vhost-user: Add 'VHOST_USER_POSTCOPY_ADVISE' message

Wire up a notifier to send a VHOST_USER_POSTCOPY_ADVISE
message on an incoming advise.

Later patches will fill in the behaviour/contents of the
message.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

contrib/libvhost-user/libvhost-user.c

@@ -86,6 +86,7 @@ vu_request_to_string(unsigned int req)
         REQ(VHOST_USER_SET_VRING_ENDIAN),
         REQ(VHOST_USER_GET_CONFIG),
         REQ(VHOST_USER_SET_CONFIG),
+        REQ(VHOST_USER_POSTCOPY_ADVISE),
         REQ(VHOST_USER_MAX),
     };
 #undef REQ
@@ -856,6 +857,14 @@ vu_set_config(VuDev *dev, VhostUserMsg *vmsg)
     return false;
 }
 
+static bool
+vu_set_postcopy_advise(VuDev *dev, VhostUserMsg *vmsg)
+{
+    /* TODO: Open ufd, pass it back in the request */
+    vmsg->size = 0;
+    return true; /* = send a reply */
+}
+
 static bool
 vu_process_message(VuDev *dev, VhostUserMsg *vmsg)
 {
@@ -927,6 +936,8 @@ vu_process_message(VuDev *dev, VhostUserMsg *vmsg)
         return vu_set_config(dev, vmsg);
     case VHOST_USER_NONE:
         break;
+    case VHOST_USER_POSTCOPY_ADVISE:
+        return vu_set_postcopy_advise(dev, vmsg);
     default:
         vmsg_close_fds(vmsg);
         vu_panic(dev, "Unhandled request: %d", vmsg->request);

contrib/libvhost-user/libvhost-user.h

@@ -83,6 +83,9 @@ typedef enum VhostUserRequest {
     VHOST_USER_SET_VRING_ENDIAN = 23,
     VHOST_USER_GET_CONFIG = 24,
     VHOST_USER_SET_CONFIG = 25,
+    VHOST_USER_CREATE_CRYPTO_SESSION = 26,
+    VHOST_USER_CLOSE_CRYPTO_SESSION = 27,
+    VHOST_USER_POSTCOPY_ADVISE  = 28,
     VHOST_USER_MAX
 } VhostUserRequest;
 

docs/interop/vhost-user.txt

@@ -699,6 +699,16 @@ Master message types
      feature has been successfully negotiated.
      It's a required feature for crypto devices.
 
+ * VHOST_USER_POSTCOPY_ADVISE
+      Id: 28
+      Master payload: N/A
+      Slave payload: userfault fd
+
+      When VHOST_USER_PROTOCOL_F_PAGEFAULT is supported, the
+      master advises slave that a migration with postcopy enabled is underway,
+      the slave must open a userfaultfd for later use.
+      Note that at this stage the migration is still in precopy mode.
+
 Slave message types
 -------------------
 

hw/virtio/vhost-user.c

@@ -78,6 +78,7 @@ typedef enum VhostUserRequest {
     VHOST_USER_SET_CONFIG = 25,
     VHOST_USER_CREATE_CRYPTO_SESSION = 26,
     VHOST_USER_CLOSE_CRYPTO_SESSION = 27,
+    VHOST_USER_POSTCOPY_ADVISE  = 28,
     VHOST_USER_MAX
 } VhostUserRequest;
 
@@ -795,6 +796,50 @@ out:
     return ret;
 }
 
+/*
+ * Called at the start of an inbound postcopy on reception of the
+ * 'advise' command.
+ */
+static int vhost_user_postcopy_advise(struct vhost_dev *dev, Error **errp)
+{
+    struct vhost_user *u = dev->opaque;
+    CharBackend *chr = u->chr;
+    int ufd;
+    VhostUserMsg msg = {
+        .hdr.request = VHOST_USER_POSTCOPY_ADVISE,
+        .hdr.flags = VHOST_USER_VERSION,
+    };
+
+    if (vhost_user_write(dev, &msg, NULL, 0) < 0) {
+        error_setg(errp, "Failed to send postcopy_advise to vhost");
+        return -1;
+    }
+
+    if (vhost_user_read(dev, &msg) < 0) {
+        error_setg(errp, "Failed to get postcopy_advise reply from vhost");
+        return -1;
+    }
+
+    if (msg.hdr.request != VHOST_USER_POSTCOPY_ADVISE) {
+        error_setg(errp, "Unexpected msg type. Expected %d received %d",
+                     VHOST_USER_POSTCOPY_ADVISE, msg.hdr.request);
+        return -1;
+    }
+
+    if (msg.hdr.size) {
+        error_setg(errp, "Received bad msg size.");
+        return -1;
+    }
+    ufd = qemu_chr_fe_get_msgfd(chr);
+    if (ufd < 0) {
+        error_setg(errp, "%s: Failed to get ufd", __func__);
+        return -1;
+    }
+
+    /* TODO: register ufd with userfault thread */
+    return 0;
+}
+
 static int vhost_user_postcopy_notifier(NotifierWithReturn *notifier,
                                         void *opaque)
 {
@@ -814,6 +859,9 @@ static int vhost_user_postcopy_notifier(NotifierWithReturn *notifier,
         }
         break;
 
+    case POSTCOPY_NOTIFY_INBOUND_ADVISE:
+        return vhost_user_postcopy_advise(dev, pnd->errp);
+
     default:
         /* We ignore notifications we don't know */
         break;

migration/postcopy-ram.h

@@ -130,6 +130,7 @@ void postcopy_infrastructure_init(void);
  */
 enum PostcopyNotifyReason {
     POSTCOPY_NOTIFY_PROBE = 0,
+    POSTCOPY_NOTIFY_INBOUND_ADVISE,
 };
 
 struct PostcopyNotifyData {

migration/savevm.c

@@ -1386,6 +1386,7 @@ static int loadvm_postcopy_handle_advise(MigrationIncomingState *mis,
 {
     PostcopyState ps = postcopy_state_set(POSTCOPY_INCOMING_ADVISE);
     uint64_t remote_pagesize_summary, local_pagesize_summary, remote_tps;
+    Error *local_err = NULL;
 
     trace_loadvm_postcopy_handle_advise();
     if (ps != POSTCOPY_INCOMING_NONE) {
@@ -1451,6 +1452,11 @@ static int loadvm_postcopy_handle_advise(MigrationIncomingState *mis,
         return -1;
     }
 
+    if (postcopy_notify(POSTCOPY_NOTIFY_INBOUND_ADVISE, &local_err)) {
+        error_report_err(local_err);
+        return -1;
+    }
+
     if (ram_postcopy_incoming_init(mis)) {
         return -1;
     }