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cpu/hotplug: Allow the CPU in CPU_UP_PREPARE state to be brought up again.

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A CPU will not show up in virtualized environment which includes an
Enclave. The VM splits its resources into a primary VM and a Enclave
VM. While the Enclave is active, the hypervisor will ignore all requests to
bring up a CPU and this CPU will remain in CPU_UP_PREPARE state.

The kernel will wait up to ten seconds for CPU to show up (do_boot_cpu())
and then rollback the hotplug state back to CPUHP_OFFLINE leaving the CPU
state in CPU_UP_PREPARE. The CPU state is set back to CPUHP_TEARDOWN_CPU
during the CPU_POST_DEAD stage.

After the Enclave VM terminates, the primary VM can bring up the CPU
again.

Allow to bring up the CPU if it is in the CPU_UP_PREPARE state.

[bigeasy: Rewrite commit description.]

Signed-off-by: Longpeng(Mike) <longpeng2@huawei.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Dongli Zhang <dongli.zhang@oracle.com>
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Reviewed-by: Henry Wang <Henry.Wang@arm.com>
Link: https://lore.kernel.org/r/20220209080214.1439408-3-bigeasy@linutronix.de
This commit is contained in:
Longpeng(Mike) 2022-02-09 09:02:14 +01:00 committed by Thomas Gleixner
parent e8a69f12f0
commit c7dfb2591b
1 changed files with 7 additions and 0 deletions
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7
kernel/smpboot.c
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@ -392,6 +392,13 @@ int cpu_check_up_prepare(int cpu)
*/
return -EAGAIN;
case CPU_UP_PREPARE:
/*
* Timeout while waiting for the CPU to show up. Allow to try
* again later.
*/
return 0;
default:
/* Should not happen. Famous last words. */