[Feature Request] Dynamically disable/enable virtio_net LRO/CSUM

[Vesnica]

Feature Request

I'm trying to bind a XDP program to eth0 in firecracker vm. like this:
ip -force link set dev eth0 xdpdrv obj bpf_xdp.o sec from-netdev

But it failed with message:
Error: virtio_net: Can't set XDP while host is implementing LRO/CSUM, disable LRO/CSUM first

ethtool produce the following message:

root@locahost:~# ethtool -k eth0
Features for eth0:
rx-checksumming: on [fixed]
tx-checksumming: on
        tx-checksum-ipv4: off [fixed]
        tx-checksum-ip-generic: on
        tx-checksum-ipv6: off [fixed]
        tx-checksum-fcoe-crc: off [fixed]
        tx-checksum-sctp: off [fixed]
scatter-gather: on
        tx-scatter-gather: on
        tx-scatter-gather-fraglist: off [fixed]
tcp-segmentation-offload: on
        tx-tcp-segmentation: on
        tx-tcp-ecn-segmentation: off [fixed]
        tx-tcp-mangleid-segmentation: off
        tx-tcp6-segmentation: off [fixed]
generic-segmentation-offload: on
generic-receive-offload: on
large-receive-offload: on [fixed]
rx-vlan-offload: off [fixed]
tx-vlan-offload: off [fixed]
ntuple-filters: off [fixed]
receive-hashing: off [fixed]
highdma: on [fixed]
rx-vlan-filter: off [fixed]
vlan-challenged: off [fixed]
tx-lockless: off [fixed]
netns-local: off [fixed]
tx-gso-robust: on [fixed]
tx-fcoe-segmentation: off [fixed]
tx-gre-segmentation: off [fixed]
tx-gre-csum-segmentation: off [fixed]
tx-ipxip4-segmentation: off [fixed]
tx-ipxip6-segmentation: off [fixed]
tx-udp_tnl-segmentation: off [fixed]
tx-udp_tnl-csum-segmentation: off [fixed]
tx-gso-partial: off [fixed]
tx-tunnel-remcsum-segmentation: off [fixed]
tx-sctp-segmentation: off [fixed]
tx-esp-segmentation: off [fixed]
tx-udp-segmentation: off [fixed]
tx-gso-list: off [fixed]
fcoe-mtu: off [fixed]
tx-nocache-copy: off
loopback: off [fixed]
rx-fcs: off [fixed]
rx-all: off [fixed]
tx-vlan-stag-hw-insert: off [fixed]
rx-vlan-stag-hw-parse: off [fixed]
rx-vlan-stag-filter: off [fixed]
l2-fwd-offload: off [fixed]
hw-tc-offload: off [fixed]
esp-hw-offload: off [fixed]
esp-tx-csum-hw-offload: off [fixed]
rx-udp_tunnel-port-offload: off [fixed]
tls-hw-tx-offload: off [fixed]
tls-hw-rx-offload: off [fixed]
rx-gro-hw: off [fixed]
tls-hw-record: off [fixed]
rx-gro-list: off
macsec-hw-offload: off [fixed]

Because rx-checksumming and large-receive-offload are fixed，so I can't turn it off.

This prohibits the ebpf application in firecracker vm.

Describe the desired solution

Modify the net device code to make dynamically enable/disable features possible.

Checks

• [✔] Have you searched the Firecracker Issues database for similar requests?
• [✔] Have you read all the existing relevant Firecracker documentation?
• [✔] Have you read and understood Firecracker's core tenets?

[sandreim]

Hi @Vesnica. I understand that this a limitation for your usecase. We'll get back to you once we understand what are the options to enable it. Are you interested in contributing the code changes?

[Vesnica]

Unfortunately, I don’t know much about Rust or network device drivers.

The demand of this feature is not urgent at the moment, you can mark it as a low priority.

[aaglenn]

in looking to add support for veth pairs, I came across this issue and believe I've "found" the responsible code: https://github.com/firecracker-microvm/firecracker/blob/master/src/devices/src/virtio/net/device.rs#L33

this is a somewhat high priority for myself; and though I have no experience writing Rust and about 30 minutes familiarity with the firecracker codebase, I have no fear attempting to submit mergeable PR's (especially if there is anyone willing to assist/answer questions that arise)

[serban300]

Hi @aaglenn ! Indeed, that is the net device source file. The code that sets the virtio flags is here.

I was curious if you have a specific solution in mind. Modifying the flags or exposing them as API parameters should be easy. But the question is whether we can do this in a generic way. Exposing specific virtio flags through the API doesn't look like a feasible solution.

[chenhengqi]

For purpose of attaching a XDP object to network device, xdpgeneric mode would work.

[historyliao]

@chenhengqi But xdpgeneric is a test mode with poor performance.

[cperciva]

I believe this is actually two bugs in one:

1. Firecracker doesn't implement resetting virtio devices ([Feature Request] support for resetting virtio devices #3074).
2. Firecracker ignores guests disabling virtio-net features ([Bug] virtio-net: Guest can't NACK LRO #3905).

"Dynamically disabling virtio_net features" really means "reset the device and negotiate a new feature set", but neither part of that works.

[jeromegn]

I've forked and added some flags to the virtio device, yet the features are not enabled when looking at them via ethtool -k. Commenting here instead of creating a new issue because it sounds related...

I was attempting to add tx ipv6 checksum:

        let mut avail_features = 1 << VIRTIO_NET_F_GUEST_CSUM
            | 1 << VIRTIO_NET_F_CSUM
            | 1 << VIRTIO_NET_F_GUEST_TSO4
            | 1 << VIRTIO_NET_F_GUEST_TSO6
            | 1 << VIRTIO_NET_F_GUEST_UFO
            | 1 << VIRTIO_NET_F_HOST_TSO4
            | 1 << VIRTIO_NET_F_HOST_TSO6
            | 1 << VIRTIO_NET_F_HOST_UFO
            | 1 << VIRTIO_F_VERSION_1;

[ShadowCurse]

Hi all, sorry for the delay, unfortunately we were not able to make progress regarding this issue.
We are still tracking the problem and will provide an update once we will have more data to share.

[roypat]

Hey all,
as @cperciva points out, this really is a combination of two feature requests: Resetting virtio devices, and being able to NACK virtio features. We've since implemented the latter of these in #4680 (see also #3905), leaving us with only reset functionality missing. We're tracking that in #3074 though, so I'll go ahead and close this issue to avoid duplicated issues. Thanks!