powerpc: Initialise paca->kstack before early_setup_secondary

As early setup calls down to slb_initialize(), we must have kstack
initialised before checking "should we add a bolted SLB entry for our kstack?"

Failing to do so means stack access requires an SLB miss exception to refill
an entry dynamically, if the stack isn't accessible via SLB(0) (kernel text
& static data).  It's not always allowable to take such a miss, and
intermittent crashes will result.

Primary CPUs don't have this issue; an SLB entry is not bolted for their
stack anyway (as that lives within SLB(0)).  This patch therefore only
affects the init of secondaries.

Signed-off-by: Matt Evans <matt@ozlabs.org>
Cc: stable <stable@kernel.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 3 insertions, 3 deletions

diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S
index 844a44b64472..4d6681dce816 100644
--- a/arch/powerpc/kernel/head_64.S
+++ b/arch/powerpc/kernel/head_64.S
@@ -572,9 +572,6 @@ __secondary_start:
         /* Set thread priority to MEDIUM */
         HMT_MEDIUM
 
-        /* Do early setup for that CPU (stab, slb, hash table pointer) */
-        bl      .early_setup_secondary
-
         /* Initialize the kernel stack.  Just a repeat for iSeries.      */
         LOAD_REG_ADDR(r3, current_set)
         sldi    r28,r24,3               /* get current_set[cpu#]         */
@@ -582,6 +579,9 @@ __secondary_start:
         addi    r1,r1,THREAD_SIZE-STACK_FRAME_OVERHEAD
         std     r1,PACAKSAVE(r13)
 
+        /* Do early setup for that CPU (stab, slb, hash table pointer) */
+        bl      .early_setup_secondary
+
         /* Clear backchain so we get nice backtraces */
         li      r7,0
         mtlr    r7