1 files changed, 44 insertions, 0 deletions

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 6c304438b503..2d643255c40d 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1698,6 +1698,50 @@ config HOTPLUG_CPU
             automatically on SMP systems. )
           Say N if you want to disable CPU hotplug.
 
+config BOOTPARAM_HOTPLUG_CPU0
+        bool "Set default setting of cpu0_hotpluggable"
+        default n
+        depends on HOTPLUG_CPU && EXPERIMENTAL
+        ---help---
+          Set whether default state of cpu0_hotpluggable is on or off.
+
+          Say Y here to enable CPU0 hotplug by default. If this switch
+          is turned on, there is no need to give cpu0_hotplug kernel
+          parameter and the CPU0 hotplug feature is enabled by default.
+
+          Please note: there are two known CPU0 dependencies if you want
+          to enable the CPU0 hotplug feature either by this switch or by
+          cpu0_hotplug kernel parameter.
+
+          First, resume from hibernate or suspend always starts from CPU0.
+          So hibernate and suspend are prevented if CPU0 is offline.
+
+          Second dependency is PIC interrupts always go to CPU0. CPU0 can not
+          offline if any interrupt can not migrate out of CPU0. There may
+          be other CPU0 dependencies.
+
+          Please make sure the dependencies are under your control before
+          you enable this feature.
+
+          Say N if you don't want to enable CPU0 hotplug feature by default.
+          You still can enable the CPU0 hotplug feature at boot by kernel
+          parameter cpu0_hotplug.
+
+config DEBUG_HOTPLUG_CPU0
+        def_bool n
+        prompt "Debug CPU0 hotplug"
+        depends on HOTPLUG_CPU && EXPERIMENTAL
+        ---help---
+          Enabling this option offlines CPU0 (if CPU0 can be offlined) as
+          soon as possible and boots up userspace with CPU0 offlined. User
+          can online CPU0 back after boot time.
+
+          To debug CPU0 hotplug, you need to enable CPU0 offline/online
+          feature by either turning on CONFIG_BOOTPARAM_HOTPLUG_CPU0 during
+          compilation or giving cpu0_hotplug kernel parameter at boot.
+
+          If unsure, say N.
+
 config COMPAT_VDSO
         def_bool y
         prompt "Compat VDSO support"