xenbus: Use .freeze/.thaw to handle xenbus devices

[ Upstream commit e08dd1e ]

The goal is to fix s2idle and S3 for Xen PV devices.  A domain resuming
from s3 or s2idle disconnects its PV devices during resume.  The
backends are not expecting this and do not reconnect.

b3e96c0 ("xen: use freeze/restore/thaw PM events for suspend/
resume/chkpt") changed xen_suspend()/do_suspend() from
PMSG_SUSPEND/PMSG_RESUME to PMSG_FREEZE/PMSG_THAW/PMSG_RESTORE, but the
suspend/resume callbacks remained.

.freeze/restore are used with hiberation where Linux restarts in a new
place in the future.  .suspend/resume are useful for runtime power
management for the duration of a boot.

The current behavior of the callbacks works for an xl save/restore or
live migration where the domain is restored/migrated to a new location
and connecting to a not-already-connected backend.

Change xenbus_pm_ops to use .freeze/thaw/restore and drop the
.suspend/resume hook.  This matches the use in drivers/xen/manage.c for
save/restore and live migration.  With .suspend/resume empty, PV devices
are left connected during s2idle and s3, so PV devices are not changed
and work after resume.

Signed-off-by: Jason Andryuk <jason.andryuk@amd.com>
Acked-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Message-ID: <20251119224731.61497-2-jason.andryuk@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: jandryuk

drivers/xen/xenbus/xenbus_probe_frontend.c

@@ -148,11 +148,9 @@ static void xenbus_frontend_dev_shutdown(struct device *_dev)
 }
 
 static const struct dev_pm_ops xenbus_pm_ops = {
-	.suspend	= xenbus_dev_suspend,
-	.resume		= xenbus_frontend_dev_resume,
 	.freeze		= xenbus_dev_suspend,
 	.thaw		= xenbus_dev_cancel,
-	.restore	= xenbus_dev_resume,
+	.restore	= xenbus_frontend_dev_resume,
 };
 
 static struct xen_bus_type xenbus_frontend = {