Jason Wang <[email protected]> writes: > On Thu, Oct 30, 2025 at 4:03 AM Alyssa Ross <[email protected]> wrote: >> >> Since 56a06bd40fab ("virtio_net: enable gso over UDP tunnel support."), >> networking in Cloud Hypervisor is no longer working for me. >> >> I've narrowed down the problem to here: >> >> > @@ -2555,14 +2567,21 @@ static void virtnet_receive_done(struct >> > virtnet_info *vi, struct receive_queue * >> > if (dev->features & NETIF_F_RXHASH && vi->has_rss_hash_report) >> > virtio_skb_set_hash(&hdr->hash_v1_hdr, skb); >> > >> > - if (flags & VIRTIO_NET_HDR_F_DATA_VALID) >> > - skb->ip_summed = CHECKSUM_UNNECESSARY; >> > + hdr->hdr.flags = flags; >> >> It looks like this was added because virtio_net_handle_csum_offload() >> looks at the flags from the hdr it's given, rather than having it passed >> separately, but it appears something later on relies on the previous >> value of hdr->hdr.flags. >> >> From my tracing, hdr->hdr.flags is set to either 0 or >> VIRTIO_NET_HDR_F_NEEDS_CSUM before this assignment, and flags is always >> 0, so in some cases VIRTIO_NET_HDR_F_NEEDS_CSUM now ends up being unset. > > Are you using XDP, if not there should be no change. > >> >> > + if (virtio_net_handle_csum_offload(skb, &hdr->hdr, vi->rx_tnl_csum)) >> > { >> > + net_warn_ratelimited("%s: bad csum: flags: %x, gso_type: %x >> > rx_tnl_csum %d\n", >> > + dev->name, hdr->hdr.flags, >> > + hdr->hdr.gso_type, vi->rx_tnl_csum); >> > + goto frame_err; >> > + } >> >> If I change it to save the previous value of hdr->hdr.flags, and restore >> it again here, everything works again. >> >> Disabling offload_csum in Cloud Hypervisor is a usable workaround, >> because then hdr->hdr.flags is always 0 to begin with anyway. >> >> #regzbot introduced: 56a06bd40fab > > Is mergeable rx buffer enabled, if not, I wonder if this can be fixed by: > > https://marc.info/?l=linux-netdev&m=176170721926346&w=2
That patch does fix it, thank you! #regzbot fix: virtio-net: fix incorrect flags recording in big mode
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