Date: Thu, 25 Sep 2025 18:58:12 -0600 From: John Nielsen <lists@jnielsen.net> To: net@freebsd.org, virtualization@freebsd.org Cc: np@freebsd.org Subject: Chelsio (cxgbe) VF on FreeBSD guest under KVM requires -rxcsum Message-ID: <5D2A2499-4B43-4FE6-AA5A-AD334BC4E872@jnielsen.net>
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Hi- Not sure if this is a known issue or even an issue on the FreeBSD side = but decided to ask here first. I=E2=80=99m happy to put in a bug report = if appropriate. I have a hypervisor machine running Arch Linux with KVM, Qemu and = libvirtd. The machine has a Chelsio T520-CR adapter. I recently began = passing through virtual functions of the NIC to several of the guests I = run on the hypervisor. One of the guests runs Windows 11, and the change = was seamless. Two of the guests are running FreeBSD (14.3 or so). On = each of them the VFs were readily identified and configured (using DHCP = in one case), and ping and ARP appeared to work fine. However, TCP and = UDP traffic to the guests never received a response. After some = head-scratching and troubleshooting I discovered that running = =E2=80=9Cifconfig cxlv0 -rxcsum=E2=80=9D immediately allowed traffic to = flow as expected. As workarounds go that isn=E2=80=99t terrible, but I was surprised that = the FreeBSD guests required this adjustment while the Windows one did = not. As a point of reference I have another hypervisor machine that runs = FreeBSD 14-STABLE. It also has a Chelsio T520-CR adapter. FreeBSD guests = on that machine do not require =E2=80=9C-rxcsum=E2=80=9D in order to use = the Chelsio virtual functions. Let me know if anyone can shed some light on this. I=E2=80=99m happy to = provide additional details or run further tests if needed. Thank you! -John
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