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migration/postcopy: ensure preempt channel is ready before loading states

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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>
This commit is contained in:
Wei Wang 2024-04-05 11:40:56 +08:00 committed by Peter Xu
parent ce64e6224a
commit 7afbdada7e
1 changed files with 21 additions and 0 deletions
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21
migration/savevm.c
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@ -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);