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 cc8fb474d5204ed3c2cf2c48bd754b1fdf3758c9..b92c4b077077371e2f420eb0d1e381fe95e2c852 100644 (file)
--- a/arch/powerpc/kernel/head_64.S
+++ b/arch/powerpc/kernel/head_64.S
@@ -1479,9 +1479,6 @@ __secondary_start:
        /* Load TOC */
        ld      r2,PACATOC(r13)
 
-       /* 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#]         */
@@ -1489,6 +1486,9 @@ __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