From: "Dr. David Alan Gilbert" <dgilb...@redhat.com>
The loading of a device state (during postcopy) may access guest
memory that's still on the source machine and thus might need
a page fill; split off a separate thread that handles the incoming
page data so that the original incoming migration code can finish
off the device data.
Signed-off-by: Dr. David Alan Gilbert <dgilb...@redhat.com>
---
include/migration/migration.h | 4 +++
migration/migration.c | 6 ++++
migration/savevm.c | 79 ++++++++++++++++++++++++++++++++++++++++++-
trace-events | 2 ++
4 files changed, 90 insertions(+), 1 deletion(-)
diff --git a/include/migration/migration.h b/include/migration/migration.h
index 4f954ca..da6529d 100644
--- a/include/migration/migration.h
+++ b/include/migration/migration.h
@@ -75,6 +75,10 @@ struct MigrationIncomingState {
QemuThread fault_thread;
QemuSemaphore fault_thread_sem;
+ bool have_listen_thread;
+ QemuThread listen_thread;
+ QemuSemaphore listen_thread_sem;
+
/* For the kernel to send us notifications */
int userfault_fd;
/* To tell the fault_thread to quit */
diff --git a/migration/migration.c b/migration/migration.c
index 7fa982e..e908b50 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -1222,6 +1222,12 @@ static int postcopy_start(MigrationState *ms, bool
*old_vm_running)
goto fail;
}
+ /*
+ * Make sure the receiver can get incoming pages before we send the rest
+ * of the state
+ */
+ qemu_savevm_send_postcopy_listen(fb);
+
qemu_savevm_state_complete_precopy(fb);
qemu_savevm_send_ping(fb, 3);
diff --git a/migration/savevm.c b/migration/savevm.c
index b87238a..258c551 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -1314,6 +1314,65 @@ static int
loadvm_postcopy_ram_handle_discard(MigrationIncomingState *mis,
return 0;
}
+/*
+ * Triggered by a postcopy_listen command; this thread takes over reading
+ * the input stream, leaving the main thread free to carry on loading the rest
+ * of the device state (from RAM).
+ * (TODO:This could do with being in a postcopy file - but there again it's
+ * just another input loop, not that postcopy specific)
+ */
+static void *postcopy_ram_listen_thread(void *opaque)
+{
+ QEMUFile *f = opaque;
+ MigrationIncomingState *mis = migration_incoming_get_current();
+ int load_res;
+
+ qemu_sem_post(&mis->listen_thread_sem);
+ trace_postcopy_ram_listen_thread_start();
+
+ /*
+ * Because we're a thread and not a coroutine we can't yield
+ * in qemu_file, and thus we must be blocking now.
+ */
+ qemu_file_change_blocking(f, true);
+ load_res = qemu_loadvm_state_main(f, mis);
+ /* And non-blocking again so we don't block in any cleanup */
+ qemu_file_change_blocking(f, false);
+
+ trace_postcopy_ram_listen_thread_exit();
+ if (load_res < 0) {
+ error_report("%s: loadvm failed: %d", __func__, load_res);
+ qemu_file_set_error(f, load_res);
+ } else {
+ /*
+ * This looks good, but it's possible that the device loading in the
+ * main thread hasn't finished yet, and so we might not be in 'RUN'
+ * state yet; wait for the end of the main thread.
+ */
+ qemu_event_wait(&mis->main_thread_load_event);
+ }
+ postcopy_ram_incoming_cleanup(mis);
+ /*
+ * If everything has worked fine, then the main thread has waited
+ * for us to start, and we're the last use of the mis.
+ * (If something broke then qemu will have to exit anyway since it's
+ * got a bad migration state).
+ */
+ migration_incoming_state_destroy();
+
+ if (load_res < 0) {
+ /*
+ * If something went wrong then we have a bad state so exit;
+ * depending how far we got it might be possible at this point
+ * to leave the guest running and fire MCEs for pages that never
+ * arrived as a desperate recovery step.
+ */
+ exit(EXIT_FAILURE);
+ }
+
+ return NULL;
+}
+
/* After this message we must be able to immediately receive postcopy data */
static int loadvm_postcopy_handle_listen(MigrationIncomingState *mis)
{
@@ -1333,7 +1392,20 @@ static int
loadvm_postcopy_handle_listen(MigrationIncomingState *mis)
return -1;
}
- /* TODO start up the postcopy listening thread */
+ if (mis->have_listen_thread) {
+ error_report("CMD_POSTCOPY_RAM_LISTEN already has a listen thread");
+ return -1;
+ }
+
+ mis->have_listen_thread = true;
+ /* Start up the listening thread and wait for it to signal ready */
+ qemu_sem_init(&mis->listen_thread_sem, 0);
+ qemu_thread_create(&mis->listen_thread, "postcopy/listen",
+ postcopy_ram_listen_thread, mis->file,
+ QEMU_THREAD_JOINABLE);
+ qemu_sem_wait(&mis->listen_thread_sem);
+ qemu_sem_destroy(&mis->listen_thread_sem);
+
return 0;
}
@@ -1657,6 +1729,11 @@ int qemu_loadvm_state(QEMUFile *f)
qemu_event_set(&mis->main_thread_load_event);
trace_qemu_loadvm_state_post_main(ret);
+ if (mis->have_listen_thread) {
+ /* Listen thread still going, can't clean up yet */
+ return ret;
+ }
+
if (ret == 0) {
int file_error_after_eof = qemu_file_get_error(f);
diff --git a/trace-events b/trace-events
index ab201f9..a6c7839 100644
--- a/trace-events
+++ b/trace-events
@@ -1199,6 +1199,8 @@ loadvm_postcopy_ram_handle_discard_end(void) ""
loadvm_postcopy_ram_handle_discard_header(const char *ramid, uint16_t len)
"%s: %ud"
loadvm_process_command(uint16_t com, uint16_t len) "com=0x%x len=%d"
loadvm_process_command_ping(uint32_t val) "%x"
+postcopy_ram_listen_thread_exit(void) ""
+postcopy_ram_listen_thread_start(void) ""
qemu_savevm_send_postcopy_advise(void) ""
qemu_savevm_send_postcopy_ram_discard(const char *id, uint16_t len) "%s: %ud"
savevm_section_start(const char *id, unsigned int section_id) "%s, section_id
%u"
--
2.4.3
