[PATCH] powerpc/kernel: Avoid memory corruption at early stage

[Gavin Shan <gwshan@linux.vnet.ibm.com>]

When calling to early_setup(), we picks "boot_paca" up for the
master CPU and initialize that with initialise_paca(). At the
point, SLB shadow buffer isn't populated yet. Updating the SLB
shadow buffer should corrupt what we had in physical address 0
where the trap instruction is usually stored.

Signed-off-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
---
 arch/powerpc/kernel/paca.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/powerpc/kernel/paca.c b/arch/powerpc/kernel/paca.c
index d6e195e..048a6ee 100644
--- a/arch/powerpc/kernel/paca.c
+++ b/arch/powerpc/kernel/paca.c
@@ -115,6 +115,9 @@ static struct slb_shadow * __init init_slb_shadow(int cpu)
 {
 	struct slb_shadow *s = &slb_shadow[cpu];
 
+	if (!slb_shadow)
+		return NULL;
+
 	s->persistent = cpu_to_be32(SLB_NUM_BOLTED);
 	s->buffer_length = cpu_to_be32(sizeof(*s));
 
-- 
1.8.3.2