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authorChristian Krinitsin <mail@krinitsin.com>2025-06-01 21:35:14 +0200
committerChristian Krinitsin <mail@krinitsin.com>2025-06-01 21:35:14 +0200
commit3e4c5a6261770bced301b5e74233e7866166ea5b (patch)
tree9379fddaba693ef8a045da06efee8529baa5f6f4 /gitlab/issues_text/target_missing/host_missing/accel_missing/2745
parente5634e2806195bee44407853c4bf8776f7abfa4f (diff)
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clean up repository
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-Qemu should send RARP for vhostuser regardless of whether virtio supports GUEST_ANNOUNCE
-Description of problem:
-When virtio reports to qemu that GUEST_ANNOUNCE is supported, qemu will not send RARP. The assumption, I think, is that guest kernel will do whatever is needed to announce the guest. The problem with this assumption is that 1) kernel won't send RARPs; 2) for IPv4 and IPv6 it will send GARPs and NAs; 3) for interfaces with no IP addresses, I think it won't send anything at all.
-
-RARPs are useful because they allow to notify regardless of IP configuration. I've [asked](https://issues.redhat.com/browse/RHEL-71919]) RHEL kernel folks to consider issuing RARPs from the guest kernel, but it won't happen overnight, and regardless, it's not a complete solution since we cannot expect all guests running a patched kernel with such feature.
-
-RARP packets are also often expected by underlying network components. For example, OVN controller has a special "activation-strategy=rarp" configuration that makes OVN wait for a RARP from destination chassis on live migration, and only then unblock traffic for the port. Since RARP is not issed by Qemu nor virtio-net, the OVN port is never unblocked (until its configuration is reset by CMS).
-
-I think what should be done from Qemu side is to send RARP for vhostuser ports regardless of whether virtio supports GUEST_ANNOUNCE. I **think** this can be achieved by removing this code:
-
-```
-    /* If guest supports GUEST_ANNOUNCE do nothing */
-    if (virtio_has_feature(dev->acked_features, VIRTIO_NET_F_GUEST_ANNOUNCE)) {
-        return 0;
-    }
-```
-Steps to reproduce:
-1. Start a VM with vhostuser* port and fresh virtio guest driver.
-2. Live migrate it.
-3. Observe that RARP is not sent from the migrated port. GARP (or NA for IPv6) is sent instead.
-Additional information:
-Some external bugs that may be relevant:
-
-- RHEL kernel request to send RARPs from virtio: https://issues.redhat.com/browse/RHEL-71919 (won't fix the issue for older unpatched kernels)
-- Request for OVN to handle GARPs and NAs: https://issues.redhat.com/browse/FDP-1042 (won't solve for unaddressed ports!)
-- An attempt to work around the issue in OpenStack Neutron OVN env by disabling activation strategy: https://issues.redhat.com/browse/OSPRH-12571 (not a great long term solution)