not tried to eliminate xen network driver. Think I have both drivers.
>>
>> My kernel .config looks like:
>> $ grep XEN build_dir/linux-x86_xen_domu/linux-2.6.37/.config
>> CONFIG_XEN=y
>> # CONFIG_XEN_PRIVILEGED_GUEST is not set
>> CONFIG_XEN_PVHVM=y
>> CONFIG_XEN_MAX_DOMAIN_MEMORY=128
>> CONFIG_XEN_SAVE_RESTORE=y
>> CONFIG_PCI_XEN=y
>> CONFIG_XEN_PCIDEV_FRONTEND=y
>> CONFIG_XEN_BLKDEV_FRONTEND=y
>> CONFIG_XEN_NETDEV_FRONTEND=y
>> CONFIG_HVC_XEN=y
>> CONFIG_XEN_BALLOON=y
>> CONFIG_XEN_SCRUB_PAGES=y
>> CONFIG_XEN_DEV_EVTCHN=y
>> CONFIG_XENFS=y
>> CONFIG_XEN_COMPAT_XENFS=y
>> CONFIG_XEN_SYS_HYPERVISOR=y
>> # CONFIG_XEN_PLATFORM_PCI is not set
>> CONFIG_SWIOTLB_XEN=y
>>
>> So, I should remove CONFIG_XEN_NETDEV_FRONTEND ?
> 
> No. You can just do 'ifconfig <x> down' whatever your Xen netfront
> NIC is. .. but.
>>
>>> What does your routing table look like? Your IP table?
>> My routing table is pretty clean, nothing strange here
>> # route -n
>> Kernel IP routing table
>> Destination     Gateway         Genmask         Flags Metric Ref    Use
>> Iface
>> 10.0.0.0        0.0.0.0         255.255.255.0   U     0      0        0
>> br-wan
>> 0.0.0.0         10.0.0.1        0.0.0.0         UG    0      0        0
>> br-wan
> 
> Ok, then the idea that the Xen networking driver and the PCI passthrough send
> packets over is not the way..
> 
> So ignore about the Xen networking part.

OK.

>>
>>>> - Starting domU as a "normal" (ie without PCI passthrough), no problem.
>>>>
>>>>
>>>> As far as I can say, domU is not the root cause. I really think this is
>>>> related to PCI passsthrough. This seems to be related to packet length.
>>>
>>> Then that would imply the MTU is not set right. 
>> Already checked it: 1500 :)
> Ok.
> 
> Next thing, did you try to disable the rx/tx checksumming?

No. Not sure I even know how to do it, but will have a look on that.

> If you connect the Ethernet cable for this 'br-wan' device to another machine
> (so you could set it up as bridge and just let it pass through packets and 
> sniff
> the data) what do the packets look like?

I can see packets on my gateway (which acts as DNS as well). They looks
good. I can see DNS answers as well leaving the gateway, but not
reaching my domU. Have only basic switches between my gateway and my domU.

> What happens if the PCI passthrough device is not under the ownership of a 
> bridge?
> What then? You wouldn't have any bridge firewall code in?

Removed bridge + configure eth: no change.
Checked ebtables/iptables (all tables: net filter and mangle) rules:
empty, Policy to ACCEPT.
Tried to enable/disable ip_forwarding: no change
Also disabled IPV6 support (I saw some DNS answers as AAAA but no IPv6
available at home for now): no change

Regards,
JB

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