The following commit has been merged into the smp/core branch of tip:
Commit-ID: c7dfb2591b23856182e2c9da6b1d526ef7fd6b2e
Gitweb: https://git.kernel.org/tip/c7dfb2591b23856182e2c9da6b1d526ef7fd6b2e
Author: Longpeng(Mike) <longpeng2@huawei.com>
AuthorDate: Wed, 09 Feb 2022 09:02:14 +01:00
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Tue, 12 Apr 2022 14:13:01 +02:00
cpu/hotplug: Allow the CPU in CPU_UP_PREPARE state to be brought up again.
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
---
kernel/smpboot.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/kernel/smpboot.c b/kernel/smpboot.c
index f6bc0bc..b9f5454 100644
--- a/kernel/smpboot.c
+++ b/kernel/smpboot.c
@@ -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. */