Merge tag 'migration-20240407-pull-request' of https://gitlab.com/peterx/qemu into staging

Migration pull for 9.0-rc3

- Wei/Lei's fix on a rare postcopy race that can hang the channel (since 8.0)
- Avihai's fix on maintainers file, points to the right doc links

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* tag 'migration-20240407-pull-request' of https://gitlab.com/peterx/qemu:
  MAINTAINERS: Adjust migration documentation files
  migration/postcopy: ensure preempt channel is ready before loading states

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

2 files changed, 25 insertions, 2 deletions

diff --git a/MAINTAINERS b/MAINTAINERS
index e71183eef9..d3fc2a06e3 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -2170,7 +2170,7 @@ S: Supported
 F: hw/vfio/*
 F: include/hw/vfio/
 F: docs/igd-assign.txt
-F: docs/devel/vfio-migration.rst
+F: docs/devel/migration/vfio.rst
 
 vfio-ccw
 M: Eric Farman <farman@linux.ibm.com>
@@ -2231,6 +2231,7 @@ F: qapi/virtio.json
 F: net/vhost-user.c
 F: include/hw/virtio/
 F: docs/devel/virtio*
+F: docs/devel/migration/virtio.rst
 
 virtio-balloon
 M: Michael S. Tsirkin <mst@redhat.com>
@@ -3422,7 +3423,7 @@ F: migration/
 F: scripts/vmstate-static-checker.py
 F: tests/vmstate-static-checker-data/
 F: tests/qtest/migration-test.c
-F: docs/devel/migration.rst
+F: docs/devel/migration/
 F: qapi/migration.json
 F: tests/migration/
 F: util/userfaultfd.c
@@ -3442,6 +3443,7 @@ F: include/sysemu/dirtylimit.h
 F: migration/dirtyrate.c
 F: migration/dirtyrate.h
 F: include/sysemu/dirtyrate.h
+F: docs/devel/migration/dirty-limit.rst
 
 Detached LUKS header
 M: Hyman Huang <yong.huang@smartx.com>
diff --git a/migration/savevm.c b/migration/savevm.c
index 388d7af7cd..e7c1215671 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -2342,6 +2342,27 @@ static int loadvm_handle_cmd_packaged(MigrationIncomingState *mis)
 
     QEMUFile *packf = qemu_file_new_input(QIO_CHANNEL(bioc));
 
+    /*
+     * Before loading the guest states, ensure that the preempt channel has
+     * been ready to use, as some of the states (e.g. via virtio_load) might
+     * trigger page faults that will be handled through the preempt channel.
+     * So yield to the main thread in the case that the channel create event
+     * hasn't been dispatched.
+     *
+     * TODO: if we can move migration loadvm out of main thread, then we
+     * won't block main thread from polling the accept() fds.  We can drop
+     * this as a whole when that is done.
+     */
+    do {
+        if (!migrate_postcopy_preempt() || !qemu_in_coroutine() ||
+            mis->postcopy_qemufile_dst) {
+            break;
+        }
+
+        aio_co_schedule(qemu_get_current_aio_context(), qemu_coroutine_self());
+        qemu_coroutine_yield();
+    } while (1);
+
     ret = qemu_loadvm_state_main(packf, mis);
     trace_loadvm_handle_cmd_packaged_main(ret);
     qemu_fclose(packf);