[Qemu-devel] vhost-net issue: does not survive reboot on ppc64

[Alexey Kardashevskiy <aik@ozlabs.ru>]

Hi!

I am having a problem with virtio-net + vhost on POWER7 machine - it does
not survive reboot of the guest.

Steps to reproduce:
1. boot the guest
2. configure eth0 and do ping - everything works
3. reboot the guest (i.e. type "reboot")
4. when it is booted, eth0 can be configured but will not work at all.

The test is:
ifconfig eth0 172.20.1.2 up
ping 172.20.1.23

If to run tcpdump on the host's "tap-id3" interface, it shows no trafic
coming from the guest. If to compare how it works before and after reboot,
I can see the guest doing an ARP request for 172.20.1.23 and receives the
response and it does the same after reboot but the answer does not come.

If to remove vhost=on, it is all good. If to try Fedora19
(v3.10-something), it all good again - works before and after reboot.


And there 2 questions:

1. does anybody have any clue what might go wrong after reboot?

2. Is there any good material to read about what exactly and how vhost
accelerates?

My understanding is that packets from the guest to the real network are
going as:
1. guest's virtio-pci-net does ioport(VIRTIO_PCI_QUEUE_NOTIFY)
2. QEMU's net/virtio-net.c calls qemu_net_queue_deliver()
3. QEMU's net/tap.c calls tap_write_packet() and this is how the host knows
that there is a new packet.


Thanks!


This how I run QEMU:
./qemu-system-ppc64 \
-enable-kvm \
-m 2048 \
-machine pseries \
-initrd 1.cpio \
-kernel vml312_virtio_net_dbg \
-nographic \
-vga none \
-netdev
tap,id=id3,ifname=tap-id3,script=ifup.sh,downscript=ifdown.sh,vhost=on \
-device virtio-net-pci,id=id4,netdev=id3,mac=C0:41:49:4b:00:00


That is bridge config:
[aik@dyn232 ~]$ brctl show
bridge name	bridge id		STP enabled	interfaces
brtest		8000.00145e992e88	no	pin	eth4


The ifup.sh script:
ifconfig $1 hw ether ee:01:02:03:04:05
/sbin/ifconfig $1 up
/usr/sbin/brctl addif brtest $1




-- 
Alexey