1 files changed, 34 insertions, 0 deletions

diff --git a/gitlab/issues/target_missing/host_missing/accel_missing/2745.toml b/gitlab/issues/target_missing/host_missing/accel_missing/2745.toml
new file mode 100644
index 00000000..81a1b5e1
--- /dev/null
+++ b/gitlab/issues/target_missing/host_missing/accel_missing/2745.toml
@@ -0,0 +1,34 @@
+id = 2745
+title = "Qemu should send RARP for vhostuser regardless of whether virtio supports GUEST_ANNOUNCE"
+state = "opened"
+created_at = "2024-12-23T16:32:49.159Z"
+closed_at = "n/a"
+labels = ["Networking", "device:virtio"]
+url = "https://gitlab.com/qemu-project/qemu/-/issues/2745"
+host-os = "RHEL"
+host-arch = "any"
+qemu-version = "- QEMU command line:"
+guest-os = "- OS/kernel version:"
+guest-arch = "## Description of problem"
+description = """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;
+    }
+```"""
+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 = """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)"""