vhost+postcopy: Transmit 'listen' to slave

Notify the vhost-user slave on reception of the 'postcopy-listen'
event from the source.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Peter Xu <peterx@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

@@ -98,6 +98,7 @@ vu_request_to_string(unsigned int req)
         REQ(VHOST_USER_GET_CONFIG),
         REQ(VHOST_USER_SET_CONFIG),
         REQ(VHOST_USER_POSTCOPY_ADVISE),
+        REQ(VHOST_USER_POSTCOPY_LISTEN),
         REQ(VHOST_USER_MAX),
     };
 #undef REQ
@@ -931,6 +932,22 @@ out:
     return true; /* = send a reply */
 }
 
+static bool
+vu_set_postcopy_listen(VuDev *dev, VhostUserMsg *vmsg)
+{
+    vmsg->payload.u64 = -1;
+    vmsg->size = sizeof(vmsg->payload.u64);
+
+    if (dev->nregions) {
+        vu_panic(dev, "Regions already registered at postcopy-listen");
+        return true;
+    }
+    dev->postcopy_listening = true;
+
+    vmsg->flags = VHOST_USER_VERSION |  VHOST_USER_REPLY_MASK;
+    vmsg->payload.u64 = 0; /* Success */
+    return true;
+}
 static bool
 vu_process_message(VuDev *dev, VhostUserMsg *vmsg)
 {
@@ -1004,6 +1021,8 @@ vu_process_message(VuDev *dev, VhostUserMsg *vmsg)
         break;
     case VHOST_USER_POSTCOPY_ADVISE:
         return vu_set_postcopy_advise(dev, vmsg);
+    case VHOST_USER_POSTCOPY_LISTEN:
+        return vu_set_postcopy_listen(dev, vmsg);
     default:
         vmsg_close_fds(vmsg);
         vu_panic(dev, "Unhandled request: %d", vmsg->request);

contrib/libvhost-user/libvhost-user.h

@@ -86,6 +86,7 @@ typedef enum VhostUserRequest {
     VHOST_USER_CREATE_CRYPTO_SESSION = 26,
     VHOST_USER_CLOSE_CRYPTO_SESSION = 27,
     VHOST_USER_POSTCOPY_ADVISE  = 28,
+    VHOST_USER_POSTCOPY_LISTEN  = 29,
     VHOST_USER_MAX
 } VhostUserRequest;
 
@@ -285,6 +286,7 @@ struct VuDev {
 
     /* Postcopy data */
     int postcopy_ufd;
+    bool postcopy_listening;
 };
 
 typedef struct VuVirtqElement {

docs/interop/vhost-user.txt

@@ -709,6 +709,17 @@ Master message types
       the slave must open a userfaultfd for later use.
       Note that at this stage the migration is still in precopy mode.
 
+ * VHOST_USER_POSTCOPY_LISTEN
+      Id: 29
+      Master payload: N/A
+
+      Master advises slave that a transition to postcopy mode has happened.
+      The slave must ensure that shared memory is registered with userfaultfd
+      to cause faulting of non-present pages.
+
+      This is always sent sometime after a VHOST_USER_POSTCOPY_ADVISE, and
+      thus only when VHOST_USER_PROTOCOL_F_PAGEFAULT is supported.
+
 Slave message types
 -------------------
 

hw/virtio/trace-events

@@ -6,6 +6,9 @@ vhost_region_add_section(const char *name, uint64_t gpa, uint64_t size, uint64_t
 vhost_region_add_section_abut(const char *name, uint64_t new_size) "%s: 0x%"PRIx64
 vhost_section(const char *name, int r) "%s:%d"
 
+# hw/virtio/vhost-user.c
+vhost_user_postcopy_listen(void) ""
+
 # hw/virtio/virtio.c
 virtqueue_alloc_element(void *elem, size_t sz, unsigned in_num, unsigned out_num) "elem %p size %zd in_num %u out_num %u"
 virtqueue_fill(void *vq, const void *elem, unsigned int len, unsigned int idx) "vq %p elem %p len %u idx %u"

hw/virtio/vhost-user.c

@@ -20,6 +20,7 @@
 #include "sysemu/cryptodev.h"
 #include "migration/migration.h"
 #include "migration/postcopy-ram.h"
+#include "trace.h"
 
