From c7dfb2591b23856182e2c9da6b1d526ef7fd6b2e Mon Sep 17 00:00:00 2001 From: "Longpeng(Mike)" Date: Wed, 9 Feb 2022 09:02:14 +0100 Subject: [PATCH] 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) Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Thomas Gleixner Tested-by: Dongli Zhang Reviewed-by: Valentin Schneider Reviewed-by: Henry Wang 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 f6bc0bc8a2aa..b9f54544e749 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. */ -- 2.34.1