[POWERPC] Make emergency stack safe for current_thread_info() use

The current_thread_info() macro, used by preempt_count(), assumes the
base address and size of the stack are THREAD_SIZE aligned.

The emergency stack currently isn't either of these things, which
could potentially cause problems anytime we're running on the
emergency stack.  That includes when we detect a bad kernel stack
pointer, and also during early_setup_secondary().

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>

1 files changed, 6 insertions, 3 deletions

diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
index dff6308d1b5e..25e3fd8606ab 100644
--- a/arch/powerpc/kernel/setup_64.c
+++ b/arch/powerpc/kernel/setup_64.c
@@ -487,9 +487,12 @@ static void __init emergency_stack_init(void)
          */
         limit = min(0x10000000UL, lmb.rmo_size);
 
-        for_each_possible_cpu(i)
-                paca[i].emergency_sp =
-                __va(lmb_alloc_base(HW_PAGE_SIZE, 128, limit)) + HW_PAGE_SIZE;
+        for_each_possible_cpu(i) {
+                unsigned long sp;
+                sp  = lmb_alloc_base(THREAD_SIZE, THREAD_SIZE, limit);
+                sp += THREAD_SIZE;
+                paca[i].emergency_sp = __va(sp);
+        }
 }
 
 /*