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authorWei Wang <wei.w.wang@intel.com>2024-04-05 11:40:56 +0800
committerPeter Xu <peterx@redhat.com>2024-04-07 14:40:25 -0400
commit7afbdada7effbc2b97281bfbce0c6df351a3cf88 (patch)
tree692fddbda9eb3bd79448fde2b5e233624416b085
parentce64e6224affb8b4e4b019f76d2950270b391af5 (diff)
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migration/postcopy: ensure preempt channel is ready before loading states
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>
-rw-r--r--migration/savevm.c21
1 files changed, 21 insertions, 0 deletions
diff --git a/migration/savevm.c b/migration/savevm.c
index 388d7af..e7c1215 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);