diff mbox series

[Stable-8.2.3,82/87] migration/postcopy: ensure preempt channel is ready before loading states

Message ID 20240410072303.4191455-82-mjt@tls.msk.ru
State New
Headers show
Series Patch Round-up for stable 8.2.3, freeze on 2024-04-20 | expand

Commit Message

Michael Tokarev April 10, 2024, 7:22 a.m. UTC 
From: Wei Wang <wei.w.wang@intel.com>

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.

Cc: qemu-stable <qemu-stable@nongnu.org>
Fixes: 9358982744 ("migration: Send requested page directly in rp-return thread")
Originally-by: Lei Wang <lei4.wang@intel.com>
Link: https://lore.kernel.org/all/9aa5d1be-7801-40dd-83fd-f7e041ced249@intel.com/T/
Signed-off-by: Lei Wang <lei4.wang@intel.com>
Signed-off-by: Wei Wang <wei.w.wang@intel.com>
Link: https://lore.kernel.org/r/20240405034056.23933-1-wei.w.wang@intel.com
[peterx: add a todo section, add Fixes and copy stable for 8.0+]
Signed-off-by: Peter Xu <peterx@redhat.com>
(cherry picked from commit 7afbdada7effbc2b97281bfbce0c6df351a3cf88)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
diff mbox series

Patch

diff --git a/migration/savevm.c b/migration/savevm.c
index eec5503a42..f374da85b9 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -2343,6 +2343,27 @@  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);