 #include <sys/ioctl.h>
 #include <sys/socket.h>
@@ -79,6 +80,7 @@ typedef enum VhostUserRequest {
     VHOST_USER_CREATE_CRYPTO_SESSION = 26,
     VHOST_USER_CLOSE_CRYPTO_SESSION = 27,
     VHOST_USER_POSTCOPY_ADVISE  = 28,
+    VHOST_USER_POSTCOPY_LISTEN  = 29,
     VHOST_USER_MAX
 } VhostUserRequest;
 
@@ -172,6 +174,8 @@ struct vhost_user {
     int slave_fd;
     NotifierWithReturn postcopy_notifier;
     struct PostCopyFD  postcopy_fd;
+    /* True once we've entered postcopy_listen */
+    bool               postcopy_listen;
 };
 
 static bool ioeventfd_enabled(void)
@@ -858,6 +862,33 @@ static int vhost_user_postcopy_advise(struct vhost_dev *dev, Error **errp)
     return 0;
 }
 
+/*
+ * Called at the switch to postcopy on reception of the 'listen' command.
+ */
+static int vhost_user_postcopy_listen(struct vhost_dev *dev, Error **errp)
+{
+    struct vhost_user *u = dev->opaque;
+    int ret;
+    VhostUserMsg msg = {
+        .hdr.request = VHOST_USER_POSTCOPY_LISTEN,
+        .hdr.flags = VHOST_USER_VERSION | VHOST_USER_NEED_REPLY_MASK,
+    };
+    u->postcopy_listen = true;
+    trace_vhost_user_postcopy_listen();
+    if (vhost_user_write(dev, &msg, NULL, 0) < 0) {
+        error_setg(errp, "Failed to send postcopy_listen to vhost");
+        return -1;
+    }
+
+    ret = process_message_reply(dev, &msg);
+    if (ret) {
+        error_setg(errp, "Failed to receive reply to postcopy_listen");
+        return ret;
+    }
+
+    return 0;
+}
+
 static int vhost_user_postcopy_notifier(NotifierWithReturn *notifier,
                                         void *opaque)
 {
@@ -880,6 +911,9 @@ static int vhost_user_postcopy_notifier(NotifierWithReturn *notifier,
     case POSTCOPY_NOTIFY_INBOUND_ADVISE:
         return vhost_user_postcopy_advise(dev, pnd->errp);
 
+    case POSTCOPY_NOTIFY_INBOUND_LISTEN:
+        return vhost_user_postcopy_listen(dev, pnd->errp);
+
     default:
         /* We ignore notifications we don't know */
         break;

migration/postcopy-ram.h

@@ -131,6 +131,7 @@ void postcopy_infrastructure_init(void);
 enum PostcopyNotifyReason {
     POSTCOPY_NOTIFY_PROBE = 0,
     POSTCOPY_NOTIFY_INBOUND_ADVISE,
+    POSTCOPY_NOTIFY_INBOUND_LISTEN,
 };
 
 struct PostcopyNotifyData {

migration/savevm.c

@@ -1618,6 +1618,8 @@ static int loadvm_postcopy_handle_listen(MigrationIncomingState *mis)
 {
     PostcopyState ps = postcopy_state_set(POSTCOPY_INCOMING_LISTENING);
     trace_loadvm_postcopy_handle_listen();
+    Error *local_err = NULL;
+
     if (ps != POSTCOPY_INCOMING_ADVISE && ps != POSTCOPY_INCOMING_DISCARD) {
         error_report("CMD_POSTCOPY_LISTEN in wrong postcopy state (%d)", ps);
         return -1;
@@ -1643,6 +1645,11 @@ static int loadvm_postcopy_handle_listen(MigrationIncomingState *mis)
         }
     }
 
+    if (postcopy_notify(POSTCOPY_NOTIFY_INBOUND_LISTEN, &local_err)) {
+        error_report_err(local_err);
+        return -1;
+    }
+
     if (mis->have_listen_thread) {
         error_report("CMD_POSTCOPY_RAM_LISTEN already has a listen thread");
         return -1;