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migration: preserve suspended for snapshot

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Restoring a snapshot can break a suspended guest.  Snapshots suffer from
the same suspended-state issues that affect live migration, plus they must
handle an additional problematic scenario, which is that a running vm must
remain running if it loads a suspended snapshot.

To save, the existing vm_stop call now completely stops the suspended
state.  Finish with vm_resume to leave the vm in the state it had prior
to the save, correctly restoring the suspended state.

To load, if the snapshot is not suspended, then vm_stop + vm_resume
correctly handles all states, and leaves the vm in the state it had prior
to the load.  However, if the snapshot is suspended, restoration is
trickier.  First, call vm_resume to restore the state to suspended so the
current state matches the saved state.  Then, if the pre-load state is
running, call wakeup to resume running.

Prior to these changes, the vm_stop to RUN_STATE_SAVE_VM and
RUN_STATE_RESTORE_VM did not change runstate if the current state was
suspended, but now it does, so allow these transitions.

Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Link: https://lore.kernel.org/r/1704312341-66640-8-git-send-email-steven.sistare@oracle.com
Signed-off-by: Peter Xu <peterx@redhat.com>
This commit is contained in:
Steve Sistare 2024-01-03 12:05:36 -08:00 • committed by Peter Xu
parent b4e9ddccd1
commit 58b105703e
5 changed files with 32 additions and 13 deletions
Download patch file Download diff file Expand all files Collapse all files

23
migration/savevm.c
View file

@ -3046,7 +3046,7 @@ bool save_snapshot(const char *name, bool overwrite, const char *vmstate,
QEMUSnapshotInfo sn1, *sn = &sn1;
int ret = -1, ret2;
QEMUFile *f;
int saved_vm_running;
RunState saved_state = runstate_get();
uint64_t vm_state_size;
g_autoptr(GDateTime) now = g_date_time_new_now_local();
@ -3092,8 +3092,6 @@ bool save_snapshot(const char *name, bool overwrite, const char *vmstate,
return false;
}
saved_vm_running = runstate_is_running();
global_state_store();
vm_stop(RUN_STATE_SAVE_VM);
@ -3147,9 +3145,7 @@ bool save_snapshot(const char *name, bool overwrite, const char *vmstate,
the_end:
bdrv_drain_all_end();
if (saved_vm_running) {
vm_start();
}
vm_resume(saved_state);
return ret == 0;
}
@ -3317,6 +3313,14 @@ err_drain:
return false;
}
void load_snapshot_resume(RunState state)
{
vm_resume(state);
if (state == RUN_STATE_RUNNING && runstate_get() == RUN_STATE_SUSPENDED) {
qemu_system_wakeup_request(QEMU_WAKEUP_REASON_OTHER, &error_abort);
}
}
bool delete_snapshot(const char *name, bool has_devices,
strList *devices, Error **errp)
{
@ -3381,16 +3385,15 @@ static void snapshot_load_job_bh(void *opaque)
{
Job *job = opaque;
SnapshotJob *s = container_of(job, SnapshotJob, common);
int orig_vm_running;
RunState orig_state = runstate_get();
job_progress_set_remaining(&s->common, 1);
orig_vm_running = runstate_is_running();
vm_stop(RUN_STATE_RESTORE_VM);
s->ret = load_snapshot(s->tag, s->vmstate, true, s->devices, s->errp);
if (s->ret && orig_vm_running) {
vm_start();
if (s->ret) {
load_snapshot_resume(orig_state);
}
job_progress_update(&s->common, 1);