Re: [PATCH v2] network: add rule to nftables backend that zeroes checksum of DHCP responses

On 10/29/24 9:14 AM, Daniel P. Berrangé wrote: > On Tue, Oct 29, 2024 at 01:09:00PM +0000, Andrea Bolognani wrote: >> On Tue, Oct 29, 2024 at 12:46:55PM +0000, Daniel P. Berrangé wrote: >>> A key difference that is probably relevant is that netbsd is >>> using an e1000 NIC in QEMU, while openbsd is using a virtio-net >>> NIC. At least when created by virt-manager. >>> >>> AFAIR, QEMU's magic checksum offload only happens for virtio-net, >>> so presumably our rules are incompatible with non-virtio-net NICs >>> in someway. >> >> Yes, that's it! The GNU/Hurd and Haiku guests are also using e1000, >> since virtio drivers are not available there; moreover, if I switch a >> random Linux guest from virtio-net to e1000 I can reproduce the issue >> there as well. > > Incidentally, I think this has crossed the threshold where the cure is > worse than the disease. > > We cannot ship the forthcoming libvirt release with a checksum "fix" > that breaks all usage of NICs that aren't virtio-net, as that guarantees > brokeness for all historical OS. > > If we can't quickly find a way to improve this, I think we need to > revert (or disable) the checksum zero'ing fix for this release and > spend more time investigating it. I sadly agree :-/ (although I will point out that it's not *all* non- virtio, since e1000e seems to work). I am leaving the house now, but will make a patch to either disable or the revert the "fix" when I get back in a few hours. (I would rather leave it in with a switch or something so we could continue using standard builds to test things, but that might take too long and would definitely be too complicated for a last instant push)