powerpc: Reset kernel stack on cpu online from cede state

Cpu hotplug (offline) without dlpar operation will place cpu
in cede state and the extended_cede_processor() function will
return when resumed.

Kernel stack pointer needs to be reset before
start_secondary() is called to continue the online operation.

Added new function start_secondary_resume() to do the above
steps.

Signed-off-by: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
Cc: Gautham R Shenoy <ego@in.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S
index b24b700..bed9a29 100644 (file)
--- a/arch/powerpc/kernel/head_64.S
+++ b/arch/powerpc/kernel/head_64.S
@@ -617,6 +617,17 @@ _GLOBAL(start_secondary_prolog)
        std     r3,0(r1)                /* Zero the stack frame pointer */
        bl      .start_secondary
        b       .
+/*
+ * Reset stack pointer and call start_secondary
+ * to continue with online operation when woken up
+ * from cede in cpu offline.
+ */
+_GLOBAL(start_secondary_resume)
+       ld      r1,PACAKSAVE(r13)       /* Reload kernel stack pointer */
+       li      r3,0
+       std     r3,0(r1)                /* Zero the stack frame pointer */
+       bl      .start_secondary
+       b       .
 #endif
 
 /*

diff --git a/arch/powerpc/platforms/pseries/hotplug-cpu.c b/arch/powerpc/platforms/pseries/hotplug-cpu.c
index d1b124e..349e0af 100644 (file)
--- a/arch/powerpc/platforms/pseries/hotplug-cpu.c
+++ b/arch/powerpc/platforms/pseries/hotplug-cpu.c
@@ -146,12 +146,11 @@ static void pseries_mach_cpu_die(void)
                unregister_slb_shadow(hwcpu, __pa(get_slb_shadow()));
 
                /*
-                * NOTE: Calling start_secondary() here for now to
-                * start new context.
-                * However, need to do it cleanly by resetting the
-                * stack pointer.
+                * Call to start_secondary_resume() will not return.
+                * Kernel stack will be reset and start_secondary()
+                * will be called to continue the online operation.
                 */
-               start_secondary();
+               start_secondary_resume();
 
        } else if (get_preferred_offline_state(cpu) == CPU_STATE_OFFLINE) {
 

diff --git a/arch/powerpc/platforms/pseries/offline_states.h b/arch/powerpc/platforms/pseries/offline_states.h
index 202d869..75a6f48 100644 (file)
--- a/arch/powerpc/platforms/pseries/offline_states.h
+++ b/arch/powerpc/platforms/pseries/offline_states.h
@@ -35,4 +35,5 @@ static inline void set_default_offline_state(int cpu)
 
 extern enum cpu_state_vals get_preferred_offline_state(int cpu);
 extern int start_secondary(void);
+extern void start_secondary_resume(void);
 #endif