[PATCH AUTOSEL 5.7 254/388] xen/cpuhotplug: Fix initial CPU offlining for PV(H) guests

[Sasha Levin <sashal@xxxxxxxxxx>]

From: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>

[ Upstream commit c54b071c192dfe8061336f650ceaf358e6386e0b ]

Commit a926f81d2f6c ("xen/cpuhotplug: Replace cpu_up/down() with
device_online/offline()") replaced cpu_down() with device_offline()
call which requires that the CPU has been registered before. This
registration, however, happens later from topology_init() which
is called as subsys_initcall(). setup_vcpu_hotplug_event(), on the
other hand, is invoked earlier, during arch_initcall().

As result, booting a PV(H) guest with vcpus < maxvcpus causes a crash.

Move setup_vcpu_hotplug_event() (and therefore setup_cpu_watcher()) to
late_initcall(). In addition, instead of performing all offlining steps
in setup_cpu_watcher() simply call disable_hotplug_cpu().

Fixes: a926f81d2f6c (xen/cpuhotplug: Replace cpu_up/down() with 
device_online/offline()"
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Link: 
https://lore.kernel.org/r/1588976923-3667-1-git-send-email-boris.ostrovsky@xxxxxxxxxx
Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/xen/cpu_hotplug.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/drivers/xen/cpu_hotplug.c b/drivers/xen/cpu_hotplug.c
index ec975decb5de..b96b11e2b571 100644
--- a/drivers/xen/cpu_hotplug.c
+++ b/drivers/xen/cpu_hotplug.c
@@ -93,10 +93,8 @@ static int setup_cpu_watcher(struct notifier_block *notifier,
        (void)register_xenbus_watch(&cpu_watch);
 
        for_each_possible_cpu(cpu) {
-               if (vcpu_online(cpu) == 0) {
-                       device_offline(get_cpu_device(cpu));
-                       set_cpu_present(cpu, false);
-               }
+               if (vcpu_online(cpu) == 0)
+                       disable_hotplug_cpu(cpu);
        }
 
        return NOTIFY_DONE;
@@ -119,5 +117,5 @@ static int __init setup_vcpu_hotplug_event(void)
        return 0;
 }
 
-arch_initcall(setup_vcpu_hotplug_event);
+late_initcall(setup_vcpu_hotplug_event);
 
-- 
2.25.1