powerpc: Initialise paca->kstack before early_setup_secondary

commit f761622e59433130bc33ad086ce219feee9eb961 upstream.

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>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S
index c38afdb45d7b066d2720d69a484f4c5a38ed71c0..a66c90b507e9175083c3d2d60eb0342c97ed23ff 100644 (file)
--- a/arch/powerpc/kernel/head_64.S
+++ b/arch/powerpc/kernel/head_64.S
@@ -563,9 +563,6 @@ __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#]         */
@@ -573,6 +570,9 @@ __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