[RFC PATCH 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.

Note that vhost_vdpa_net_load_rss() has `do_rss` argument,
which allows future code to reuse this function to restore
the receive-side scaling state when the VIRTIO_NET_F_RSS
feature is enabled in SVQ. Currently, vhost_vdpa_net_load_rss()
could only be invoked when `do_rss` is set to false.

Signed-off-by: Hawkins Jiawei <yin31149@gmail.com>
---
Question:

It seems 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 for `hash_key_length` field in VIRTIO_NET_CTRL_MQ_HASH_CONFIG command
sent to device, is it okay to also use the maximum key length as its value?
Or should we introduce the `hash_key_length` field in n->rss_data
structure to record the key length from guest and use this value?

 net/vhost-vdpa.c | 88 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 88 insertions(+)

diff --git a/net/vhost-vdpa.c b/net/vhost-vdpa.c
index 7bb29f6009..bd51020771 100644
--- a/net/vhost-vdpa.c
+++ b/net/vhost-vdpa.c
@@ -788,6 +788,85 @@ 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,
+                                   void **out_cursor, void **in_cursor,
+                                   bool do_rss)
+{
+    struct virtio_net_rss_config cfg;
+    ssize_t r;
+
+    /*
+     * 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;
+    }
+
+    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.
+     */
+    memset(&cfg.indirection_table_mask, 0,
+           sizeof_field(struct virtio_net_hash_config, reserved));
+    /*
+     * 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);
+
+    g_autofree uint16_t *table = g_malloc_n(n->rss_data.indirections_len,
+                                    sizeof(n->rss_data.indirections_table[0]));
+    for (int i = 0; i < n->rss_data.indirections_len; ++i) {
+        table[i] = cpu_to_le16(n->rss_data.indirections_table[i]);
+    }
+
+    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,
                                   void **out_cursor, void **in_cursor)
@@ -812,6 +891,15 @@ 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, false);
+    if (unlikely(r < 0)) {
+        return r;
+    }
+
     return 0;
 }
 
-- 
2.25.1