powerpc/book3s: Introduce exclusive emergency stack for machine check exception.

This patch introduces exclusive emergency stack for machine check exception.
We use emergency stack to handle machine check exception so that we can save
MCE information (srr1, srr0, dar and dsisr) before turning on ME bit and be
ready for re-entrancy. This helps us to prevent clobbering of MCE information
in case of nested machine checks.

The reason for using emergency stack over normal kernel stack is that the
machine check might occur in the middle of setting up a stack frame which may
result into improper use of kernel stack.

Signed-off-by: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
Acked-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 4 insertions, 0 deletions

diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
index af9d3469fb99..a90731b3d44a 100644
--- a/arch/powerpc/xmon/xmon.c
+++ b/arch/powerpc/xmon/xmon.c
@@ -2051,6 +2051,10 @@ static void dump_one_paca(int cpu)
         DUMP(p, stab_addr, "lx");
 #endif
         DUMP(p, emergency_sp, "p");
+#ifdef CONFIG_PPC_BOOK3S_64
+        DUMP(p, mc_emergency_sp, "p");
+        DUMP(p, in_mce, "x");
+#endif
         DUMP(p, data_offset, "lx");
         DUMP(p, hw_cpu_id, "x");
         DUMP(p, cpu_start, "x");