ARM: plat-versatile: move secondary CPU startup out of .init.

Hello,

I am implementing virtual CPU hotplug for the the ARM Cortex A-15 VExpress motherboard. This is mainly a QEMU feature, which allows dynamically changing the number of CPUs in the guest.

I stumbled upon a limitation in the kernel support for plat-versatile, which contains the secondary CPU startup code for the VExpress.

Basically, the secondary CPU startup code is preceded by the macro __INIT, which causes the code to be freed in free_initmem() during kernel_init().

This means that any attempt at hot-booting CPUs in the guest results in VCPUs jumping to a memory address that was freed, after which the VCPU behaves erratically, as can be expected.

With this patch applied, we use __CPUINIT instead of __INIT, so that the right thing happens:
under CONFIG_HOTPLUG_CPU, the secondary CPU startup code is not freed, the secondary VCPUs start successfully, and it's all gardens and blue skies.

Tested successfully using the ARM fast models for the Cortex-A15.

--
Claudio Fontana (1):
ARM: plat-versatile: move secondary CPU startup code out of .init.

 arch/arm/plat-versatile/headsmp.S | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

1.7.12.1

Using __CPUINIT instead of __INIT puts the secondary CPU startup code into the "right" section: it will not be freed in hotplug configurations, allowing hot-add of cpus, while still getting freed in non-hotplug configs.

index dd703ef..19fe180 100644
@@ -11,7 +11,7 @@
 #include <linux/linkage.h>
 #include <linux/init.h>
 
-	__INIT
+	__CPUINIT
 
 /*
  * Realview/Versatile Express specific entry point for secondary CPUs.

1.7.12.1

Using __CPUINIT instead of __INIT puts the secondary CPU startup code into the "right" section: it will not be freed in hotplug configurations, allowing hot-add of cpus, while still getting freed in non-hotplug configs.

index dd703ef..19fe180 100644
@@ -11,7 +11,7 @@
 #include <linux/linkage.h>
 #include <linux/init.h>
 
-	__INIT
+	__CPUINIT
 
 /*
  * Realview/Versatile Express specific entry point for secondary CPUs.

1.7.12.1

Using __CPUINIT instead of __INIT puts the secondary CPU startup code into the "right" section: it will not be freed in hotplug configurations, allowing hot-add of cpus, while still getting freed in non-hotplug configs.

Tested successfully on Fast-Models and on Arndale for VCPU hotplug.

index dd703ef..19fe180 100644
@@ -11,7 +11,7 @@
 #include <linux/linkage.h>
 #include <linux/init.h>
 
-	__INIT
+	__CPUINIT
 
 /*
  * Realview/Versatile Express specific entry point for secondary CPUs.

1.7.12.1

not quite sure how testing on Arndale verifies this change?

Otherwise looks ok to me (not guaranteeing that cpu hotplug will magically work for KVM using this change though).

-Christoffer