[PATCH v3 1/2] vdpa: Restore hash calculation state

[Hawkins Jiawei <yin31149@gmail.com>]

This patch introduces vhost_vdpa_net_load_rss() to restore
the hash calculation state at device's startup.

Signed-off-by: Hawkins Jiawei <yin31149@gmail.com>
---
v3:
  - remove the `do_rss` argument in vhost_vdpa_net_load_rss()
  - zero reserved fields in "cfg" manually instead of using memset()
to prevent compiler "array-bounds" warning

v2: https://lore.kernel.org/all/f5ffad10699001107022851e0560cb394039d6b0.1693297766.git.yin31149@gmail.com/
  - resolve conflict with updated patch
"vdpa: Send all CVQ state load commands in parallel"
  - move the `table` declaration at the beginning of the
vhost_vdpa_net_load_rss()

RFC: https://lore.kernel.org/all/a54ca70b12ebe2f3c391864e41241697ab1aba30.1691762906.git.yin31149@gmail.com/

 net/vhost-vdpa.c | 89 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 89 insertions(+)

diff --git a/net/vhost-vdpa.c b/net/vhost-vdpa.c
index 4b7c3b81b8..2e4bad65b4 100644
--- a/net/vhost-vdpa.c
+++ b/net/vhost-vdpa.c
@@ -817,6 +817,86 @@ static int vhost_vdpa_net_load_mac(VhostVDPAState *s, const VirtIONet *n,
     return 0;
 }
 
+static int vhost_vdpa_net_load_rss(VhostVDPAState *s, const VirtIONet *n,
+                                   struct iovec *out_cursor,
+                                   struct iovec *in_cursor)
+{
+    struct virtio_net_rss_config cfg;
+    ssize_t r;
+    g_autofree uint16_t *table = NULL;
+
+    /*
+     * According to VirtIO standard, "Initially the device has all hash
+     * types disabled and reports only VIRTIO_NET_HASH_REPORT_NONE.".
+     *
+     * Therefore, there is no need to send this CVQ command if the
+     * driver disable the all hash types, which aligns with
+     * the device's defaults.
+     *
+     * Note that the device's defaults can mismatch the driver's
+     * configuration only at live migration.
+     */
+    if (!n->rss_data.enabled ||
+        n->rss_data.hash_types == VIRTIO_NET_HASH_REPORT_NONE) {
+        return 0;
+    }
+
+    table = g_malloc_n(n->rss_data.indirections_len,
+                       sizeof(n->rss_data.indirections_table[0]));
+    cfg.hash_types = cpu_to_le32(n->rss_data.hash_types);
+
+    /*
+     * According to VirtIO standard, "Field reserved MUST contain zeroes.
+     * It is defined to make the structure to match the layout of
+     * virtio_net_rss_config structure, defined in 5.1.6.5.7.".
+     *
+     * Therefore, we need to zero the fields in struct virtio_net_rss_config,
+     * which corresponds the `reserved` field in
+     * struct virtio_net_hash_config.
+     */
+    cfg.indirection_table_mask = 0;
+    cfg.unclassified_queue = 0;
+    table[0] = 0; /* the actual indirection table for cfg */
+    cfg.max_tx_vq = 0;
+
+    /*
+     * Consider that virtio_net_handle_rss() currently does not restore the
+     * hash key length parsed from the CVQ command sent from the guest into
+     * n->rss_data and uses the maximum key length in other code, so we also
+     * employthe the maxium key length here.
+     */
+    cfg.hash_key_length = sizeof(n->rss_data.key);
+
+    const struct iovec data[] = {
+        {
+            .iov_base = &cfg,
+            .iov_len = offsetof(struct virtio_net_rss_config,
+                                indirection_table),
+        }, {
+            .iov_base = table,
+            .iov_len = n->rss_data.indirections_len *
+                       sizeof(n->rss_data.indirections_table[0]),
+        }, {
+            .iov_base = &cfg.max_tx_vq,
+            .iov_len = offsetof(struct virtio_net_rss_config, hash_key_data) -
+                       offsetof(struct virtio_net_rss_config, max_tx_vq),
+        }, {
+            .iov_base = (void *)n->rss_data.key,
+            .iov_len = sizeof(n->rss_data.key),
+        }
+    };
+
+    r = vhost_vdpa_net_load_cmd(s, out_cursor, in_cursor,
+                                VIRTIO_NET_CTRL_MQ,
+                                VIRTIO_NET_CTRL_MQ_HASH_CONFIG,
+                                data, ARRAY_SIZE(data));
+    if (unlikely(r < 0)) {
+        return r;
+    }
+
+    return 0;
+}
+
 static int vhost_vdpa_net_load_mq(VhostVDPAState *s,
                                   const VirtIONet *n,
                                   struct iovec *out_cursor,
@@ -842,6 +922,15 @@ static int vhost_vdpa_net_load_mq(VhostVDPAState *s,
         return r;
     }
 
+    if (!virtio_vdev_has_feature(&n->parent_obj, VIRTIO_NET_F_HASH_REPORT)) {
+        return 0;
+    }
+
+    r = vhost_vdpa_net_load_rss(s, n, out_cursor, in_cursor);
+    if (unlikely(r < 0)) {
+        return r;
+    }
+
     return 0;
 }
 
-- 
2.25.1