Date: Wed, 27 Aug 2014 13:26:05 -0600 From: John Nielsen <lists@jnielsen.net> To: Brian Rak <brak@gameservers.com>, Bryan Venteicher <bryanv@freebsd.org> Cc: freebsd-hackers@freebsd.org Subject: Re: Bug in FreeBSD VirtIO network driver (only with pf enabled) Message-ID: <13EFC786-FFFB-479A-A65F-F33B07A78B9F@jnielsen.net> In-Reply-To: <53FE2B37.7050309@gameservers.com> References: <53FE2B37.7050309@gameservers.com>
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The virtio maintainer is bryanv (CC'ed). I have KVM+CentOS hosts available at $WORK so let me know if anyone needs help reproducing this or testing fixes. On Aug 27, 2014, at 1:02 PM, Brian Rak <brak@gameservers.com> wrote: > I have a FreeBSD 10 x64 guest installed inside a KVM instance on Linux. When pf is active, and the server is sending data it causes the Linux host to report warnings related to GSO. > > I've talked to some Linux developers, and they believe it to be a bug inside the FreeBSD VirtIO drivers. Based on what I'm seeing, I'm inclined to agree with them. > > Reproduction is mildly annoying, you need: > 1) A KVM guest setup with bridged networking, with FreeBSD running side using the VirtIO network interface. (We tested with CentOS, but the exact distribution should not matter) > 2) pf enabled (I'm using a single rule: "scrub in all") > 3) Some method of sending a bit of traffic from the guest (I use netcat) > > So, when I do this: > > # service pf start > # cat /root/test | nc vultr.com 80 > > The Linux kernel on the host will report: > > kernel: WARNING: CPU: 7 PID: 7772 at net/core/dev.c:2246 skb_warn_bad_offload+0xc3/0xd0() > kernel: igb: caps=(0x0000000640114bb3, 0x0000000000000000) len=1498 data_len=0 gso_size=1380 gso_type=5 ip_summed=0 > > If I do: > > # service pf stop > # cat /root/test | nc vultr.com 80 > > No such warning is reported. I can only reproduce this with pf enabled. The contents of the /root/test don't matter, I'm using 4k of data from /dev/urandom. The test file just needs to be bigger then the MTU of the host's network interface. > > I was able to track this down to the virtio_net_hdr being sent by the FreeBSD guest. With pf enabled, this outbound traffic has the following header: > > flags = 0 > gso_type = VIRTIO_NET_HDR_GSO_TCPV4 > hdr_len = 66 > gso_size = 1440 > csum_start = 0 > csum_offset = 0 > > But, this is not a valid configuration. With VIRTIO_NET_HDR_GSO_TCPV4 enabled, you should also be setting VIRTIO_NET_HDR_F_NEEDS_CSUM and populating the csum_start and csum_offset fields.
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