[RFC v2 12/14] virtio-net: detect RSS state mid-migration changes

[Jonah Palmer <jonah.palmer@oracle.com>]

Save the current RSS state at early migration time to compare with
later during the stop-and-copy phase.

Only the RSS state that can change mid-migration is tracked.

RSS fields derived from backend capability/feature negotiation (for
example software-RSS capability flags and supported/peer hash capability
metadata) are intentionally excluded from delta checks.

Signed-off-by: Jonah Palmer <jonah.palmer@oracle.com>
---
 hw/net/virtio-net.c            | 50 ++++++++++++++++++++++++++++++++++
 include/hw/virtio/virtio-net.h | 16 +++++++++++
 2 files changed, 66 insertions(+)

diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index 2c0b42debb..3ee49a043a 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -3943,6 +3943,27 @@ static int virtio_net_early_pre_save(void *opaque)
     vnet_mig->mq_early = n->multiqueue;
     vnet_mig->queue_pairs_early = n->curr_queue_pairs;
 
+    /* RSS state snapshot */
+    vnet_mig->rss_enabled_early = n->rss_data.enabled;
+    vnet_mig->rss_redirect_early = n->rss_data.redirect;
+    vnet_mig->rss_populate_hash_early = n->rss_data.populate_hash;
+    vnet_mig->rss_runtime_hash_types_early = n->rss_data.runtime_hash_types;
+    vnet_mig->rss_indirections_len_early = n->rss_data.indirections_len;
+    vnet_mig->rss_default_queue_early = n->rss_data.default_queue;
+    memcpy(vnet_mig->rss_key_early, n->rss_data.key, VIRTIO_NET_RSS_MAX_KEY_SIZE);
+
+    /* Snapshot RSS indirections table if present */
+    g_free(vnet_mig->rss_indirections_table_early);
+    vnet_mig->rss_indirections_table_early = NULL;
+
+    if (n->rss_data.indirections_len && n->rss_data.indirections_table) {
+        /* Casting to size_t avoids implicit narrow/widen arithmetic */
+        size_t bytes = (size_t)n->rss_data.indirections_len * sizeof(uint16_t);
+
+        vnet_mig->rss_indirections_table_early =
+            g_memdup2(n->rss_data.indirections_table, bytes);
+    }
+
     return 0;
 }
 
@@ -4233,6 +4254,8 @@ static void virtio_net_device_unrealize(DeviceState *dev)
         n->migration->mtable_macs_early = NULL;
         g_free(n->migration->vlans_early);
         n->migration->vlans_early = NULL;
+        g_free(n->migration->rss_indirections_table_early);
+        n->migration->rss_indirections_table_early = NULL;
         g_free(n->migration);
         n->migration = NULL;
 
@@ -4389,6 +4412,33 @@ static bool virtio_net_has_delta(VirtIONet *n, VirtIODevice *vdev)
         return true;
     }
 
+    /* Has the VirtIONet's RSS state changed? */
+    if (n->rss_data.enabled != vnet_mig->rss_enabled_early ||
+        n->rss_data.redirect != vnet_mig->rss_redirect_early ||
+        n->rss_data.populate_hash != vnet_mig->rss_populate_hash_early ||
+        n->rss_data.runtime_hash_types != vnet_mig->rss_runtime_hash_types_early ||
+        n->rss_data.indirections_len != vnet_mig->rss_indirections_len_early ||
+        n->rss_data.default_queue != vnet_mig->rss_default_queue_early) {
+        return true;
+    }
+    if (memcmp(n->rss_data.key, vnet_mig->rss_key_early,
+               VIRTIO_NET_RSS_MAX_KEY_SIZE) != 0) {
+        return true;
+    }
+    if (n->rss_data.indirections_len) {
+        size_t bytes = (size_t)n->rss_data.indirections_len * sizeof(uint16_t);
+
+        /* If either side lacks a buffer when len > 0, treat as changed */
+        if (!n->rss_data.indirections_table ||
+            !vnet_mig->rss_indirections_table_early) {
+            return true;
+        }
+        if (memcmp(n->rss_data.indirections_table,
+                   vnet_mig->rss_indirections_table_early, bytes) != 0) {
+            return true;
+        }
+    }
+
     /*
      * Always return true for now until we're able to detect all possible
      * changes to a VirtIONet device.
diff --git a/include/hw/virtio/virtio-net.h b/include/hw/virtio/virtio-net.h
index 5d6179fa19..88074a0976 100644
--- a/include/hw/virtio/virtio-net.h
+++ b/include/hw/virtio/virtio-net.h
@@ -180,6 +180,14 @@ typedef struct VirtIONetQueue {
  * @guest_offloads_early: Guest offloads snapshot.
  * @mq_early: Multiqueue state snapshot.
  * @queue_pairs_early: Queue pairs snapshot.
+ * @rss_enabled_early: RSS enabled flag.
+ * @rss_redirect_early: RSS redirect flag.
+ * @rss_populate_hash_early: RSS populate hash flag.
+ * @rss_runtime_hash_types_early: RSS runtime hash types.
+ * @rss_indirections_len_early: RSS indirections length.
+ * @rss_default_queue_early: RSS default queue.
+ * @rss_key_early: RSS key.
+ * @rss_indirections_table_early: RSS indirections table.
  */
 typedef struct VirtIONetMigration {
     uint16_t status_early;
@@ -193,6 +201,14 @@ typedef struct VirtIONetMigration {
     uint64_t guest_offloads_early;
     int mq_early;
     uint16_t queue_pairs_early;
+    bool rss_enabled_early;
+    bool rss_redirect_early;
+    bool rss_populate_hash_early;
+    uint32_t rss_runtime_hash_types_early;
+    uint16_t rss_indirections_len_early;
+    uint16_t rss_default_queue_early;
+    uint8_t rss_key_early[VIRTIO_NET_RSS_MAX_KEY_SIZE];
+    uint16_t *rss_indirections_table_early;
 } VirtIONetMigration;
 
 struct VirtIONet {
-- 
2.51.0