[PATCH v2] Fix the message in facility unavailable exception

[Balbir Singh <bsingharora@gmail.com>]

I ran into this during some testing on qemu. The current
facility_strings[] are correct when the trap address is
0xf80 (hypervisor facility unavailable). When the trap
address is 0xf60, IC (Interruption Cause) a.k.a status
in the code is undefined for values 0 and 1. This patch
adds a check to prevent printing the wrong information
and helps better direct debugging effort.

Signed-off-by: Balbir Singh <bsingharora@gmail.com>
---
 Changelog v2:
   Redo conditional checks as suggested by Michael

 arch/powerpc/kernel/traps.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index 023a462..010b11d 100644
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -1519,9 +1519,13 @@ void facility_unavailable_exception(struct pt_regs *regs)
 		return;
 	}
 
-	if ((status < ARRAY_SIZE(facility_strings)) &&
-	    facility_strings[status])
-		facility = facility_strings[status];
+	if ((hv || status >= 2) &&
+		(status < ARRAY_SIZE(facility_strings)) &&
+		facility_strings[status])
+			facility = facility_strings[status];
+	else
+		pr_warn_ratelimited("Unexpected facility unavailable exception "
+			"interruption cause %d\n", status);
 
 	/* We restore the interrupt state now */
 	if (!arch_irq_disabled_regs(regs))
-- 
2.5.5